KEY CONCEPTS
7.1 Cellular membranes are fluid mosaics of lipids and proteins
7.2 Membrane structure results in selective permeability
7.3 Passive transport is diffusion of a substance across a
membrane with no energy investment
7.4 Active transport uses energy to move solutes against their gradients
7.5 Bulk transport across the plasma membrane occurs by exocytosis and endocytosis
All living things are made of organized parts, obtain energy from their surroundings, perform chemical reactions, respond to their environment, grow and develop, change with time, and reproduce
All organisms are made of cells
All cells are produced from other cells (all cells arise from pre-existing cells by cell division)
The cell is the most basic unit of life
CELL CYCLE
CELL CYCLE CHECK POINT
PHASES IN CELL CYCLE CHECK POINT
ROLE OF CYLINE AND CDKS
MUTURATIONAL PROMOTING FACTOR
FUNCTION OF MPR
CONCLUSION
REFRENCE
All living things are made of organized parts, obtain energy from their surroundings, perform chemical reactions, respond to their environment, grow and develop, change with time, and reproduce
All organisms are made of cells
All cells are produced from other cells (all cells arise from pre-existing cells by cell division)
The cell is the most basic unit of life
CELL CYCLE
CELL CYCLE CHECK POINT
PHASES IN CELL CYCLE CHECK POINT
ROLE OF CYLINE AND CDKS
MUTURATIONAL PROMOTING FACTOR
FUNCTION OF MPR
CONCLUSION
REFRENCE
IT IS PPT ABOUT CELL MEMBRANE AFSHADFBHJADFKJDFBHJADFBHJDAFJHDFBVHCDBHJDJHDFSBHDFSJDFSHBJDFABHJDFSHJHDFSBJDFSBJDFSHJKDSFHJDFASKHFDSHJDFSKHKHKHFDSKHDFSKHDFSKHKDFHSKHDFSKHFSKHDFSKH
KEY CONCEPTS
43.1 In innate immunity, recognition and response rely on traits
common to groups of pathogens
43.2 In adaptive immunity, receptors provide pathogen-specific
recognition
43.3 Adaptive immunity defends against infection of body fluids and body cells
43.4 Disruptions in immune system function can elicit or exacerbate disease
KEY CONCEPTS
18.1 Bacteria often respond to environmental change by
regulating transcription
18.2 Eukaryotic gene expression is regulated at many stages
18.3 Noncoding RNAs play multiple roles in controlling gene
expression
18.4 A program of differential gene expression leads to the different cell types in a multicellular organism
18.5 Cancer results from genetic changes that affect cell cycle control
Chapter 16: Molecular Basis of InheritanceAngel Vega
KEY CONCEPTS
16.1 DNA is the genetic material
16.2 Many proteins work together in
DNA replication and repair
16.3 A chromosome consists of a DNA molecule packed together with proteins
Chapter 15: Chromosomal Basis of InheritanceAngel Vega
KEY CONCEPTS
15.1 Morgan showed that Mendelian inheritance has its physical
basis in the behavior of chromosomes: Scientific inquiry
15.2 Sex-linked genes exhibit unique patterns of inheritance
15.3 Linked genes tend to be inherited together because they are located near each other on the same chromosome
15.4 Alterations of chromosome number or structure cause
some genetic disorders
15.5 Some inheritance patterns are exceptions to standard
Mendelian inheritance
KEY CONCEPTS
14.1 Mendel used the scientific approach to identify two laws of inheritance
14.2 Probability laws govern Mendelian inheritance
14.3 Inheritance patterns are often more complex than predicted by simple Mendelian genetics
14.4 Many human traits follow Mendelian patterns of
inheritance
KEY CONCEPTS
13.1 Offspring acquire genes from parents by inheriting
chromosomes
13.2 Fertilization and meiosis alternate in sexual life cycles
13.3 Meiosis reduces the number of chromosome sets from diploid to haploid
13.4 Genetic variation produced in sexual life cycles contributes to evolution
KEY CONCEPTS
12.1 Most cell division results in genetically identical daughter cells
12.2 The mitotic phase alternates with interphase in the cell cycle
12.3 The eukaryotic cell cycle is regulated by a molecular
control system
KEY CONCEPTS
45.1 Hormones and other signaling molecules bind to target
receptors, triggering specific response pathways
45.2 Feedback regulation and coordination with the nervous system are common in endocrine signaling
45.3 Endocrine glands respond to diverse stimuli in regulating homeostasis, development,
and behavior
KEY CONCEPTS
11.1 External signals are converted to responses within the cell
11.2 Reception: A signaling molecule binds to a receptor protein, causing it to change shape
11.3 Transduction: Cascades of molecular interactions relay
signals from receptors to target molecules in the cell
11.4 Response: Cell signaling leads to regulation of transcription or cytoplasmic activities
11.5 Apoptosis integrates multiple cell-signaling pathways
KEY CONCEPTS
10.1 Photosynthesis converts light energy to the chemical energy of food
10.2 The light reactions convert solar energy to the chemical energy of ATP and NADPH
10.3 The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar
10.4 Alternative mechanisms of carbon fixation have evolved in hot, arid climates
Chapter 50: Sensory and Motor MechansimsAngel Vega
KEY CONCEPTS
50.1 Sensory receptors transduce stimulus energy and transmit signals to the central nervous system
50.2 The mechanoreceptors responsible for hearing and
equilibrium detect moving fluid or settling particles
50.3 The diverse visual receptors of animals depend on light-
absorbing pigments
50.4 The senses of taste and smell rely on similar sets of sensory receptors
50.5 The physical interaction of protein filaments is required for muscle function
50.6 Skeletal systems transform muscle contraction into
locomotion
KEY CONCEPTS
48.1 Neuron structure and organization reflect function in information transfer
48.2 Ion pumps and ion channels establish the resting potential of a neuron
48.3 Action potentials are the signals conducted by axons
48.4 Neurons communicate with other cells at synapses
KEY CONCEPTS
9.1 Catabolic pathways yield energy by oxidizing organic
fuels
9.2 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
9.3 After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules
9.4 During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
9.5 Fermentation and anaerobic respiration enable cells to
produce ATP without the use of oxygen
9.6 Glycolysis and the citric acid cycle connect to many other metabolic pathways
KEY CONCEPTS
8.1 An organism’s metabolism transforms matter and
energy, subject to the laws of thermodynamics
8.2 The free-energy change of a reaction tells us whether or not the reaction occurs
spontaneously
8.3 ATP powers cellular work by coupling exergonic reactions to endergonic reactions
8.4 Enzymes speed up metabolic reactions by lowering energy barriers
8.5 Regulation of enzyme activity helps control metabolism
KEY CONCEPTS
6.1 Biologists use microscopes and the tools of biochemistry to
study cells
6.2 Eukaryotic cells have internal membranes that
compartmentalize their functions
6.3 The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes
6.4 The endomembrane system regulates protein traffic and
performs metabolic functions in the cell
6.5 Mitochondria and chloroplasts change energy from one form to another
6.6 The cytoskeleton is a network of fibers that organizes structures and activities in the cell
6.7 Extracellular components and connections between cells help coordinate cellular activities
KEY CONCEPTS
5.1 Macromolecules are polymers, built from monomers
5.2 Carbohydrates serve as fuel and building material
5.3 Lipids are a diverse group of hydrophobic molecules
5.4 Proteins include a diversity of structures, resulting in a wide range of functions
5.5 Nucleic acids store, transmit, and help express hereditary
information
5.6 Genomics and proteomics have transformed biological inquiry and applications
KEY CONCEPTS
4.1 Organic chemistry is the study of carbon compounds
4.2 Carbon atoms can form diverse molecules by bonding to four other atoms
4.3 A few chemical groups are key to molecular function
Bio chapter 2: A Chemical Connection to BiologyAngel Vega
KEY CONCEPTS
2.1 Matter consists of chemical elements in pure form and
in combinations called compounds
2.2 An element’s properties depend on the structure of its atoms
2.3 The formation and function of molecules depend on chemical bonding between atoms
2.4 Chemical reactions make and break chemical bonds
Bio chapter 1 biochemistry, the cell, & geneticsAngel Vega
Evolution, the Themes of Biology, and Scientific Inquiry

KEY CONCEPTS
1.1 The study of life reveals common themes
1.2 The Core Theme: Evolution accounts for the unity and
diversity of life
1.3 In studying nature, scientists make observations and form and test hypotheses
1.4 Science benefits from a cooperative approach and
diverse viewpoints
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
1. Chapter 7
Membrane Structure and Function
In 1972, Singer and Nicolson proposed that the membrane is a
mosaic of proteins dispersed within a phospholipid bilayer, with only the
hydrophilic regions exposed to water. The fluid mosaic model states
that a membrane is a fluid structure with a “mosaic” of various proteins
embedded in it.
Function: The plasma
membrane exhibits selective
permeability, allowing some
substances to cross it more
easily than others
2. Cellular membranes are fluid
mosaics of lipids and proteins
• Membranes have two asymmetric leaflets
• Each leaflet has lateral fluidity
• Phospholipids are the most abundant lipid in the
plasma membrane (sphingolipids, glycolipids,
cholesterol also)—note: cholesterol only in animals &
some bacteria, not in plants
• Phospholipids are amphipathic molecules, containing
hydrophobic and hydrophilic regions
• The fluid mosaic model states that a membrane is a
fluid structure with a “mosaic” of various globular
proteins embedded in it—both integral and peripheral
4. Figure 7.3
Glyco-
protein Carbohydrate Glycolipid
EXTRACELLULAR
SIDE OF
MEMBRANE
Microfilaments
of cytoskeleton
Fibers of extra-
cellular matrix (ECM)
Cholesterol
Peripheral
proteins Integral
protein CYTOPLASMIC
SIDE OF
MEMBRANE
•Peripheral proteins usually on inner side of membrane & held their by ionic (with
charged lipid head) or hydrophobic (with a second hydrophobic protein) interaction
•Hydrophobic & hydrophilic regions of integral proteins
•Sugars usually on exterior leaflet; proteoglycans too
5. • Freeze-fracture studies of the plasma
membrane supported the fluid mosaic model
• Freeze-facture is a specialized preparation
technique that splits a membrane along the
middle of the phospholipid bilayer
7. Lateral movement
(~107
times per second)
Flip-flop
(~ once per month)
Movement of phospholipids
Rarely does a molecule flip-flop transversely across the membrane
8. LE 7-5b
ViscousFluid
Unsaturated hydrocarbon
tails with kinks
Saturated hydro-
carbon tails
•As temperatures cool, membranes switch from a fluid state to a
solid state
•The temperature at which a membrane solidifies depends on the
types of lipids
•Membranes rich in unsaturated fatty acids are more fluid than
those rich in saturated fatty acids
•Membranes must be fluid to work properly; they are usually
about as fluid as salad oil
9. Cholesterol
•The steroid cholesterol has different effects on
membrane fluidity at different temperatures
•At warm temperatures (such as 37°C), cholesterol
restrains movement of phospholipids
•At cool temperatures, it maintains fluidity by
preventing tight packing
11. • Six major functions of membrane proteins
– Transport
– Enzymatic activity
– Signal transduction
– Cell-cell recognition
– Intercellular joining
– Attachment to the cytoskeleton and
extracellular matrix (ECM)
12. Figure 7.7
(a) Transport (b) Enzymatic
activity
(c) Signal
transduction
(d) Cell-cell
recognition
(e) Intercellular
joining
(f) Attachment to
the cytoskeleton
and extracellular
matrix (ECM)
Enzymes
ATP
Signaling
molecule
Receptor
Signal transduction
Glyco-
protein
13. 1. Which of the following best describes the structure of a
biological membrane?
a. two layers of phospholipids with proteins embedded
between the two layers
b. a mixture of covalently linked phospholipids and proteins
that determines which solutes can cross the membrane
and which cannot
c. two layers of phospholipids with proteins either spanning
the layers or on the surface of the layers
d. a fluid structure in which phospholipids and proteins move
freely between sides of the membrane
e. two layers of phospholipids (with opposite orientations of
the phospholipids in each layer) with each layer covered
on the outside with proteins
14. 1. Which of the following best describes the structure of a
biological membrane?
a. two layers of phospholipids with proteins embedded
between the two layers
b. a mixture of covalently linked phospholipids and proteins
that determines which solutes can cross the membrane
and which cannot
c. two layers of phospholipids with proteins either spanning
the layers or on the surface of the layers
d. a fluid structure in which phospholipids and proteins move
freely between sides of the membrane
e. two layers of phospholipids (with opposite orientations of
the phospholipids in each layer) with each layer covered
on the outside with proteins
15. Sidedness of
Membranes
•Membranes have distinct
inside and outside faces
•The asymmetrical
distribution of proteins,
lipids and associated
carbohydrates in the
plasma membrane is
determined when the
membrane is built by the
ER and Golgi apparatus
Transmembrane
glycoproteins Secretory
protein
Golgi
apparatus
Vesicle
Attached
carbohydrate
ER
lumen
Glycolipid
Transmembrane
glycoprotein
Plasma membrane:
Cytoplasmic face
Extracellular face
Membrane
glycolipid
Secreted
protein
16. The Permeability of the Lipid
Bilayer
• Hydrophobic (nonpolar) molecules, such as
hydrocarbons, can dissolve in the lipid bilayer
and pass through the membrane rapidly
• Polar molecules, such as sugars, do not
cross the membrane easily
View Membrane Transport Video
17. Transport Proteins
• Transport proteins allow passage of hydrophilic
substances across the membrane
• Some transport proteins, called channel proteins, have
a hydrophilic channel that certain molecules or ions
can use as a tunnel
• Channel proteins called aquaporins facilitate the
passage of water
• Other transport proteins, called carrier proteins, bind
to molecules and change shape to shuttle them
across the membrane
• A transport protein is specific for the substance it
moves
18. Passive transport is diffusion of a
substance across a membrane with
no energy investment
• Diffusion is the tendency for molecules to
spread out evenly into the available space
• Although each molecule moves randomly,
diffusion of a population of molecules may
exhibit a net movement in one direction
• At dynamic equilibrium, as many molecules
cross one way as cross in the other direction
19. Figure 7.10
Molecules of dye Membrane (cross section)
WATER
(a) Diffusion of one solute
(b) Diffusion of two solutes
Net diffusion Net diffusion
Net diffusionNet diffusion
Net diffusion Net diffusion
Equilibrium
Equilibrium
Equilibrium
20. Effects of Osmosis on Water
Balance
• Osmosis is the diffusion of water across a
selectively permeable membrane
• The direction of osmosis is determined by a
difference in total solute concentration (but
pressure, gravity, matrix can influence)
• Water diffuses across a membrane from the
region of lower solute concentration (higher
water potential) to the region of higher solute
concentration (lower water potential)
21. Figure 7.11
Lower concentration
of solute (sugar)
Higher concentration
of solute
More similar
concentrations of solute
Sugar
molecule
H2O
Selectively
permeable
membrane
Osmosis
Selectively permeable
membrane: sugar
molecules cannot pass
through pores, but
water molecules can
22. Water Balance of Cells Without
Walls
• Tonicity is the ability of a solution to cause a
cell to gain or lose water
• Isotonic solution: solute concentration is the
same as that inside the cell; no net water
movement across the plasma membrane
• Hypertonic solution: solute concentration is
greater than that inside the cell; cell loses
water
• Hypotonic solution: solute concentration is less
than that inside the cell; cell gains water
24. Water Balance of Cells with
Walls
• Cell walls help maintain water balance
• A plant cell in a hypotonic solution swells until the
wall opposes uptake; the cell is now turgid (firm)
• If a plant cell and its surroundings are isotonic,
there is no net movement of water into the cell; the
cell becomes flaccid (limp), and the plant may wilt
• In a hypertonic environment, plant cells lose water;
eventually, the membrane pulls away from the
wall, a usually lethal effect called plasmolysis
Video: PlasmolysisVideo: Plasmolysis
25. LE 7-14
Filling vacuole
50 µm
50 µm
Contracting vacuole
The protist Paramecium, which is hypertonic to its pond water environment, has a
contractile vacuole that acts as a pump
26. 2. Which of the following statements about osmosis is
correct?
a. If a cell is placed in an isotonic solution, more water will
enter the cell than leaves the cell.
b. Osmotic movement of water into a cell would likely occur
if the cell accumulates water from its environment.
c. The presence of aquaporins (proteins that form water
channels in the membrane) should speed up the process
of osmosis.
d. If a solution outside the cell is hypertonic compared to the
cytoplasm, water will move into the cell by osmosis.
e. Osmosis is the diffusion of water from a region of lower water
concentration to a region of higher water concentration.
27. 2. Which of the following statements about osmosis is
correct?
a. If a cell is placed in an isotonic solution, more water will
enter the cell than leaves the cell.
b. Osmotic movement of water into a cell would likely occur
if the cell accumulates water from its environment.
c. The presence of aquaporins (proteins that form water
channels in the membrane) should speed up the process
of osmosis.
d. If a solution outside the cell is hypertonic compared to the
cytoplasm, water will move into the cell by osmosis.
e. Osmosis is the diffusion of water from a region of lower water
concentration to a region of higher water concentration.
28. Facilitated Diffusion: Passive
Transport Aided by Proteins
• In facilitated diffusion, transport proteins speed
movement of molecules across the plasma
membrane
• Channel proteins provide corridors that allow a
specific molecule or ion to cross the membrane
• Carrier proteins undergo a subtle change in
shape that translocates the solute-binding site
across the membrane
29. Figure 7.14
(a) A channel
protein
(b) A carrier protein
Carrier protein
Channel protein Solute
Solute
EXTRACELLULAR
FLUID
CYTOPLASM
30. Active transport uses energy to
move solutes against their gradients
• Facilitated diffusion is still passive because
the solute moves down its concentration
gradient
• Some transport proteins, however, can move
solutes against their concentration gradients
31. The Need for Energy in Active
Transport
• Active transport moves substances against
their concentration gradient
• Active transport requires energy, usually in the
form of ATP
• Active transport is performed by specific
proteins embedded in the membranes
• Active transport allows cells to maintain
concentration gradients that differ from their
surroundings
• The sodium-potassium pump is one type of
active transport system
32. Figure 7.15
EXTRACELLULAR
FLUID
CYTOPLASM
1 2
5
6
4
3
[Na+
] low
[K+
] high
[Na+
] high
[K+
] low
Na+
K+
K+
K+
K+
K+
K+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
ATP
ADP
P
P
P
i
P
Cytoplasmic Na+
bonds to
the sodium-potassium pump
Na+
binding stimulates
phosphorylation by ATP.
Phosphorylation causes
the protein to change its
conformation, expelling Na+
to the outside.
Extracellular K+
binds
to the protein, triggering
release of the phosphate
group.
Loss of the phosphate
restores the protein’s
original conformation.
K+
is released and Na+
sites are receptive again;
the cycle repeats.
34. Maintenance of Membrane
Potential by Ion Pumps
• Membrane potential is the voltage difference
across a membrane (differences in the
distribution of positive and negative ions across a
membrane)
• Two combined forces, collectively called the
electrochemical gradient, drive the diffusion of
ions across a membrane:
– A chemical force (the ion’s concentration
gradient)
– An electrical force (the effect of the membrane
potential on the ion’s movement)
36. Cotransport: Coupled Transport by
a Membrane Protein
• Cotransport occurs when active transport of a
solute indirectly drives transport of another
solute
• Plants commonly use the gradient of hydrogen
ions generated by proton pumps to drive active
transport of nutrients into the cell
38. 3. Which of the following amino acids would most
likely be present in the outer side (facing the lipid
tails) of a transmembrane domain of an integral
membrane protein?
a. a charged amino acid like lysine
b. a polar amino acid like serine
c. a special amino acid like glycine or
proline
d. a hydrophobic amino acid like valine
e. any of the above, with no preference
39. 3. Which of the following amino acids would most
likely be present in the outer side of a
transmembrane domain of an integral membrane
protein?
a. a charged amino acid like lysine
b. a polar amino acid like serine
c. a special amino acid like glycine or
proline
d. a hydrophobic amino acid like valine
e. any of the above, with no preference
40. 4. Assume that each of the following items experiences a
similar magnitude of energy difference driving their diffusion
across a pure lipid bilayer. If ranked in order from fastest to
slowest, which of the following items would likely be second in
terms of how much of it crosses the bilayer in a given time?
a. molecular oxygen
b. sucrose
c. insulin
d. glucose
e. water
41. 4. Assume that each of the following items experiences a
similar magnitude of energy difference driving their diffusion
across a pure lipid bilayer. If ranked in order from fastest to
slowest, which of the following items would likely be second in
terms of how much of it crosses the bilayer in a given time?
a. molecular oxygen (first because a gas)
b. Sucrose (needs active transport)
c. Insulin (ligand for receptor signaling)
d. Glucose (needs active transport)
e. Water (second from channels & size)
42. 5. Consider various transport systems in a hypothetical cell
(see figure). Which one of these systems would both be a
passive system and not alter the membrane potential through
its operation?
43. 5. Consider various transport systems in a hypothetical cell
(see figure). Which one of these systems would both be a
passive system and not alter the membrane potential through
its operation?
A
B
C
D
E
44. Bulk Transport: Exocytosis
• In exocytosis, transport vesicles migrate to the
membrane, fuse with it, and release their contents
• Many secretory cells use exocytosis to export their
products
Bulk Transport: Endocytosis
• In endocytosis, the cell takes in macromolecules by
forming vesicles from the plasma membrane
• Endocytosis is a reversal of exocytosis, involving
different proteins
• Small molecules and water enter or leave the cell through the
lipid bilayer or by transport proteins
• Large molecules, such as polysaccharides and proteins, cross
the membrane via vesicles (bulk transport)
46. LE 7-20c
Receptor
RECEPTOR-MEDIATED ENDOCYTOSIS
Ligand
Coated
pit
Coated
vesicle
Coat protein
Coat
protein
Plasma
membrane
0.25 µm
A coated pit
and a coated
vesicle formed
during
receptor-
mediated
endocytosis
(TEMs).
•Three types of endocytosis:
–Phagocytosis (“cellular
eating”): Cell engulfs
particle in a vacuole
–Pinocytosis (“cellular
drinking”): Cell creates
vesicle around fluid
–Receptor-mediated
endocytosis: Binding of
ligands to receptors
triggers vesicle formation
Editor's Notes
Figure 7.2 Phospholipid bilayer (cross section)
Figure 7.3 Updated model of an animal cell’s plasma membrane (cutaway view)
Figure 7.6 The structure of a transmembrane protein
Figure 7.7 Some functions of membrane proteins
Answer: C
Figure 7.10 The diffusion of solutes across a synthetic membrane
Figure 7.11 Osmosis
Figure 7.12 The water balance of living cells
Answer: C
Answer: C
Figure 7.14 Two types of transport proteins that carry out facilitated diffusion
Figure 7.15 The sodium-potassium pump: a specific case of active transport
Figure 7.16 Review: passive and active transport
Figure 7.18 Cotransport: active transport driven by a concentration gradient
Answer: D
Transmembrane domains primarily consist of helices of hydrophobic amino acids.
Answer: D
Transmembrane domains primarily consist of helices of hydrophobic amino acids.