The document summarizes the structure of plant and bacterial cell walls and plasma membranes. It describes the key components of plant cell walls, including cellulose microfibrils embedded in a matrix of other polysaccharides. It also discusses the differences between primary and secondary cell walls. For bacteria, it explains that gram-positive bacteria have a thick peptidoglycan layer while gram-negatives have a thinner peptidoglycan layer surrounded by an outer membrane containing lipopolysaccharides. The plasma membrane is introduced as a selectively permeable bilayer of lipids surrounding the cell.
This power point presentation consists of 64 slides including information about plant and other type of cell wall. Chemical composition, structure, function and properties of cell wall have been explained. Ultra structure of plant cell wall has also been high lighted. Algal,Fungal,Bacterial and Archaeal cell walls have also been explained.
• PRIMARY PIT FIELD
• PITS
• STRUCTURE OF PITS
• TYPES OF PITS
• COMBINATION IN PITS
• STRUCTURE OF BORDERED PITS
• COMBINATION IN BORDERED PITS
• PLASMODESMATA
• STRUCTURE OF PLASMODESMATA
• CLASSIFICATION OF PLASMODESMATA
• FUNCTION OF PLASMODESMATA
This power point presentation consists of 64 slides including information about plant and other type of cell wall. Chemical composition, structure, function and properties of cell wall have been explained. Ultra structure of plant cell wall has also been high lighted. Algal,Fungal,Bacterial and Archaeal cell walls have also been explained.
• PRIMARY PIT FIELD
• PITS
• STRUCTURE OF PITS
• TYPES OF PITS
• COMBINATION IN PITS
• STRUCTURE OF BORDERED PITS
• COMBINATION IN BORDERED PITS
• PLASMODESMATA
• STRUCTURE OF PLASMODESMATA
• CLASSIFICATION OF PLASMODESMATA
• FUNCTION OF PLASMODESMATA
Vascular Cambium & Seasonal activity & its Role in Stem & RootFatima Ramay
Vascular Cambium & Seasonal activity & its Role in Stem & Root:
The vascular cambium (pl. cambia or cambiums) is a lateral meristem in the vascular tissue of plants.
The vascular cambium is a cylindrical layer of cambium that runs through the stem of a plant that undergoes secondary growth.
In Dicots:
The vascular cambium is in dicot stems and roots, located between the xylem and the phloem in the stem and root of a vascular plant, and is the source of both the secondary xylem growth (inwards, towards the pith) and the secondary phloem growth (outwards).
In Monocots:
Monocot stems, such as corn, palms and bamboos, do not have a vascular cambium and do not exhibit secondary growth by the production of concentric annual rings. They cannot increase in girth by adding lateral layers of cells as in conifers and woody dicots.
Cambium of some plants remains active for the entire period of their life, i.e., cambial cells divide and resulting cells mature to form xylem and phloem elements.
This type of seasonal activity usually found in the plants present in the tropical regions, and not all plants show cambial activity.
Percentage of ringless trees in the rain forests of;India : 75%Amazon : 43%Malaysia : 15%
In regions with definite seasonal climate; seasonal activity of cambium ceased with onset of unfavorable conditions; In Autumn, it enters the dormant state and lasts for the end of summer; In Spring, cambium again becomes active.
Duration of cambial activity is also affected by day-length, e.g., In Robinia pseudoacacia, cambium is dormant under short-day condition.
The cambium cells formed in circular in cross section from the beginning onwards.
The cambial ring is partially primary (fascicular cambium) and partially secondary (interfascicular cambium).
Periderm originates from the cortical cells (extra stelar in origin).
In Dicot stem, for mechanical support xylem is with comparatively smaller vessels, greater fibers and less parenchyma.
More amount of cork is produces for protection.
Lenticels on periderm are very prominent.
The cambial ring formed is wavy in the beginning and later becomes circular.
The cambium ring is completely secondary in origin.
Periderm originates from the pericycle (intra stelar in origin).
In Dicot root, xylem is with big thin walled vessels with few fibers and more parenchyma.
Less amount of cork is produced as root is underground.
Lenticels on periderm are not very prominent.
Derived from the word latex meaning juice in latin. sometimes called lactiferous cells or vessels from the latin word for milk, lac
According to origin simple laticifer derived from a single cell or union of cells.
Laticifers can be defined as a specialized cell or a row of such cells that secrete the milky fluid termed latex. The word laticifer is used as a general term to denote the various latex-secreting structures latex cell, latex vessel, latex duct, latex tube and laticiferous duct. The laticiferous duct is a cavity into which latex is secreted.
The "Telome theory" of Walter Zimmermann (1930, 1952) is the most accepted theory that is based on fossil record and synthesizes the major steps in the evolution of vascular plants.
It describes how the primitive type of vascular plants developed from Rhynia like plants.
The slides has been edited. visit for new one on https://www.slideshare.net/alihaider408/stelar-system-stele-its-types-and-evolutionedited-182037813
Sorry for inconvenience.
Stele is defined as a central vascular cylinder, with or without pith and delimited the cortex by endodermis.
Van Tieghem and Douliot (1886) recognized only three types of steles.
1-Protostele
2-Siphonostele
3-Solenostele
Stelar Theory:
Major highlights of stellar theory are:
Stele is a real entity and present universally in all higher plants.
Cortex and stele are two fundamental parts of a shoot system
Stele and cortex are separated by endodermis
Vascular Cambium & Seasonal activity & its Role in Stem & RootFatima Ramay
Vascular Cambium & Seasonal activity & its Role in Stem & Root:
The vascular cambium (pl. cambia or cambiums) is a lateral meristem in the vascular tissue of plants.
The vascular cambium is a cylindrical layer of cambium that runs through the stem of a plant that undergoes secondary growth.
In Dicots:
The vascular cambium is in dicot stems and roots, located between the xylem and the phloem in the stem and root of a vascular plant, and is the source of both the secondary xylem growth (inwards, towards the pith) and the secondary phloem growth (outwards).
In Monocots:
Monocot stems, such as corn, palms and bamboos, do not have a vascular cambium and do not exhibit secondary growth by the production of concentric annual rings. They cannot increase in girth by adding lateral layers of cells as in conifers and woody dicots.
Cambium of some plants remains active for the entire period of their life, i.e., cambial cells divide and resulting cells mature to form xylem and phloem elements.
This type of seasonal activity usually found in the plants present in the tropical regions, and not all plants show cambial activity.
Percentage of ringless trees in the rain forests of;India : 75%Amazon : 43%Malaysia : 15%
In regions with definite seasonal climate; seasonal activity of cambium ceased with onset of unfavorable conditions; In Autumn, it enters the dormant state and lasts for the end of summer; In Spring, cambium again becomes active.
Duration of cambial activity is also affected by day-length, e.g., In Robinia pseudoacacia, cambium is dormant under short-day condition.
The cambium cells formed in circular in cross section from the beginning onwards.
The cambial ring is partially primary (fascicular cambium) and partially secondary (interfascicular cambium).
Periderm originates from the cortical cells (extra stelar in origin).
In Dicot stem, for mechanical support xylem is with comparatively smaller vessels, greater fibers and less parenchyma.
More amount of cork is produces for protection.
Lenticels on periderm are very prominent.
The cambial ring formed is wavy in the beginning and later becomes circular.
The cambium ring is completely secondary in origin.
Periderm originates from the pericycle (intra stelar in origin).
In Dicot root, xylem is with big thin walled vessels with few fibers and more parenchyma.
Less amount of cork is produced as root is underground.
Lenticels on periderm are not very prominent.
Derived from the word latex meaning juice in latin. sometimes called lactiferous cells or vessels from the latin word for milk, lac
According to origin simple laticifer derived from a single cell or union of cells.
Laticifers can be defined as a specialized cell or a row of such cells that secrete the milky fluid termed latex. The word laticifer is used as a general term to denote the various latex-secreting structures latex cell, latex vessel, latex duct, latex tube and laticiferous duct. The laticiferous duct is a cavity into which latex is secreted.
The "Telome theory" of Walter Zimmermann (1930, 1952) is the most accepted theory that is based on fossil record and synthesizes the major steps in the evolution of vascular plants.
It describes how the primitive type of vascular plants developed from Rhynia like plants.
The slides has been edited. visit for new one on https://www.slideshare.net/alihaider408/stelar-system-stele-its-types-and-evolutionedited-182037813
Sorry for inconvenience.
Stele is defined as a central vascular cylinder, with or without pith and delimited the cortex by endodermis.
Van Tieghem and Douliot (1886) recognized only three types of steles.
1-Protostele
2-Siphonostele
3-Solenostele
Stelar Theory:
Major highlights of stellar theory are:
Stele is a real entity and present universally in all higher plants.
Cortex and stele are two fundamental parts of a shoot system
Stele and cortex are separated by endodermis
Plant systems: Extracellular matrix components of plants-cell wall, cellulose and hemicelluloses, extensins, WAKs, secondary wall structure, pits-primary and secondary pits and their development, plasmodesmota-structure and functions, pectins, cutins, lignins, turnover of cell wall components
Bacteria- Bacteria, the oldest and most diversified creatures on our planet, have a structure that is both basic and interesting.
Key points-
cell envelope- Investigate the bacterial cell's outermost layers, including the cell wall, cell membrane, and any other components that defend and preserve cell integrity.
cytoplasm and nucleotide- Discover the inner workings of bacterial cells, where genetic material is stored, metabolism occurs, and critical functions are organised.
Appandages and Flagella-Learn about the many appendages that bacteria can have, such as flagella, pili, and fimbriae, and how they help in motility and adherence.
Inclusions and Granules:Learn how bacteria adapt to their surroundings by storing energy and critical chemicals in the form of inclusions and granules.
Structural variation-Explore the variety of bacterial structure across various species and how these changes contribute to their adaptation and success.
Interactions and Ecological Importance: Investigate how bacteria's structure effects their interactions with other species and their significance in ecosystems.
This slide is presented by
Deepti Negi
Assistant professor
Pharmacology
Shri Guru Ram Rai University
Dehradun
The cell wall that surrounded bacteria and many types of eukaryotic cell (fungi, algae an higher plant) determine cell shapes and prevent cell from and bursting as a osmotic pressure.
The cell wall of bacteria and eukaryotes are structurally very different because Bacteria cell wall consist polysaccharides cross linked by short peptide.
Cell wall consist of polysaccharides embedded in gel like matrix
Introduction
History
Structure of ribosome’s
Types of ribosome’s
Function of ribosome's
Conclusion
References
Introduction
What is extracellular matrix
What do extracellular matrix
Types of extracellular matrix
Extracellular matrix of plants
Extracellular matrix of animals
Connective tissues
Epithelial tissues
Function of collagen
Conclusions
References
Cell Biology and genetics paper - Mutation a basic touch to b.sc students with examples. DNA, genome, gene level mutation and chromosome level with examples. Touched some of the mutation types.
Dept. of Biotechnology, University College of Science, Tumkur Tumkur University, Tumakuru, Dr. Krishna presented department profile to NAAC peer team on 28/11/2018
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
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.
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.
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.
1. Ultra Structure of Cell Wall and
Plasma Membrane
By
DR. KRISHNA
Assistant Professor in Biotechnology
Tumkur University, Tumakuru
2. Introduction:
• The cell wall - rigid, semi-permeable protective layer in some cell types.
• Cell wall is positioned next to the cell membrane (plasma membrane) in
most plant cells, fungi, bacteria, algae, and some archaea.
• Animal cells however, do not have a cell wall.
• The cell wall conducts many important functions in a cell:
1. Protection, 2. Structure, 3. Support.
• Cell wall composition varies depending on the organism.
In plants - mainly of strong fibers of the carbohydrate polymer
cellulose.
Cellulose is the major component of cotton fiber and wood and is
used in paper production.
4. • There are at least 8000 to 15,000 glucose
monomers per cellulose molecule and are
0.25 to 0.5 µm long.
• The molecules are flat and ribbon like,
and lie parallel to each other. Hydrogen
bonding occurs between the molecules,
thus crystallizing and producing
aggregates. These aggregates are called
microfibril.
• Each microfibril contains 40 to 70 chains,
which lie side by side, and these can be
seen in Electron micrographs.
• The spaces between the microfibrils are
filled up with lignin, cutin, pectic
substances, hemicellulose, water etc.
Thus, the microfibril gains considerable
strength.
5. • In primary cell wall, the orientation of microfibril is transverse to
the long axis, and during growth the arrangement may be
longitudinal.
• The orientation in secondary wall may differ from primary wall.
Tracheids and fibres show three layers in their secondary wall the
outer layer (S1), the central layer (S2) and the inner layer (S3), among
which the central (S2) is the thickest.
• The S1 and S3 layers lie adjacent to primary wall and cell lumen
respectively.
• These layers S1, S2 and S3 may be distinguished by their respective
orientation of cellulose microfibrils.
• In S1 and S3, the microfibrils are in the form of a lax helix and in S2, it
is a steep one
6. Primary (growing) plant cell wall:
• Major carbohydrates are cellulose,
hemicellulose and pectin.
• cellulose microfibrils are linked via
hemicellulosic tethers to form the cellulose-
hemicellulose network, which is embedded
in the pectin matrix.
• Common hemicellulose in the primary cell
wall is xyloglucan
• Outer part of the primary cell wall of the
plant epidermis is usually impregnated with
cutin and wax
Secondary cell walls –range of compounds that modify their mechanical properties and permeability. The major polymers
that make up wood (largely secondary cell walls) include:
•cellulose, 35-50%
•xylan, 20-35%, a type of hemicellulose
•lignin, 10-25%, a complex phenolic polymer that penetrates the spaces in the cell wall between cellulose, hemicellulose
and pectin components, driving out water and strengthening the wall.
7. Layers of Cell wall
•The primary cell wall, generally a thin,
flexible and extensible layer formed while
the cell is growing.
•The secondary cell wall, a thick layer
formed inside the primary cell wall after
the cell is fully grown. It is not found in all
cell types. Some cells, such as the
conducting cells in xylem, possess a
secondary wall containing lignin, which
strengthens and waterproofs the wall.
•The middle lamella, a layer rich in
pectins. This outermost layer forms the
interface between adjacent plant cells and
glues them together.
8. Plant Cell Wall Function
A major role of the cell wall is to form a framework for the cell to prevent over
expansion. Cellulose fibers, structural proteins, and other polysaccharides help to
maintain the shape and form of the cell. Additional functions of the cell wall include:
• Support - the cell wall provides mechanical strength and support. It also controls the
direction of cell growth.
• Withstand turgor pressure - turgor pressure is the force exerted against the cell wall
as the contents of the cell push the plasma membrane against the cell wall. This
pressure helps a plant to remain rigid and erect, but can also cause a cell to rupture.
• Regulate growth - sends signals for the cell to enter the cell cycle in order to divide
and grow.
• Regulate diffusion - the cell wall is porous allowing some substances, including
proteins, to pass into the cell while keeping other substances out.
• Communication - cells communicate with one another via plasmodesmata (pores or
channels between plant cell walls that allow molecules and communication signals
to pass between individual plant cells).
• Protection - provides a barrier to protect against plant viruses and other pathogens.
It also helps to prevent water loss.
• Storage - stores carbohydrates for use in plant growth, especially in seeds.
9. The Cell Wall of Bacteria
• cell wall in prokaryotic bacteria is composed of peptidoglycan.
• Peptidoglycan is a polymer composed of double-sugars and amino
acids (protein subunits).
• This molecule gives the cell wall rigidity and helps to give bacteria
shape.
• Peptidoglycan molecules form sheets which enclose and protect
the bacterial plasma membrane.
• The cell wall in gram-positive bacteria contains several layers of
peptidoglycan. These stacked layers increase the thickness of the
cell wall.
• In gram-negative bacteria, the cell wall is not as thick because it
contains a much lower percentage of peptidoglycan.
• The gram-negative bacterial cell wall also contains an outer layer
of lipopolysaccharides (LPS).
• The LPS layer surrounds the peptidoglycan layer and acts as an
endotoxin (poison) in pathogenic bacteria (disease causing
bacteria).
• The LPS layer also protects gram-negative bacteria against certain
antibiotics, such as penicillins.
12. Composition of cell wall:
1. Peptidoglycan:
• Peptidoglycan is porous cross linked polymer which is responsible for strength of
cell wall.
• Peptidoglycan is composed of three components.
• Glycan backbone
• Tetra-peptide side chain ( chain of 4 amino acids) linked to NAM
• Peptide cross linkage
• Glycan backbone is the repeated unit of N-acetyl muramic acid (NAM) and N-
acetyl glycosamine (NAG) linked by β-glycosidic bond.
• The glycan backbone are cross linked by tetra-peptide linkage. The tetra-peptide
are only found in NAM.
• More than 100 peptidoglycan are known with the diversity focused on the
chemistry of peptide cross linkage and interbridge.
• Although the peptidoglycan chemistry vary from organism to organism the glycan
backbone ie NAG-NAM is same in all species of bacteria.
13. The aminoacids found in tetra-peptide are-
•L-alanine: 1st position in both gm+ve and
gm-ve bacteria
•D-glutamic acid: 2nd position
•D-aminopimelic acid/ L-lysine: 3rd position
(variation occurs)
•D-alanine: 4th position
14. Peptide cross linkage in Gram positive and Gram negative bacteria:
•In gram negative bacteria, peptide cross
linkage occur between Diaminopamilic
acid (3rd position) of one glycan back
bone and D-alanine of adjacent glycan
back bone.
•In gram positive bacteria, peptide cross
linkage occur by peptide interbridge. The
type and number of aminoacids in
interbridge vary among bacterial
species.
15. 2. Teichoic acid:
• Teichoic acid is water soluble polymer of
glycerol or ribitol phosphate.
• It is present in gram positive bacteria.
• It constitutes about 50% of dry weight of
cell wall.
• It is the major surface antigen of gram
positive bacteria.
3. Outer membrane
• It is an additional layer present in gram
negative bacteria.
• It is composed of lipid bilayer, protein
and lipopolysaccharide (LPS) layer
Function of outer membrane:
• Structure component of gram-ve cell
wall
• LPS is an endotoxin produced by gram –
ve bacteria
• Lipid-A is antigenic Figure: Outer membrane in cell wall of gram negative bacteria
16. 4. LPS
• LPS is attached to outer membrane by hydrophobic bond. LPS is synthesized in cytoplasmic
membrane and transported to outer membrane.
• LPS is composed of lipid-A and polysaccharide.
• Lipid-A: it is phosphorylated glucosamine disaccharide.
• Polysaccharide: it consists of core-polysaccharide and O-polysaccharide.
Gram positive bacteria
• Micrococcus
• Staphylococcus
• Streptococcus
• Leuconostoc
• Gram negative bacteria
• E. coli
• Salmonella
• Klebsiella
• Shigella
• Pseudomonas
17. Cell Membrane:
•The term was originally used by Nageli and Cramer (1855) for
the membranous covering of the protoplast. The same was
named plasmalemma by Plowe (1931).
•Plasmalemma or plasma membrane was discovered by
Schwann (1838).
Membranes also occur inside the cytoplasm of eukaryotic cells as
covering of several cell organelles like nucleus, mitochondria,
plastids, lysosomes, golgi bodies, peroxisomes, etc.
18. Models and Ultrastructure of Plasma Membrane
The top four historical models of Plasma Membrane.
The models are: 1. Lipid and Lipid Bilayer Models 2. Unit Membrane Model (Protein-Lipid
Bilayer-Protein) 3. Fluid Mosaic Model 4. Dannelli Model.
1. Lipid and Lipid Bilayer Model:
• This model to explain the structure of plasma membrane was given by Overton, Gorion
and Grendel. Previously only indirect information was available to explain the structure
of plasma membrane. In 1902, Overton observed that substances soluble in lipid could
selectively pass through the membranes. On this basis he stated that plasma membrane
is composed of a thin layer of lipid.
• Subsequently, Gorter and Grendel in 1926 observed that the extracted from erythrocyte
membranes was twice the amount expected if a single layer was present throughout the
surface area of these cells. On this basis they stated that plasma membrane is made up
of double layer of lipid molecules. These models of Gorter and Grendel could not explain
the proper structure of plasma membrane but they put the foundation of future models
of membrane structure.
19. 2. Unit Membrane Model (Protein-Lipid Bilayer-Protein):
• This is also known as unit membrane model. This model was
proposed by Davson, Daniell and Robertson. When surface tension
measurements made on the membranes, it suggests the presence of
proteins. After the existence of proteins the initial lipid bilayer model
proposed by Gorter and Grendel was modified. It was suggested that
surface tension of cells is much lower than what one would expect if
only lipids were involved.
• It may also be observed that if protein is added to model lipid water
system, surface tension is lowered. This suggested indirectly the
presence of proteins. On this basis Davson and Danielli proposed that
plasma membrane contained a lipid bilayer with protein on both
surfaces.
20. • Initially they supposed that proteins existed as covalently bonded globular
structures bound to the polar ends of lipids. Subsequently they developed
the model in which the protein appears to be smeared over the hydrophilic
ends of the lipid bilayer. This model makes its popularity for a long time.
• With the availability of electron microscope later, fine structure of plasma
membrane could be studied. Definite plasma membrane of 6 nm to 10 nm
(10nm = 100 Å; 1 nm = 10_6mm) thickness was observed on surface of all
cells, and plasma membranes of two adjacent cells were found to be
separated by a space, 1-15nm wide.
• It was also observed that the plasma membrane of most of the cells
appeared to be three layered. Two outer dense layers were about 2.0nm
thick and the middle layer about 3.5nm. The early ideas of Gorter and
Grendel and those of Davson and Danielli were first formalized by
Robertson in 1959 in the form of his unit membrane concept.
21. • This concept of unit membrane with three layers (two protein layers
and one lipid bilayer) only supported the concept proposed earlier by
Davson and Danielli. In this unit membrane the less dense middle
layer corresponded to hydrocarbon chains of lipids. Thickness of
unit membrane (10nm) was found to be greater in plasma membrane
than in intracellular membranes of endoplasmic reticulum or golgi
complex.
22. 3. Fluid Mosaic Model:
• To explain the structure plasma membrane various models have been put
forward from time to time. But none was universally accepted. In this
relation Gorter and Grendel, Davson and Danielli, etc. proposed model for
plasma membrane after that Fluid Mosaic Model for plasma membrane
was proposed which was universally accepted.
• It was proposed by Singer and Nicholson (1912). This model postulates that
lipid and integrated proteins are disposed in a sort of mosaic pattern and
all the biological membranes have a quasi-fluid structure where both lipid
and protein components are able to perform transitional movement within
lipid bilayer.
• In this model, lipid molecules may exhibit intra-molecular movement or
may rotate about their axis or may display flip-flop movement including
transfer from one side of bilayer to the other. Thus this concept implies
that main components of the membrane, i.e., lipids, proteins and
oligosaccharides are held together by means of non-covalent interactions
as suggested by Gitler (1972). A term amphipathy was coined by Hartley
(1936) to the molecules having both hydrophilic and hydrophobic groups.
Thus lipids and integrated proteins are amphipatic in nature.
23. 4. Dannelli Model:
• (i) Lipid and intrinsic proteins are present in a mosaic arrangement
and
• (ii) Biological membranes are semifluid so that lipids as well as
intrinsic proteins are able to make movements within the bilayer.
This concept of fluidity implies that lipids, proteins and
oligosaccharides are held in their positions by means of non-covalent
interactions. On this basis, it can be stated that components can be
dispersed by solvents or detergents without breaking any bonds.
Intrinsic proteins are also intercalated to greater or lesser extent into a
continuous lipid bilayer. Such proteins may be in contact with an
aqueous solvent on both sides of the membrane.
24. Sandwich Model (Lamellar Models) of Plasma Membrane
• Denielli and Davson have proposed that in the plasma membrane a double layer
lipid molecule is sandwiched between the two different layers of protein
molecules. The lipid layers are found internally and the protein molecules are
found externally. The inner ends of lipid molecules are non-polar and
hydrophobic where as outer ends are polar and hydrophilic.
James Danielli and Hugh Davson in 1935
25. Unit Membrane Model of Plasma Membrane
• Robertson in the year 1953 proposed the unit membrane model
consisting of three layers of the plasma membrane and it is
complimentary to the sandwich model. According to this there are
two outer layers of protein molecules each with 20 angstroms thick,
embracing a central layer of lipid molecules of about 35 angstroms
thick for a total thickness of 75 angstroms.
Robertson Model:
J. David Robertson
(1959) modified the
model of Danielli and
Davson by proposing
that the lipid bilayer is
covered on the two
surfaces by extended or
(3-protein molecules)