3.0 Cell Structure and function (2).pptx

INTRODUCTION
Basic living unit structure and function of
the body.
 > 100 trillion cells in the body.
 Very small.
 Highly organized.
 Variety of sizes and shapes.
 Each type of cell has a special fxn.

Number of Cells
 Although ALL living things are made of
cells, organisms may be:
 Unicellular – composed of one cell.
 Multicellular- composed of many cells that
may organize into tissues, etc.

Variety of sizes and shapes
Cells in multicellular organisms often
specialize (take on different shapes &
functions)

Cell Specialization
 Cells in a multi-
cellular organism
become specialized
by turning different
genes on and off.
 This is known as
DIFFERENTIATION

Discovery of Cells
 1665- English Scientist, Robert Hooke, discovered
cells while looking at a thin slice of cork.
 He described the cells as tiny boxes or a
honeycomb.
 He thought that cells only existed in plants and
fungi

Development of Cell Theory
 1838- German Botanist, Matthias Schleiden,
concluded that all plant parts are made of
cells
 1839- German physiologist, Theodor
Schwann, who was a close friend of
Schleiden, stated that all animal tissues are
composed of cells.

Development of Cell Theory
 1858- Rudolf Virchow, German physician,
after extensive study of cellular pathology,
concluded that cells must arise from
preexisting cells.

The Cell Theory Complete
 The 3 Basic Components of the Cell Theory
were now complete:
 1. All organisms are composed of one or
more cells. (Schleiden & Schwann)(1838-39)
 2. The cell is the basic unit of life in all living
things. (Schleiden & Schwann)(1838-39)
 3. All cells are produced by the division of
preexisting cells. (Virchow)(1858)

Modern Cell Theory
Modern Cell Theory contains 4 statements, in
addition to the original Cell Theory:
 The cell contains hereditary information(DNA)
which is passed on from cell to cell during cell
division.
 All cells are basically the same in chemical
composition and metabolic activities.
 All basic chemical & physiological functions are
carried out inside the cells.(movement,
digestion,etc)
 Cell activity depends on the activities of sub-cellular
structures within the cell(organelles, nucleus,
plasma membrane)

All cells share certain characteristics:
 General cell structure and component.
 General mechanisms of changing nutrients
to energy.
 Deliver end products into their surrounding
fluid.
 Almost all have the ability to reproduce.

Types
Prokaryotic cell.
Eukaryotic cell.

PROKARYOTIC CELL
Prokaryotic cell structure:
Small (1-10 μm) with a plasma membrane surrounded
by a rigid cell wall - in many the cell wall is made of
peptidoglycan - carbohydrate cross-linked with
polypeptides.
Cell wall may be covered with a capsule made of
polysaccharides
Few or no membrane enclosed spaces within the
cytoplasm.
No true nucleus - DNA is in a region called the
Nucleoid.
DNA is circular and naked (has no protein
associated with it)

Membrane enclosed spaces allow cell
functions to be compartmentalized and
isolated from other functions.
Prokaryotes lack membrane enclosed spaces
in their cytoplasm.
Some prokaryotes are photosynthetic. The
biochemical machinery for trapping light
energy is contained within a highly folded
plasma membrane.

Cytoplasm
Watery soft gel: 80% Water {20% Salts-
Proteins)
Contains – organic & inorganic solutes
Vitamins, Co-enzymes, ribosomes etc

Cytoplasm
 Chromosome
DNA is circular, Haploid
◦ single, circular, double-stranded DNA
molecule that contains all the genetic
information required by a cell.
◦ DNA is aggregated in a dense area called
the nucleoid.

 Plasmids; extra circular DNA
◦ Antibiotic Resistance.
 No organelles (Mitochondria, Golgi, etc.)but
contains organic and inorganic solutes: vitamins,
coenzymes, etcs.
 Granules (stores reserve materials) such as lipids,
volutin and polysaccharide.

Cell membrane
 Phospholipid bilayer with embedded proteins –
fluid mosaic model.
 Water can penetrate
 Flexible
 Not strong, ruptures easily
 Osmotic Pressure created by cytoplasm

Fxns of the Cell membrane
 Selective permeability: active & passive
 Secretion of hydrolytic enzymes.
 Has enzymes and carrier molecules for the
synthesis of DNA and cell wall.

Cell Wall
Rigid, 10-25 nm thick.
Supports the weak cell membrane.
Gives the bacteria its shape.
Peptido-glycan Polymer (amino acids +
sugars)
- Unique to bacteria
Sugars; NAG & NAM
◦ N-acetylglucosamine
◦ N-acetymuramic acid

Eukaryotic cell structure
Larger (10 - 100 μm) with a typical plasma
membrane - some with a cell wall.
Many organelles and other interior spaces
enclosed by membranes:
Eg Nucleus, Endoplasmic reticulum, Golgi
apparatus, Mitochondria, Chloroplasts,
Lysosomes,Vacuoles, Vesicles
Cytoplasm with a cytoskeleton - protein tubules
and fibers.
Cell wall found in plants (cellulose), fungi (chitin),
some protists but absent in animal cells, WHY?

Why animal cells lack cell wall
 Animals have only cell membranes made up of
phospholipid bilayer and protein which protects and
hold together the cell and its parts,
 it does not need to provide the support that plant cell
was provide because animals have other forms of
support ( i.e. exoskeletons and endoskeletons)
 and the lack of the cell wall allows for increased
flexibility and advanced cell/tissue specialization,
which plants cannot achieve.

General Eukaryotic Cell Structure
Eukaryotic cells: Highly organized
Three principal parts:
 Plasma (cell) membrane
 Cytoplasm & Organelles
 Nucleus.

PLASMA MEMBRANE
Surrounds, hold cell together and gives it
form.
Not solid.
Separates cell’s internal structures from
extracellular envt.
Its selectively permeable, & controls passage
of materials into and out of cells.
Participates in intracellular communication.

Functions of Plasma membrane
 Regulates passage of materials.
 Participates in biochemical reactions.
 Receives information about environment.
 Communicates with other cells

Composition
Plasma cell membrane is composed of:
 Double layer of phospholipids (hydrophobic
and hydrophilic parts)
 Protein span, or partially span membrane.
 Negatively charged carbohydrates attached
to the outer surface.

BIOLOGICAL PROPERTIES OF PLASMA
MEMBRANE
 Flexibility- permits shape changes that
accompany cell growth and movement.
 Ability to break and reseal.
 Selectively permeable- retain certain
compounds and ions within cells or specific
cellular compartments, while excluding others.

General Composition of the cell membrane
Proteins ………………………..55%
Lipids ……………………………41%
 Phospholipids ..25%
 Cholesterol …….12%
 Glycolipids ……..4%
Carbohydrates ……………….3%

Cell Membrane Phospholipids
Consist of:
a. Glycerol head that contains phosphate
group (polar and hydrophilic head)
b. 2 fatty acid “tails’ (non polar and
hydrophobic)
The hydrophobic parts restricts the passage
of water and water -soluble ions.

Cell Membrane Proteins
1. Integral Proteins:
 Also called Internal or Intrinsic Proteins.
-span the membrane/penetrate lipid bilayer,
usually across whole membrane
eg; transport proteins.
transmembrane protein.
- provides structural channels.

2. Peripheral Proteins:
 Also called External or Extrinsic Proteins.
- embedded in one side of the membrane.
eg; carrier proteins.
- binds with subst. to be transported.
- loosely bound to surface of membrane
cell, surface identity marker (antigens).

Gen. fxns of Cell membrane
Proteins
Provides structural support.
Transports molecules across membrane.
Some fxn as receptors for hormones.
Some fxn as regulatory molecules, that arrive
at outer surface of the molecules.
Some act as antigens and induce the process
of antibody formation.

Cell membrane Carbohydrate
Primarily attached to the outer surface of
the membrane.
- Glycoproteins. (mostly)
- Glycolipids.
Fxns
1. Attach cells to each other.
2. Act as a receptor substance.

Cytoplasm and Organelle.
CYTOPLASM
The aqueous content of a cell(fluid, jellylike
sustance that lies bn the cell membrane and
nucleus in which organelles are embedded.
Serves as a medium in which chemical rxns
occur.
The fluid portion of the cytoplasm is called
CYTOSOL.

Cellular Organelles
Organelles are membrane bound subcellular
structures within the cytoplasm which
perform specific functions.

Nucleus
 The largest and most obvious
membrane bound compartment - controls
cell activities.
It contains the nucleolus - a darkened
region where ribosomal RNA is
synthesized.
It contains chromosomes - consist of
DNA wrapped around proteins.
Chromosomes are the carriers of genes

Fxns of the nucleus
 Serves as the repository of genetic information.
 Site for DNA replication, transcription and RNA
processing.

Nucleus organization
 Three major structures of the nucleus are:
 1. The nuclear envelope & the lamina
 2.The nuclear pore
 3.The nucleolus

Structures
 1.Nuclear envelope: separates nuclear and
cytoplasmic constituents, allows limited
exchange between nucleus and cytoplasm.
Through the nuclear pore.
 Consist of two nuclear membranes(outer
and inner), a lamina that is apposed to the
inner membrane and a nuclear pore

 The lumen of the ER connects directly to the
inter-membranous space
 the outer membrane is continuous with the
ER.
 Ribosomes are attached to the outer
membrane on the cytoplasmic side.

Each nuclear membrane is a phospholipid
bilayer.
The critical fxn of the nuclear membrane is
to separate the content of the nucleus with
the cytoplasm.

The lamina
 It consists of lamins which are intermediate
filament proteins of the cytoskeleton.
Fxns:
 The nuclear lamina provides the support
framework for the nucleus.
 It also provides site for chromatin
attachment.
 It maintains the even distribution of nuclear
pores over the envelope.

Nuclear pore complex
 It provides channels for the transport of
small molecules, ions and macromolecules
(proteins and RNA)
 Small molecules and proteins with small
mass (50kd) cross freely –nucleus to
cytoplasm and vice versa.
 Protein and RNA are however selectively
exported actively and only in one direction.

 3-D structures of the NPC reveals an eight
spoke symmetry organized around a large
central pore.
 The spokes are connected to rings at the
nuclear and cytoplasmic surfaces.
 These are held by filaments extending from
the cytoplasmic and nuclear rings to form a
basket like structure when view from the
nuclear side.

Selective transport of proteins to and
from the nucleus
Proteins transported from the cyto to
nucleus- histones, DNA polymerases,
RNA polymerases, transcription
factors, splicing factors etc.

Nucleolus
The nucleolus lacks a membrane.
Fxns:
 It is the ribosome factory of the cell.
 It functions as an anchoring site for
chromosomes.

Morphologically 4 regions are distinguishable within
the nucleolus -
1. fibrillar center(contains the DNA that is not being
transcribed),
2. dense fibrillar component (contains many RNAs
being transcribed),
3. granular component-representing sites for
progressive stages of transcription, RNA
processing and ribosome assembly)
4. and the nucleolar matrix that may participate in
the organization of the nucleolus.
 In cells actively synthesizing proteins the nucleolus
is large and vice versa.

Chromosome - “colored body”
consists of both DNA and protein - seen as
chromosomes when highly condensed in
preparation for cell division.
At other times the DNA and protein are
threadlike and called chromatin.
The most common proteins are histones.
DNA is coiled around histones in a regular
pattern that produces structures called
nucleosomes.

Endoplasmic reticulum (ER)
 It is a network of membrane enclosed tubules
and sacs (cisternae) extending from the
nuclear membrane.
 Has ramifications throughout the cytoplasm.
 Serves as entry point for protein destined for
the ER and other organelles.
 It is also the site for protein folding, assembly
of multisubunit proteins, disulfide bond
formation, glycosylation and addition of
glycolipids to some plasma membrane
proteins.

Types of ER
1.rough ER - studded with ribosomes site of
synthesis of many proteins.
All ribosomes on rER are actively involved in
protein synthesis.
2. smooth ER - site for synthesis of
steroids and other lipids, Ca++ storage in muscles,
detoxification of drugs, toxins, alcohol (especially
in liver)
The highly convoluted surface provides a large
surface area for enzymatic activities. Many
enzymes are imbedded in the membranes.

Functions:
Circulation and transport.
Storage of proteins and minerals.
Synthesis of lipids, carbohydrates, and
proteins.
A large surface area for enzyme action.

ER
 Two kinds of proteins are transferred from the
cytosol to the ER.
A. Water soluble proteins are completely
translocated across the ER membrane and into the
lumen.
 They are destined for either secretion(by release at
the cell surface) or for the lumen of an organelle.
B. Transmembrane proteins are only partially
translocated across the ER and become embedded
in it
 They are destined to reside in the ER, the
membrane of another organelle or the plasma
membrane

Ribosomes
 Protein synthetic machinery.
 Two subunits - large and small
 Each made of protein and ribosomal RNA
(rRNA).
Subunits associate when they are
synthesizing proteins.
 protein synthesis occurs on ribosomes that
are free-floating in the cytoplasm and on
ribosomes attached to ER.
 rRNA is synthesized in the nucleolus.

Each ribosome is divided into two
subunits.
The smaller subunit binds to the
mRNA pattern, while the larger subunit
binds to the tRNA and the amino acids.
 When a ribosome finishes reading an
mRNA molecule, these two subunits
split apart.

Golgi Apparatus
A collection of membranes associated with
the ER.
composed of flatten sacs called cisternae.
concentrates and packages proteins
synthesized on the ER.
The Golgi is functionally associated with the
ER.

Proteins synthesized on the ER are
concentrated internally and transport
vesicles are budded off.
Transport vesicles fuse with the Golgi,
dump their contents into the Golgi.
Golgi packages proteins in vesicles so that
they may be excreted from the cell, or used
within the cell.

Secretory vesicles - used for excretion.
Leave the Golgi and move to plasma
membrane where they fuse and dump their
contents outside.
This is seen in many glands.
Secretory pathway
rER-->Golgi- ->Secretory Vesicle-->Cell
exterior

The Golgi Apparatus also forms lysosomes.
Lysosomes are vesicles filled with digestive
enzymes - used for intracellular digestion.
Particles can be taken into cell by
phagocytosis and vesicle fused with
lysosome.
The components of organelles can be
recycled after digestion by lysosomes

LYSOSOMES
 Potentially dangerous hydrolytic enzymes
functioning in acidic conditions (pH 5) are
segregated in the lysosomes to protect the other
components of the cell from random destruction.
 Lysosomes are bound by a single phospholipid
bilayer membrane.
 They vary in size and are formed by the fusion of
Golgi-derived vesicles with endosomes derived
from the cell surface.

 Enzymes known to be present in the lysosomes
include hydrolases that degrade proteins, nucleic
acids, lipids, glycolipids, and glycoproteins.
 Hydrolases are most active in the acidity maintained
in the lysosomes.
 After the material is broken down, lipids and amino
acids are transported across the lysosomal
membrane by permeases for use in biosynthesis.
 The remaining debris generally stays within the
lysosome and is called a residual body.

Mitochondria
Cellular powerhouses - the site of much
of the energy harvest by cells.
They have double membrane structure.
 Inner and Outer membranes.
Inner membrane folded into inward
projections called cristae.
Two spaces within the mitochondrion -
the matrix and the intermembrane
space.

The site of oxygen consumption within cells.
Have their own DNA that is similar to
prokaryotic DNA.
Have their own ribosomes that are similar in
construction to prokaryotic ribosomes.
Synthesize many, but not all, of their own
proteins.
 Mitochondria replicate by binary fission -
similar to prokaryotic cell division.

CYTOSKELETON
Scaffolding of proteins that transport
materials, position and move organelles,
maintain and change cell shape, and organize
enzymes into functional associations.
3 components - actin filaments,
microtubules, and intermediate
filaments.
All are polymers of smaller protein subunits -
lengthen through addition of polymer
subunits.

Actin filaments
- involved in cell movements and in membrane
deformations.
- smallest components of the cytoskeleton.
Microtubules
- hollow tubes made of proteins called tubulins
-responsible for cell movements and movements of
organelles within the cytoplasm, movement of
chromosomes during cell division.
- largest components of the cytoskeleton.
Intermediate filaments
- 8 stranded protein fibers.
- play a role in cell structure, anchoring organelles
and in transport of materials within the cytoplasm
anchor neighboring cells to each other in tissues.

CENTRIOLES
Are part of specialized region of the cell
called the centrosome (cell center) found
in animals and most protists.
The centrioles are involved in the
production of microtubules (mt).
Mt have many functions including moving
chromosomes during cell division.
Centriole structure - 9 triplets of
microtubules surrounding a hollow core –
centrosome similar to the basal body of
flagella.

Microbodies
 A microbodies are cytoplasmic organelles
which are more or less globular shaped and
contains degradative enzymes bound
within a single membrane.
 Microbodies are specialized as containers
for metabolic activity.
 These vesicles form through growth and
division within the cytoplasm.

Types: Peroxisomes and Glyoxisomes
Glyoxisomes are found in plants -
contain enzymes that convert fats into
carbohydrates.
Peroxisomes
derives their name from hydrogen peroxide.
- used for removing reactive compounds
from the cytoplasm.
– create H2O2 as a byproduct and degrade
it with the enzyme catalase.

Chloroplasts
 sites of photosynthesis - in nearly all plants
and some protists.
Trap light energy and convert it into chemical
energy.
The light energy trapping molecules of
photosynthesis are found in the membranes of the
thylakoids.

Structure
• The chloroplast is surrounded by two unit
membranes,
• The space between two membranes is called
periplastidal space.
• The internal structure shows two distinct
part:
(i) colourless ground substance called stroma
and
(ii) closed flat stack-like membrane system
called grana.

STROMA
 Stroma is watery and proteinaceous ground
substance.
 It contains ribosomes.
 A self-replicating DNA molecule is also
present in stroma.
 The dark reaction of photosynthesis takes
place in stroma.

GRANA
 Grana are densely packed stacks of
membrane layers called the thylakoids
found within the stroma
 Each thylakoid is bounded by a single
membrane but because of flatness of these
structures they appear as double membrane
layer surrounded or lamellae.

Grana
In these thylakoids the light reaction of
photosynthesis takes place.
Two adjacent grana are joined with one
another by lamellae called intergranal
lamellae or stroma.

 Chloroplasts have their own DNA, similar to
prokaryotic DNA.
 Can synthesize many of their own proteins
using prokaryote-like ribosomes
 Synthesize many, but not all, of their own
proteins.
 Replicate through division similar to
prokaryotic cell division.
 Chloroplasts can take on other functions
NB.

Other Plastids
Are a larger family of plant organelles.
All plastids including Chloroplast develop
from proplastids.
They contain the same genome as
chloroplasts but differs in structure and
function.
Differs from the Chloroplast because they
lack the thylakoid membrane system and
other components of the photosynthetic
apparatus.

The diff types of plastids are frequently
classified according to the kinds of pigments
they contain.
Chloroplast- they contain the pigment
cholorophyll.
Chromoplast- lacks chlorophyll but
contains carotenoids. They are responsible
for the yellow, orange and red colours of
some flowers and fruits.
Leucoplast are nonpigmented plastids .
egs are Elaioplast and amyloplasts.

VACUOLE
Plant Cells have, in addition to the collection of
organelles found in other groups, a central
vacuole.
The central vacuole is usually filled with water and
solutes.
A high solute concentration draws water into the
vacuole, expanding the vacuole and the cell.
Because plant cells are enclosed by a cell wall, the
expansion of the vacuole can exert pressure on the
cell without causing the cell to burst.

 Dfn- a space within a cell that is empty of
cytoplasm, lined with a membrane, and
filled with fluid.
Functions include:
 Isolating materials that might be harmful or
a threat to the cell
 Containing waste products
 Containing water in plant cells

 Maintaining internal hydrostatic pressure or
turgor within the cell.
 Maintaining an acidic internal pH.
 Containing small molecules.
 Exporting unwanted substances from the
cell.

INTERCELLULAR JUNCTIONS
Neighbouring cells in tissues , organs, or organ
systems often adhere, interact and
communicate thru direct physical contact.
Intercellular junctions facilitate this contact .
There are several types of intercellular
junctions.
1. Tight junctions.
2. Desmosomes.
3. Gap junction.

At Tight junctions, membranes of
neighbouring cells are pressed together
preventing leakage of extracellular fluid.
Desmosomes (anchoring jxns) fasten cells
together into strong sheets.
Gap junctions (communicating jxns)
provide cytoplasmic channels bn cells.

3.0 Cell Structure and function (2).pptx

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