Cell

Lecturer, Department of Pharmacy
East West University

Amoeba Proteus
Plant Stem
Red Blood Cell
Nerve Cell
Bacteria

The cell is the smallest unit of life.
Microorganisms such as bacteria, yeast, and
amoebae exist as single cells.
By contrast, the adult human is made up of about 30
trillion cells which are mostly organized into
collectives called tissues.

Cells are nothing but some compartments…
Eukaryotic cells are the membrane bound
compartments!!!

• Prokaryotic
&
• Eukaryotic

Do not have structures
surrounded by
membranes
Few internal structures
One-celled organisms,
Bacteria

Contain organelles surrounded by membranes
Most living organisms
Plant Animal

Why don’t we find any giant
amoeba or bacteria???

Study of the structure and
function of
eukaryotic cells

Organelle means
“little organ”
Found only inside
eukaryotic cells
All the stuff in
between the
organelles is cytosol
Everything in a cell
except the nucleus is
cytoplasm

Outer membrane of cell
that controls movement
in and out of the cell
Made of a phospholipid
bilayer

1. lipids
2. functional proteins
3. carbohydrates

1. Membrane Lipids (42% of its weight)

Double layer of phospholipid molecules:
hydrophilic heads
—toward watery environment, both sides
hydrophobic fatty-acid tails
— inside membrane
barrier to ions and water soluble compounds

Integral proteins:
within the membrane
Peripheral proteins:
inner or outer surface of the membrane

1. Anchoring proteins (stabilizers):
– attach to inside or outside structures
2. Recognition proteins (identifiers):
– label cells normal or abnormal
3. Enzymes:
 catalyze reactions
4. Receptor proteins:
– bind and respond to ligands (ions, hormones)
4. Carrier proteins:
– transport specific solutes through membrane
4. Channels:
– regulate water flow and solutes through membrane

1. Proteoglycans and glycoproteins
2. Glycolipids
extend outside cell membrane
form sticky “sugar coat” (glycocalyx)

1. Lubrication and protection
2. Aids attachment of cells
3. Specificity in binding (receptors) e.g. antigens and
enzymes
4. Cell-cell recognition and interaction

1. cytosol (fluid):
 dissolved materials:
 nutrients, ions, proteins, and waste products
2. organelles:
 structures with specific functions
All materials inside the cell and outside the
nucleus

Difference between cytosol and extracellular fluids:-
1. Conc. of K+
is high in cytosol
2. Conc. of Na+
is high in extracellular fluids
3. Suspended protein is high
4. Reserve small quantity of carbohydrates and amino acids
(extracellular fluid is carrier only)
Both cytosol and extracellular fluids (interstitial fluid) contain
insoluble materials. In case of cytosol, these masses are known as
inclusions.
Ex. Cytosol:- Glycogen granules, lipid droplets, pigment granules
Extracellular fluids:- Melanine in skin, Mineral deposit in bone

Nonmembranous organelles:
no membrane
direct contact with cytosol
 Membranous organelles:
covered with plasma membrane
isolated from cytosol

6 types of nonmembranous organelles:
1. cytoskeleton
2. microvilli
3. centrioles
4. cilia
5. ribosomes
6. proteasomes

Structural proteins for shape and strength
It functions as the cells skeleton.
I. Microfilaments
II. Intermediate Filaments
III. Microtubules
IV. thick filaments (muscle cells)
Cytoskeleton includes
It provides an internal
protein framework that
give cytoplasm
strength and flexibility

Actin
Microtubules
Intermediate
filaments

Micro (Thin) filaments composed of
the protein called actin:
1. Anchor the cytoskeleton to
integral protein of plasma
membrane (provide additional
mechanical strength)
2. interact with other proteins for
consistency of the cytoplasm
3. Pairs with thick filaments of
myosin for movement of a
portion or to change the shape of
entire cell.
smallest of the cytoskeletal elements (6 nm in diameter)

 Mid-sized between
microfilaments and thick
filaments ( 7- 11 nm)
most durable
cytoskeletal elements
1. strengthen cell and
maintain its shape
2. stabilize the position of
the organelles
Protein composition varies from cell to cell

Large, hollow tubes of tubulin
protein:
1. strengthen cell and anchor
organelles
2. change cell shape
3. move vesicles within cell
(affected by molecular motor-
kinesin and dynein)
4. form spindle apparatus
5. Form structural componant (e.g
centrioles and cillia)
Largest components
# change over time
Form by tubuline
molecule

Increase surface
area for
absorption
Attach to
cytoskeleton

Centrioles form spindle
apparatus during cell
division
Centrosome: cytoplasm
surrounding centriole
Nine triptels
Not present in RBC, skeletal muscle
cells, cardiac muscle cells, nerve cells

Cilia move fluids across
the cell surface
• Found in Lungs, reproductive tracts.
• It can “beat” rhythmically.
Relatively long, slender extension of plasma membrane.

5. Ribosomes
• Build polypeptides in protein synthesis
• Two types:
– free ribosomes in cytoplasm:
• proteins for cell
– fixed ribosomes attached to ER:
• proteins for secretion
60% RNA + 40% protein, 25 nm in diameter
• # vary cell to cell (contrast: liver cell/adiposites)
• Two sub-unit (large and small)
• rRNA

For protein synthesis, two subunit must join together with mRNA

Proteasomes
Ubiquitin ( a molecular tag)
• Contain enzymes (proteases)
• Remove and break down damaged or abnormal
proteins
( Disassemble damaged proteins for recycling)
• Require targeted proteins to be tagged with
ubiquitin

Membranous Organelles
• 5 types of membranous organelles:
1. Endoplasmic reticulum (ER)
2. Golgi apparatus
3. Lysosomes
4. Peroxisomes
5. Mitochondria

endo = within
plasm = cytoplasm
reticulum = network
Endoplasmic Reticulum (ER)
Cisternae are storage chambers
within membranes
• Forms cisternae
• Rough ER (RER) contains ribosomes
– Form transport vesicles
• Smooth ER (SER)
– Involved in lipid synthesis
Intracellular membranes
involved in synthesis, storage,
transportation and detoxification

Functions of ER
1. Synthesis of proteins, carbohydrates, and lipids
2. Storage of synthesized molecules and materials
3. Transport of materials within the ER
4. Detoxification of drugs or toxins

Smooth Endoplasmic Reticulum (SER)
• No ribosomes attached
• Synthesizes lipids and carbohydrates:
– phospholipids and cholesterol (membranes)
– steroid hormones (reproductive system)
– glycerides (storage in liver and fat cells)
– glycogen (storage in muscles)
- store Ca+2
- detoxification of drugs

Rough Endoplasmic Reticulum (RER)
Surface covered with ribosomes:
1. active in protein and glycoprotein synthesis
2. folds polypeptides into protein structures
3. encloses products in transport vesicles
Workshop and shipping depot

Golgi Apparatus
Vesicles enter forming face and exit maturing face

Carry materials to and from Golgi apparatus

Ejects secretory products and wastes

Powerful enzyme-containing vesicles:
lyso = dissolve, soma = body

Primary lysosome:
formed by Golgi and inactive enzymes
Secondary lysosome:
lysosome fused with damaged organelle
digestive enzymes activated
toxic chemicals isolated

Clean up inside cells:
1. break down large molecules
2. attack bacteria
3. recycle damaged organelles
4. ejects wastes by exocytosis

1. lysosome membranes break down
2. digestive enzymes released
3. cell decomposes
4. cellular materials recycle
auto = self, lysis = break
Self-destruction of damaged cells (Apoptosis):

 break down fatty acids, organic compounds produce
hydrogen peroxide (H2O2).
 Peroxisomes harbor enzymes that rid the cell of
these toxic peroxides.
 replicate by division
Are enzyme-containing vesicles:
Carry enzymes that neutralize toxins

Have smooth outer
membrane and folded inner
membrane (cristae)
Matrix: fluid around cristae

Mitochondrion takes chemical energy from food
(glucose):
produces energy molecule ATP
Figure 3–9b

Aerobic metabolism (cellular respiration):
mitochondria use oxygen to break down food and
produce ATP
glucose + oxygen + ADP → carbon dioxide + water + ATP
•Glycolysis:
– glucose to pyruvic acid (in cytosol)
•Tricarboxylic acid cycle (TCA cycle):
– pyruvic acid to CO2 (in matrix)
The Reactions

It is the cell’s control center
• Largest & most conspicuous structure in a cell
• Only visible organelle under light microscope
Store all information to direct synthesis
of diff. 1,00,00 proteins.
It determine -
• structure of the cell
• what function it will perform
Most cells have single
nucleus
Exception-
Muscle cells - polynucleated
RBC- non-nucleadted

Nucleolus: Dark staining area
(made of - RNA,enzymes & histone)
Synthesize rRNA. Prominent in liver
cell (why?)
Nuclear envelope: double
membrane around the nucleus
Nuclear pores:
communication
passages
Perinuclear space: between
2 layers of nuclear envelope
Nucleoplasm: fluid
containing ions,
enzymes, nucleotides,
and some RNA
• Nuclear matrix:
‒ support filaments
DNA: all information to
build and run organisms

Vital Statistics of Human Genome

Gene: DNA instructions for 1
single protein

The chemical language of DNA instructions:
sequence of bases (A, T, C, G)
triplet code:
3 bases = 1 amino acid

Transcription:
copies instructions from DNA to mRNA (in nucleus)
Translation:
ribosome reads code from mRNA (in cytoplasm)
assembles amino acids into polypeptide chain

Processing:
by RER and Golgi apparatus produces protein

A gene is transcribed to mRNA in 3 steps:
gene activation
DNA to mRNA
RNA processing

Uncoils DNA, removes histones
Start (promoter) and stop codes on DNA mark
location of gene:
coding strand is code for protein
template strand used by RNA polymerase molecule

Enzyme RNA polymerase transcribes DNA:
binds to promoter (start) sequence
reads DNA code for gene
binds nucleotides to form messenger RNA (mRNA)
mRNA duplicates DNA coding strand, uracil replaces
thymine

At stop signal, mRNA detaches from DNA molecule:
code is edited (RNA processing)
unnecessary codes (introns) removed
good codes (exons) spliced together
triplet of 3 nucleotides (codon) represents one amino
acid

mRNA moves:
from the nucleus
through a nuclear pore

mRNA moves:
to a ribosome in cytoplasm
surrounded by amino acids

mRNA binds to ribosomal
subunits
tRNA delivers amino acids to
mRNA

tRNA anticodon binds to mRNA
codon
1 mRNA codon translates to 1
amino acid

Enzymes join amino acids
with peptide bonds
Polypeptide chain has
specific sequence of amino
acids

At stop codon,
components separate
Stop Codons
In RNA:
UGA: "U Go Away"
UAA: "U Are Away"
UAG: "U Are Gone“
In DNA:
TAG: "They Are Gone"
TAA: "They Are Away"
TGA: "They're Going Away"

Direct control through synthesis of:
structural proteins
secretions (environmental response)
Indirect control over metabolism through enzymes

Cell division is the reproduction of cells
Apoptosis is the genetically controlled death of cells
Mitosis is the nuclear division of somatic cells
Meiosis produces sex cells
cell division
The Cell Life Cycle

Most somatic cells spend the majority of their lives in
this phase
Interphase includes
G1
S
G2
Interphase
The Cell Life Cycle

The structure of a chromosome after DNA Replication

Prophase
Metaphase
Anaphase
Telophase
During cytokinesis, the cytoplasm divides and
cell division ends
Mitosis

 The chromosomes are in an extended form and seen as
chromatin in the electron microscope.
 The nucleus is visible
Interphase

 The chromosomes are seen to consist of two chromatids joined
by a centromere.
 The centrioles move apart toward opposite poles of the cell.
 Spindle fibers are produced and extend from each centrosome.
 The nuclear membrane starts to disappear.
 The nucleolus is no longer visible.
Prophase

 The chromosomes are lined up at the equator of the cell.
 The spindle fibers from each centriole are attached to the
centromeres of the chromosomes.
 The nuclear membrane are disappeared.
Metaphase

The centromere split, and the sister chromatids separate
as each is pulled to an opposite pole.
Anaphase

Telophase
 The chromosomes become longer, thinner, and less distinct.
 New nuclear membranes form.
 The nucleolus reappears.
 Cell division is nearly complete.

Interphase, Mitosis, and Cytokinesis

Cell

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