Transcript Document

CELL STRUCTURE
Common Features of Cells
 All have plasma membrane (cell membrane)
 All have nuclear region
 All have cytoplasm
cytoplasm
nuclear
region
cell
membrane
STRUCTURE OF CELL MEMBRANE
The cell membrane has a two-layered structure mainly made of
protein, lipid and carbohydrate molecules
 Protein molecules are embedded in the lipid bilayer
 Carbohydrate molecules may branch out from the external
surface of the membrane
 Carbohydrate chains bonded to lipids form glycolipids
 Carbohydrate chains bonded to proteins form glycoproteins
Lipid bilayer
STRUCTURE OF CELL MEMBRANE
Fluid – Mosaic Model of Cell Membrane: (by Singer and Nicholson)
CARBOHYDRATES
G
PROTEINS
G
L
L
Y
Y
C
C
O
O
L
P
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R
P
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T
D
E
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N
PHOSPHOLIPIDS
• Proteins in the cell membrane do several different
functions.
PROTEINS OF CELL MEMBRANE
Transport Proteins: Control the movement of substances
through the cell membrane
Receptor proteins: They bind with messenger molecules to
begin or stop metabolic activities
Enzymes:
Catalyze reactions
Structural proteins: Help bind the membrane to neighboring
cells or structural elements in the
cytoplasm
Identity proteins:
Distinguish the cell from other cells
Proteins of Cell Membrane
Selective permeability enables the cell to
protect the inner balance (homeostasis).
The molecules that can
pass EASILY through the
cell membrane
• Small molecules such as
–
–
–
–
–
–
Water
Oxygen
Carbon dioxide
Glucose
Amino acids
Urea
• Molecules that can
dissolve lipids such as
– Alcohol
– Ether
The molecules that
CANNOT pass through
the membrane
• Polymers
• Electrically neutral molecules enter and leave cells more
easily than electrically charged ions.
• In animal cells (+) ions can pass easier than (-) ions.
• Lipid molecules (fatty acids, glycerol) pass through cell
membranes easily.
• Fat soluable vitamins (A, D, E,K) can pass easier than
water soluable vitamins.
 Prevents the cell contents from interacting
with the surrounding medium
 Gives shape and mechanical strength to
the cell
 Controls the material transport
CYTOPLASM AND ORGANELLES
• Cytoplasm:
– Fluid-filling part of the cell
– Occupies the space between the membrane
and the nucleus
– Includes the cytoskeleton, organelles and
cytosol.
– 65-95% water
– Contains many substances (granular proteins
mostly)
– Also contains carbohydrates, lipids, enzymes,
minerals, vitamins and pigments
CYTOPLASM AND ORGANELLES
CYTOPLASM AND ORGANELLES
• Organelles: In eukaryotic cells there are
secondary compartments covered with cell
membrane. These are called organelles.
• An organelle is the part of the cell which is
responsible for a specific function.
CYTOPLASM AND ORGANELLES
• Cytoskeleton:
– is the skeleton of the cell
– an interconnected system of protein fibers
and thin strands
– gives cells their shape and internal
organization
– composed of microtubules and microfilaments
CYTOPLASM AND ORGANELLES
Cytoskeleton:
• Microtubules are
linked in parallel rows.
• In animal cells
microfilaments are
found. They play role
in muscle contraction.
CYTOPLASM AND ORGANELLES
The cytoplasm of a eukaryotic cell includes the following organelles:
• ribosome
• endoplasmic reticulum
• mitochondrion
• Golgi bodies
• lysosome
• peroxisome
• vacuole
• plastids
• centrosome
RIBOSOME
•
•
•
•
Tiny, granular structures
Found in all cells without any exception
Made of RNA and protein
Some are found freely in cytoplasm and
some are attached to the ER
• Ribosomes are produced in nucleolus
RIBOSOME
Function: Proteins synthesis
 Ribosomes are made of two subunits
 Bacterial cells have smaller ribosomes.
When there is no protein synthesis in the cell
these subunits are separate from each other.
They come together in order to be functional.
ENDOPLASMIC RETICULUM
ENDOPLASMIC RETICULUM
ENDOPLASMIC RETICULUM
• Made of cell membrane
• Found in all cells except red blood cells
and bacterial cells
• Two types:
– Smooth ER (no ribosomes on it)
– Rough ER (ribosomes on the outer surface)
ENDOPLASMIC RETICULUM
Functions:
 carries proteins to Golgi body
 provides a pathway for the transport of
molecules throughout the cell
 smooth ER synthesizes lipids
 provides support to the cell
 divides the cytoplasm into compartments
(different type of chemical reactions can take
place at the same time)
 plays role in the contraction of skeletal
muscles
MITOCHONDRIA
MITOCHONDRIA
• is the place where aerobic cellular respiration
takes place in eukaryotic cells
• surrounded by double-layered membrane
• inner membrane has foldings called cristae,
which provides a large surface area for the
chemical reactions
• the fluid that fills the interior space is called
matrix
• matrix includes ribosomes, DNA, RNA and
proteins
• can duplicate itself
Golgi Body (Golgi apparatus)
Golgi Body
Consist of a stack of flat,
membrane –enclosed sacs and
small vesicles
Present in all cells except
blood and sperm cells
Plant cells have more golgi
than animal cells
They have connections with
the membranes of E.R.
Golgi Body
Functions of golgi:
 Secretion
Modifiying the molecules like
glycoproteins and glycolipids
coming from the E.R, and
releasing them to cytoplasm.
The vesicles originating from
the golgi moves towards the cell
membrane and the cell mebrane
expands.
It forms lysosomes.
Some vacuoles are formed by
golgi.
Helps formation of cell wall in
plants.
Golgi bodies are
highly developed
in gland cells.
For ex, their
number is very
high in salivary
glands. Gastric
glands and cells
which produce
nectar in plants.
Lysosome
They are spherical structures
surrounded by a single
membrane.
They are formed by golgi.
They contain hydrolytic
(digestive) enzymes.
When lysosomes burst and release these enzymes, the cell
starts to digest itself. It is called autolysis.
Mostly found in animal cells that make phagocytosis. For
ex; humans white blood cells.
Lysosome
Functions:
They digest intracellular and
extracellular molecules.
They digest worn –out cell
organelles.
They function in defence of
the cell.
They are found at the head
part of the sperm cells and let
sperms hydrolizye the outer wall
of the egg.
Lysosome
Functions:
They function in defense of
the cell. For ex; white blood
cells contain high no. of
lysosomes
They are found at the head
part of the sperm cells and let
sperms hydrolyze the outer wall
of the egg.
Peroxisome
They bud from the membranes of E.R.
As a result of breaking down amino acids and fatty
acids, a highly toxic molecule, H2O2 (hydrogen peroxide)
is produced.
Peroxisomes contain catalase enzyme that breaks
down H2O2.
They are especially found in liver, heart and muscle
cells in humans.
Vacuoles
They are fluid filled organelles surrounded with single
membrane.
Minerals, waste products, nutrients and some
pigments are stored in vacuoles.
They are found both in animal and plant cells, but
animal cells have smaller vacuoles than plant cells.
The immature plant cells have small vacuoles. As the
plant cell matures merge to form one big vacuole.
Vacuoles
There are three types of vacuoles:
1. Digestive vacuole:
Found in unicellular organisms and white blood cells.
They are formed when a food molecule is taken into
the cell and it’s surrounded by the cell membrane.
Vacuoles
2. Contractile vacuole:
Found in unicellular organisms that live in fresh water.
For ex:Paramecium
They pump out the excess water that goes inside the
organism.
@
Vacuoles
3. Storage vacuole:
 In plants, toxic waste
materials are stored in
storage vacuoles.
They also store some
pigments that give color
to plant parts.
PLASTIDS
They are found only in plant cells!!!
They are surrounded by double membrane.
There are three types of plastids:
Chloroplasts
Leucoplasts
Chromoplasts
Chloroplast
Outer membrane
Inner membrane
Grana
Stroma
 They contain the green pigment chlorophyll.
 Chlorophyll converts the light energy into chemical energy
(photosynthesis).
Chloroplast
Chloroplast
Outer membrane
Inner membrane
Grana:
 Formed with the
foldings of thylakoid
membranes
 Include the
chlorophyll pigment
Stroma:
 Fluid-filling part
 Include enzymes,
DNA, RNA, ribosomes
and other organic
molecules
Chloroplast
The main function of chloroplasts is photosynthesis.
They convert light energy into chemical energy and
store it in ATP.
But the ATP produced in the chloroplasts never get
out of this organelle. They are used in photosynthesis
only.
Chromoplast
 They contain different color pigments that give red, yellow,
orange color to different parts of plants.
 These pigments do not play role in photosynthesis.
 They are sensitive to light.
 When chloroplasts are exposed to sunlight they can turn
into chromoplasts. (Ex. Green tomato
Red tomato)
Leukoplasts
Leucoplasts:
They are usually located at
tissues that are not exposed
to sunlight (ex: roots)
They store starch, oil and
other plant products.
Ex:Potato
starch
Corn
lipid
Bean
protein
They can turn into
chloroplast when they are
exposed to light.
Potato
Centrosome
 made up of two perpendicular
cylinders called centrioles
 contains microtubules
located near the nucleus
 function in cell division
 they produce spindle fibers
which moves the chromosomes
during cell division
 plant cells don’t have
centrosomes
Cell Wall
 plants, fungi, algae and bacteria have cell wall
 is not alive
 main function: protects the cell, gives its shape, gives
mechanical support
Bacteria
Ribosome
E.R.
Mitochondrion
Golgi body
Lysosome
Peroxisome
Central vacuole
Plastids
Centrosome
Cell mambrane
Cell wall
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Protists
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Only
contractile
vacuole
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-
Fungi
Plants
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Animals
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Digestive
vacuole
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-
Nucleus
DNA is located in nucleus in a eukaryotic
cell.
usually cells have one nucleus.
Bacteria, and mature red blood cells do
not have nucleus.
control center for cell metabolism and
reproduction
 if it is removed the cell dies
Experiments on nucleus
A
An ameba
cell
B
C
The cell is
divided into two
as shown
I
The cell is
divided into two
as shown
The nucleus of
the cell is
removed
I
II
Ameba
(lives)
D
I dies
II lives
II
Both cells die
because
nucleus is
destroyed
The cell
dies
The Structure of a Nucleus
The Structure of a Nucleus
The nucleus has three main parts:
Nuclear membrane
Nucleoplasm (contains chromatin)
Nucleolus
1. The nuclear membrane:
-
it is a double membrane which isolates
the nucleus
it has connection with the membrane of
ER
it has pores that provide the passage of
mRNA and some proteins
1. The nuclear membrane:
2. Nucleoplasm:
- fluid – filling part of the nucleus
- includes water, protein, DNA, RNA,
minerals and nucleotides
3. Nucleolus (pl.Nucleoli):
- dense mass of irregular size and shape
- produces ribosomes and involved in protein
synthesis
- the cells which have a high metabolic rate have
more nucleoli than the others
nucleolus
Histones
Coiling starts
Chromatin
strands
It is not visible
under light
microscope (cannot
be seen before and
after cell division)
Chromatin
Chromosome
It is visible under
light microscope
only during cell
division
Relationship between mitochondria and chloroplast
light energy
Chloroplast
CO2 + H2O
Glucose + O2
Mitochondria
ATP (for cellular work)
Comparison of Mitochondria and Chloroplast
Mitochondria
Chloroplast
DNA,RNA,
Ribosome
Double
membrane
Chlorophyll




X

ATP for
cellular
activities

X