Cell structure

CELL STRUCTURE

1. THE CELL
BY DR. SAKINA RUHI
MBBS, MD(BIOCHEMISTRY)
SENIOR LECTURER,DEPARTMENT OF
BIOCHEMISTRY,IMS, SHAHALAM

2. 2
OUTLINE
•Difference between prokaryotic & Eukaryotic cell .
•Difference between Animal & Plant cell
•Different cell organelles & Its function
•Cell Membrane
•Molecular movements & Cell-transport mechanism

3. 3
Cell Theory
•1. All living things are made of cells.
•2. New cells are produced from existing
cells
•3. Cells are the basic unit of structure
and function in living things.

4. 4
Prokaryotes vs. Eukaryotes
•Prokaryotes
(bacteria)

nucleus not well
defined
and very few

organelles.

•Eukaryotes
(protists,
fungi, plants and
animals) larger,more
complex,DNA is
inside the nucleus

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Plant Cells Vs. Animal Cells
•Only plant cells
contain:
•Cell wall
•Chloroplasts
•Large central
vacuoles
•Only animal
cells contain:
•Centrioles

6. 6

7. 7
CYTOPLASM
•Viscous fluid containing organelles
• components of cytoplasm
•Interconnected filaments & fibers
•Fluid = cytosol
•Organelles (not nucleus)
• storage substance

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Nucleus

9. 9
Nucleus
•Repository for genetic material
•Directs activities of the cell
•Usually single, some cells several,
• RBC none
•Contains
•Chromosomes
•Nucleolus

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Nuclear Envelope
•Separates nucleus from
rest of cell by two
phospholipid bilayer
membrane
Double membrane
Has pores

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Nucleolus
•Directs synthesis of RNA
• Nucleolus is mainly involved in
the assembly of ribosomes

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Endoplasmic reticulum
•Largest internal membrane
•Composed of Lipid bilayer
•Serves as system of channels from the nucleus
•Functions in storage and secretion
•Two types
•Rough endoplasmic reticulum
•Smooth endoplasmic reticulum

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Smooth Endoplasmic Reticulum
•No attached ribosomes
•Has enzymes that help
build molecules
•Carbohydrates
•Lipids

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Rough Endoplasmic Reticulum
•Ribosomes attached to the
surface
•Manufacture protiens
•Not all ribosomes attached
to rough ER
•May modify proteins from
ribosomes

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Ribosomes
•Ribosomes are RNA-protein complexes composed of
two subunits that join and attach to messenger RNA.
•site of protein synthesis
•assembled in nucleoli

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Golgi Apparatus
Packaging & shipping station
of cell
collect, pack, and distribute
molecules synthesized at
one location in the cell
and utilized at another
location

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HOW Golgi Apparatus Functions
1. Molecules come in vesicles
2. Vesicles fuse with Golgi
membrane
3. Molecules may be modified
by Golgi
4. Molecules pinched-off in
separate vesicle
5. Vesicle leaves Golgi apparatus
6. Vesicles may combine with plasma
membrane to secrete contents

19. 19

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Mitochondria
A. "Powerhouse of the
cell" - cellular
metabolism
B. Structure- outer and
inner membranes,
cristae
C. Have their own DNA

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Mitochondria
•Break down fuel molecules
(cellular respiration)
•Glucose
•Fatty acids
•Release energy
•ATP

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Lysosomes
•Contain digestive enzymes
•Functions
•Aid in cell renewal
•Break down old cell parts
•Digests invaders

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Cytoplasm
Phagocytosis
Food
vesicle
Golgi
apparatus
Lysosomes
Plasma
membrane
Digestion of
phagocytized
food particles
or cells
Endoplasmic
reticulum
Transport
vesicle
Old or damaged
organelle
Breakdown
of old
organelle
Extracellular
fluid
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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PEROXISOMES
Peroxisomes –are single
membrane cellular
organelle,also called
microbodies
Catalase and peroxidase:
the enzymes of
peroxizomes destroy
unwanted peroxides & other
free radicals

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Cytoskeleton
•Network of
protein
filaments
•Maintains shape
•Involved in cell
movement

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Cytoskeleton

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Cell Membrane
•Regulates what
enters and leaves
the cell and
provides support
and protection
•Structure – lipid
bilayer with
embedded proteins

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Membrane Proteins
1. Channels or transporters
•Move molecules in one
direction
2. Receptors
•Recognize certain
chemicals

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Membrane Proteins
3. Glycoproteins
•Identify cell type
4. Enzymes
•Catalyze production of substances

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TRANSPORT MECHANISM
classified into
 Passive Transport (i)simple diffusion
(ii)facilitated diffusion
(iii) ion exchange
 Active Transport
 Pumps –can drive molecules against the gradient using
energy

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Simple Diffusion
Particles move from an area of high
concentration to an area of lower
concentration
No energy is required
very slow

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Osmosis
•Diffusion of water through a
selectively permeable membrane

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Facilitated Diffusion
•Molecules move through protein
channels.
•Carrier mediated process
•No energy required

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ION CHANNELS
•Membrane have special devices called ion channels
•For quick transport of Na +,K+ ,Cl + and Ca ++
•They remain close and open on response to stimulus
•They are also called as gated channels
•Important for nerve impulse propogation,synaptic
transmission

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Active Transport
•Carried our by protein pumps found in
the membrane
•Energy is required

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Active Transport
•Molecular movement
•Requires energy (against gradient)
•Example is sodium-potassium pump

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Endocytosis
•Cell takes material into cell by infolding of the cell
membrane
•Phagocytosis – eating – cell engulfs large particles
•Pinocytosis – drinking – cell takes in liquid

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Process of Endocytosis•Plasma membrane surrounds material
•Edges of membrane meet
•Membranes fuse to form vesicle

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Exocytosis
•Cell releases large
amounts of material

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Transport system
•Classified as Uniport , Symport and Antiport
•UNIPORT-Carries single solute across the membrane e.g –
glucose transporter in most cells ,calcium pump
•CO TRANSPORT –If transfer of one molecule depend on
simultaneous transfer of another molecule.
• (i)SYMPORT (ii) ANTIPORT

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•SYMPORT-Transporter carries two solutes in same
direction .
•eg-sodium dependent glucose transport
•ANTIPORT –Carries two solutes or ions in opposite
direction
• eg sodium pump,sodium bicarbonate exchange in RBC

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