Cell structure

THE CELLBY DR. SAKINA RUHI

MBBS, MD(BIOCHEMISTRY)

SENIOR LECTURER,DEPARTMENT OF BIOCHEMISTRY,IMS, SHAHALAM

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OUTLINE

• Difference between prokaryotic & Eukaryotic cell .

• Difference between Animal & Plant cell

• Different cell organelles & Its function

• Cell Membrane

• Molecular movements & Cell-transport mechanism

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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.

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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

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CYTOPLASM

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

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Nucleus

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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

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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

PhagocytosisFood

vesicleGolgi

apparatus

Lysosomes

Plasmamembrane

Digestion ofphagocytizedfood particles

or cells

Endoplasmicreticulum

Transportvesicle

Old or damagedorganelle

Breakdownof old

organelleExtracellularfluid

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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 Proteins3. Glycoproteins

• Identify cell type

4. Enzymes • Catalyze production of substances

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TRANSPORT MECHANISMclassified 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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