Monday, November 14, 2011

Biology. Cell.

I've no idea why I'm posting this. Anyhoo, read and understand.

Cell Structure

Cytology- study of cell and its structure and components as seen under the microscope

Cell biology-study of all aspects of cell-structure, biochemistry, development and physiology

Cytoplasm: living part of the cell lying outside the nucleus but within the cell membrane.

Cell structures:
·         Cell membrane (Nageli and Kramer) –membrane covering the protoplast
§  Structure: thin elastic skin like membrane covering the cell.
Biochemical composition
a) phospholipids
b) Proteins
c) Carbohydrates-provide specificity
       D) cholesterol-fluidity
§  Fluid Mosaic Model of plasma membrane –Singer and Nicholson
a)Arrangement of lipids- phospholipid bilayer
b) Arrangement of proteins-
extrinsic- found on outer and inner side of bilayer
intrinsic- found inserted within the bilayer.
c) Arrangement of carbohydrates-attached to either lipids or proteins on the external surface only
§  Function of plasma membrane:
 a)Functions of membrane carbohydrates
 b)Functions of membrane proteins
 c) Transport across Membranes
 d) Passive Transport
        a) Diffusion
e) Active Transport
    a) Bulk transport
    b) Phagocytosis
    c) Pinocytosis
·         Endoplasmic Reticulum- (name given by Porter): Biosynthetic Factory
1. Structure:
        Composed of 3 types of units:
       2 types of ER:
o   Rough ER – With ribosomes and synthesizes proteins
o   Smooth ER–Without ribosomes and synthesizes steroids, lipids, carbohydrates and proteins
               2. Functions
§  Circulatory System of the cell
§  Protein Synthesis
§  Detoxification of drugs and other poisons
§  Membrane Factory
§  Storage of synthesized materials
§  Synthesis of molecules like bile acids, phospholipids, cholesterol and hormones

·         Golgi Apparatus-(Named after its discoverer Camillo Golgi) : Traffic Director

o   Function
§  Modification and packaging of proteins
§  Produces acrosome of sperm
§  Gives rise to lysosome
§  Helps in osmoregulation in one-celled fresh water animals via contractile vacuole
o   Structure
§  Group of flattened sacs placed one over another to form a pile/ stack.
§  Each stack is called a dictyosome
§  3 types of units in the Golgi Apparatus:
v  Cisternae
v  Tubules
v  Vacuole
·         Lysosomes- Discovered by Christian De Duve (Suicide Bags)
o   Found only in eukaryotic cells.
o   Contain hydrolytic enzymes/hydrolases
o   4 functional stages are observed:
§  Primary
§  Secondary
§  Auto lysosome
§  Residual body
o   Functions:
§  Intracellular digestion
§  Apoptosis
§  Acrosome
§  Absence of lysosomal enzymes may lead to Lysosomal storage diseases
·         Mitochondria – First seen by Kolliker (Powerhouses)
o   Structure:
§  2 membranes- inner is selectively permeable and is produced into a large number of folds called cristae
§  F0F1 Particles: stalked particles in cristae involved in ATP synthesis.
§  Mitochondrial Matrix
v  Mitochondrial DNA
v  Ribosomes
v  RNA
o   Functions:
§  Krebs Citric Acid Cycle
§  Electron Transport
·         Ribosomes (First seen by Albert Claude) ; RNA + Proteins= Ribosomes
o   Not found in : Mature RBC, mature sperm, sieve tube members of phloem in plants
o   S= Svedberg Unit or Sedimentation Coefficient
o   Prokaryotes: 70S
o   Eukaryotes: 80S
o   Mitochondrial Ribosomes: 55S to 80S
o   Chloroplast Ribosomes: 70S
o   Structure:
§  Composed of 2 units: Larger subunit and smaller subunit.
o   Functions: Protein Synthesis
§  Ribosomes attached to ER: Secretory proteins (mucus and digestive enzyme) synthesis
§  Free Ribosomes: Internal use proteins (chlorophyll, haemoglobin) synthesis
·         Centrioles
o   Found only in Animal Cell
o   Centrioles of a pair occurring at right angles to each other: Diplosome
o   Functions:
§  Microtubule organizing centre during cell division
§  In animal and lower plant cells, centrioles give rise to cilia and flagella. They’re called basal bodies.
·         Cytoskeleton
o   Microtubules
o   Microfilaments
o   Intermediate Filaments
·         Nucleus (Robert Brown) Master Organelle
o   Nuclear Envelope or Karyotheca
o   Nucleoplasm or Karyolymph
o   Chromatin (dispersed- -Eu, condensed –Hetero)
o   Nucleolus
o   Functions:
§  Responsible for the continuing of the life of the cell
§  Carries hereditary information in its chromosomes
§  Nucleolus: Ribosome Factory
Ultra structure of Plant Cell
§  Cell Wall
o   Middle Lamella- Calcium and Magnesium Pectate
o   Primary Wall-pectin and hemicellulose
o   Secondary Wall-High cellulose content
§  Plastids
o   Chloroplast
§  Stroma
§  Thylakoids
§  Stroma Lamellae
o   Leucoplast (Amylopast) : Formation and storage of starch grains
o   Chromoplast: Plastids responsible for yellow, red and orange color of many flowers and fruits
§  Vacuoles
o   Bubble like structure bound by a single membrane-Tonoplast
o   Contents of vacuole: Cell Sap
o   Functions:
§  Store organic compounds
§  Contain hydrolytic enzymes for macromolecule digestion
§  Store inorganic ions like K+ and Cl-
§  Store anthocyanin responsible for red and blue color in flowers
§  Helps in increasing cell size
§  Ergastic Substances
o    Reserve Food Materials
o    Secretory products

The End