CELL BIOLOGY -2

 BIOMOLECULES AND THE CELL

90%   of  living  matter  made  of  C,H,O,N,S,P  AND  10%  is composed of C,H,O,N,S,P & 10%  is composed  of  K , Ca , Na ,Mg , Cl , F, I , Fe , Zn , Mo , Se , Cu , Co. 

Among  these   carbon  plays  a  very  important  role because  of  its  tetravalency,  isomerism  and  covalent bond  forming  capacity.

E.coli has 6000 types  of  organic compounds and  a  human  cell  has 1 lakh types of  organic molecule.

MICROMOLECULE	MACROMOLECULE	FUNCTIONS
PROTEINS	AMINO ACIDS	BASIS OF STRUCTURE AND FUNCTION(STATIC AND DYNAMIC).
DNA	DEOXYRIBONUCLEOTIDES	REPOSITORY OF GENETIC INFORMATION
RNA	RIBONUCLEOTIDES	PROTEIN BIOSYNTHESIS
POLYSACCHARIDES	MONOSACCHAARIDES	SHORT TERM ENERGY
LIPIDS	FATTY ACIDS AND  GLYCEROL	LONG TERM ENERGY

Simple   inorganic   molecules  form  bio micromolecules. The   latter  form  biomacromolecules. These  inturn  form   supra-molecular  assemblies,  which  are  required  to  form the cell organelles , their membranes  and  the  cytosol.

All  the organelles  form a cell. Cells  aggregate  to form tissues. These  then  form  organs .Organs  form  organ  systems  which  coordinate  to  regulate  the  organism.

For  a 65 kg man, the body is comprised of  the  following:

40 kg	60%	Water
11 kg	17%	Proteins
9 kg	13.8%	Lipids
1 kg	1.5%	Carbohydrates
6.1 kg	4%	Minerals.

Cell   is  the  structural  and  functional  unit  of  life. The  organelles  of  a   cell  can  be  easily  isolated  by  differential  centrifugation.

Prokaryotic cell	Eukaryotic cell
1 to 10 micron.	10 to 100 micron.
Well defined nucleus absent	Well defined nucleus present.
Nuclear envelope absent	Nuclear envelope present
Most cell organelles  absent	All  cell  organelles  present.
Primitive	Advanced

Cell  organelles :-

       

       A. Nucleus:-

§  Largest  cell  organelle.

§  Double  membrane  envelope.

§  Outer  memrane  is  connected  with  e.r.

§  Nuclear  pores  (diameter= 900 nm.)

§  DNA– repository  of  genetic  information.

§  RNA-  protein biosynthesis.

§  Eukaryotic  dna :  histone  proteins =  1:1.

§  DNA+ histones  = nucleosomes.

§  1  chromosome  has  millions  of  nucleosomes.

§  46  chromosomes  in  human  genome.

§  Nucleus  has  nucleolus  rich  in  RNA.

§  Nucleoplasm  is  rich  in  enzymes  like  DNA polymerases  and  RNApolymerases.

B. Mitochondria:-

§  Mitos- thread ,  chondrus – granule.

§  Power  house  of  cell.

§  Various  shapes  andv sizes.(dimension =  1 × 3 μm).

§  Double  membrane  system.

§  1- 5 th  of cell  volume  covered  by  2000 mitochondria.

§  Outer  membrane – soft  and  continuous.

§  Inner  membrane   -  cristae  formation.

§  Matrix  of  mitochondria  is  called  mitosol.  It  has  chemicals  like  flavoproteins, cytochromes b, c1, c, a, a3 .(useful  in  electron  oxidation chain  and  oxidative  phosphorylation.)

§  Reactions  like  biomolecule  metabolism,  beta  oxidation ,  citric  acid   cycle, ATP production,  heme  and  urea  synthesis  occurs  in  matrix. 

§  The  inner  membrane  contains  coupling  factors.

            §  Mitochondria  has  its  own  DNA, RNA,  proteins. 

§  It prepares  its  own  proteins(10% of  total  cell  protein). 

§  Aerobic  prokaryotes  evolved  into  mitochondria  which  then  lived  with  symbiosis  with  anaerobic  eukaryotes  . These  later  evolved  into  aerobic  eukaryotes.

C. Endoplasmic  Reticulum:-

§  Smooth endoplasmic reticulum (S.E.R)

                -    calcium ion supply.

          -     drug  metabolism.

           -  lipid  synthesis.  (triacylglycerol, phospolipids, sterols .)

§ Rough endoplasmic reticulum(R.E.R) -  granular  in appearance.

{R.E.R – associated with the factories of protein biosynthesis(ribosomes).}

 E.R – disrupts to form microsomes during cell fractioning.

  D. Golgi  apparatus :-

• Dictyosomes(unique cluster of membrane vescicles)  modify  to form  golgi complex.
• It  modifies  protein  by  adding  carbohydrates , lipids or sulphate  moeities  to  the  polypeptide  chain.
• Involved  in  membrane  synthesis  of  organelles  like peroxisomes  and  lysosomes.

        E. Lysosomes :-

• Single  membrane.
• Digestive   tract  of  cell.
• It’s  enzymes -  hydrolases –  α- glucosidases,  cathepsins , lipases , ribonucleases.
• These  maintain  the  dynamics  of  cellular  components.
• Lipofuscin  -  wear  and  tear  pigment  or  age  pigment  accumulate  in  cell .  Cells  rich  in   lipofuscin  need to  be  destroyed  by the  post- mortem  autolysis.

       F. Peroxisomes:-

§ Also  called  microbodies.

§ Single  membrane.

§ Oval  to  round.

§ Contain  enzyme  catalase -  breakes  hydrogen  peroxide  into  water  and oxygen.

§ Also  oxidises  long  chain  fatty  acids.

§ Synthesizes  plasmalogens  and  glycolipids.

§ In  plants , called  glyoxisomes  - do  glyoxylate  pathway.

§ Peroxisome  biogenesis  disorders  have  high   amount  of  c-24  to  c-26  and  less  plasmalogens.

§ Its  sincere  case  is  zellweger  syndrome  -  death within  one  yr  after  birth.(absence  of  functional  peroxisomes).

G. Cytosol  and  cytoskeleton:-

§             Cytosol  = cell  matrix  -  it  has  enzymes,  metabolites,  electrolytes  in  aqueous.

§             Cytoskeleton = complex  network  of  protein  filaments 

§             It   has  microtubules  ,  actin  filaments,  intermediate  filaments.