Cell and its biochemical organization-
CELL-
Definition:
Cell is the structural and functional unit of all living organisms.
Two types of cells:
Prokaryotes.
Eukaryotes.
PROKARYOTES
EUKARYOTES
Do not carry well developed nucleus.
Eg: Bacteria,
Ameoba,
Clamydomonas.
Well developed nucleus
Simple celled
Multicellular.
Do not have sub-cellular organelles.
Have sub-cellular organelles (Mitochondria, Golgi
apparatus, Ribosomes, Cytoplasma, Endoplasmic
Reticulum, Peroxyzomes.
Cell constituents are:
1. Plasma membrane.
2. Mitochondria.
3. Endoplasmic reticulum.
4. Golgi apparatus.
5. Lysozomes.
6. Peroxysomes.
7. Nucleus.
8. Cytoplasm.
Cell Constituents
Explanation
Function
PLASMA MEMBRANE
Outer most covering of the cell.
Made up of proteins, lipids and
carbohydrates.
Lipids present in plasma membrane
is phospholipid.
Lipids are bilayered.
Phospholipid have head and tail
region. Head is hydrophilic polar
and tail is hydrophobic non-polar.
Sometimes glycolipids and
cholesterol are also present in the
plasma membrane.
It resembles like fluid mosaic
Transport of ions (ca+, Na+, K+,
Biomolecules, glucose).
Carry receptors for hormones and
neurotransmitters.
model.
Proteins two types, one is extrinsic-
outside of plasma membrane.
Other is intrinsic- Inside of plasma
membrane.
MITOCHONDRIA
Power house of the cell.
Double membrane structure.
Inner membrane folded in the form
of cristae.
Centre part is called as matrix.
ATP synthesis.
Electron transport chain occurs in
inner membrane.
Oxidative phosphorylation occurs and
it is also a Part of urea cycle and heme
synthesis.
ENDOPLASMIC
RETICULUM
Tubular in structure.
Two types, Rough ER and Smooth
ER.
Due to presence of Ribosomes
Rough ER is named so.
RER- Protein synthesis and secretion.
SER- Steroid hormones, Phospholipids
has been synthesized.
Metabolism of various forms of
compounds takes place.
GOLGI APPARATUS
Tubular in shape.
Present almost in all cells in our
body (250 types of cells).
Matured RBC do not contain
mitochondria and golgi apparatus.
Important role in post-transcriptional
modification.
Sorting of proteins.
Export of proteins.
LYSOZOMES
Vesicular organelles (mostly round
like).
Formed from golgi apparatus.
Membrane of lysozomes has more
thickest membrane.
Carry hydrolytic (Important role in
destruction) enzymes.
Intra cellular digestion of
Macromolecules (Carbohydrates,
Lipids, Nucleic acids, Proteins).
Sucidal bags.
Destruction of bacteria.
Hydrolysis of nucleic acid, protein,
glycosaminoglycans, glycolipids,
sphingolipids.
PEROXYSOMES
Resemble like lysosomes.
Synthesized from either SER/ from
pre-existing peroxysomes.
Carry peroxidase enzyme, catalyse
enzyme etc.
These enzymes play important role in
detoxification.
Metabolism of peroxide and oxidation
of long chain fatty acids.
NUCLEUS
Nucleolus (Site for DNA replication
and transcription), chromatin
(Thread like structure).
Germ cells reproduce somatic
cells= mitosis and do not
reproduce.
Spherical in shape.
Covered by nuclear membrane.
Storage of DNA, replication and repair
of DNA, transcription and post-
transcriptional processing.
Nucleolus present inside the nucleus
helpful in synthesis of rRNA and
formation of ribosomes.
The remaining site of nucleolus is
filled in chromatin.
CYTOPLASM/
CYTOSOL
Granulated structures.
All the sub cellular organelles are
embedded.
Part of Gluconeogenesis.
Site for most of the metabolic
activities like HMP pathway, urea
cycle, glycolysis and synthesis of
purins and pyramidins.
TRANSPORT PROCESS ACROSS THE CELL MEMBRANES:
Biological membranes are semi-permeable membrane (allow only certain into the cell).
Two types of transport process-
1. Passive transport- It is of two types Simple diffusion and Facilitated diffusion.
2. Active transport- It is of two types primary active transport and secondary active transport ( co-
transport and Counter transport)
TRANSPORT PROCESS
PASSIVE TRANSPORT
Lipid soluble molecules can easily transport from intracellular to
extracellular.
Ions are being transported without utilization of
ATP/carrier/energy.
Ions move from higher concentration to lower concentration.
SIMPLE DIFFUSION
Ions move from higher concentration to lower concentration.
Lipophillic (lipid loving substances) can be transported.
FACILITATED DIFFUSION
ACTIVE TRANSPORT
PRIMARY ACTIVE
TRANSPORT
SECONDARY ACTIVE
TRANSPORT
CO-TRANSPORT
COUNTER TRANSPORT
ENERGY RICH COMPOUNDS:
Certain compounds are encountered in the biological system which on hydrolysis yield
energy.
Energy rich compounds is usually applied to substances which passes sufficient free energy to
liberate at least 7 cal/mole at pH 7.
All the high energy compounds when hydrolyzed liberate more energy than that of ATP. These
includes phosphoneol pyruvate, 1,3-bisphosphoglycerate, phosphocreatine etc.
Most of the high energy compounds contain phosphate group (exception acetyl co-a). Hence
they are called high energy phosphate compounds.
CLASSIFICATION OF HIGH ENERGY COMPOUNDS-
CLASS
BOND
EXAMPLE
Pyrophosphate
ATP, Pyrophosphate
Acid Phosphates
1,3-bisphosphoglycerate,
Carbonyl phosphate.
Enol Phosphates
Acetyl Phosphate Phosphoenol
pyruvate.
Thioesters
Acetyl Co-A, Acyl Co-A.
Guanido phosphates
(phosphogens)
Phosphocreatine,
Phosphoarginine.
The high energy compounds posses acid anhydride bonds (mostly phosphoanhydride bonds)
which are formed by condensation of two acidic groups or related compounds. These bonds are
called high energy bonds since the free energy is liberated when these bonds are hydrolysed.
Symbol ( ) to represent high energy bond.
ATP:
SYNTHESIS OF ATP- 2 ways:
1. OXIDATIVE PHOSPHORYLATION.
2. SUBSTRATE LEVEL PHOSPHORYLATION.
SYNTHESIS OF ATP
EXPLANATION
OXIDATIVE
PHOSPHORYLATION
Major source of ATP in all organisms.
Linked with mitochondria ETC.
Phosphocreatine or creatine phosphate stored in muscel of
brain as an energy rich compound.
SUBSTRATE LEVEL
PHOSPHORYLATION
Directly synthesized during substrate oxidation.
High energy compounds such as PEP, 1,3-Bisphosphate,
Glycerate, Succinyl C0-A transfer high energy phosphate to
ultimately produce ATP.
It is a high energy compound due to the presence of 2-phosphoanhydride
bonds in triphosphate unit.
It serves as the energy currency of the cell.
Hydrolysis of ATP releases large amount of energy. ATP+H20--------ADP + Pi (7.3 cal).
Energy liberated is utilized for various process like muscle contraction, active transport
etc.
It acts as donar of high energy phosphate to low energy compounds to make them
energy rich.
ADP can accept high energy phosphate from coumpounds possessing higher free
energy content to form ATP.
ATP-ADP cycle- fundamental basis of energy exchange reactions in living system. They
act as link between catabolism and anabolism in biological system.
In vertebrate phophoarginine replaces phosphocreatine.
CAMP: (Cyclic adenosine 3-5 monophosphate).
DEGRADATION:
CAMP undergoes rapid hydrolysis catalized by the enzyme phosphodiesterase to 5-AMP which is
inactive.
Effect of CAMP will be short lived if the hormone stimulating adenylate cyclase is removed.
Caffine and theophylline can inhibit phosphodiesterase enzyme and increases the intracellular
levels of CAMP.
It is a ubiquitous (found everywhere in our living system) nucleotide.
It is made up of adenine, ribose and phosphate which is linked by 3-5’ linkage.
It acts as 2
nd
messenger for majority of polypeptide hormone.
Membrane bound enzyme “adenylate cyclase” (present in or attached with the cell
membrane) converts ATP to CAMP.
Cyclic AMP is hydrolysed by “Phosphodiesterase” (breaks cyclic AMP to 5-AMP, makes
active form to inactive form) to 5-AMP.