Dr.Saidunnisa, M.DDr.Saidunnisa, M.D

Professor and chairperson Biochemistry

Relationship between cell Biology and Biochemistry

Learning ObjectivesLearning Objectives At the end of the session the

student shall be able to:1. Enumerate the sub cellular

organelles of the cell2. Describe each organelle

structure, function and disorder associated.

CellCellBasic unit of biological activity.

Eukaryotic cellEukaryotic cell

NucleusNucleusIs the largest sub cellular

organelle of an eukaryotic cell.

It is surrounded by a double membrane nuclear envelope.

The outer membrane is continuous with the membranes of rough endoplasmic reticulum.

The inner membrane has numerous pores called nuclear pores..

Nucleus contains DNA, the chemical basis of genetic information, these are associated with proteins called histones to form chromatin and are further organized into chromosomes.

DNA is transcribed into RNA, which is modified and edited into mRNA, this travels through the nuclear pores into the cytoplasm,.

where it is translated into the primary sequence of a protein on ribosome's.

MitochondriaMitochondriaMitochondria are rod-shaped

structures ranging from 2 to 8 micrometers in length.

They are found throughout the cytoplasm and may account for up to 20% of the cell's volume.

Mitochondria function during aerobic respiration to produce ATP through oxidative Phosphorylation.

These are power houses of the cell.

Structure of mitochondria Structure of mitochondria Mitochondria are

surrounded by two membranes.

The outer membrane forms the exterior of the organelle

while the inner membrane is arranged in a series of folds called Cristae to provide an enormous surface area for chemical reactions.

The space between the

inner and outer mitochondrial membranes is called the intermembrane space.

while the compartment enclosed by the inner mitochondrial membrane is called the matrix.

Inner mitochondrial membrane contains enzymes of electron transport chain.

Matrix contains enzymes of citric acid cycle, Fatty acid (beta) oxidation, urea and heme synthesis.

Mitochondrial DiseasesMitochondrial DiseasesWhich will effect the tissues rich

in ETC like skeletal, neuronal and renal tissues.

These disorders are (MELAS). Mitochondrial encephalopathy, Lactic acidosis, and Stroke-like episodes

Mitochondrial DNAMitochondrial DNAMitochondria

contain DNA that can replicate .

It is more susceptible for mutations than nuclear DNA.

Mt DNA is maternally inherited.

Learning CheckLearning CheckA patient had a sudden heart

attack caused by inadequate blood flow through the vessels of the heart. As a consequence there was an inadequate supply of oxygen to generate ATP in his cardiomyocytes. Which compartment of the cardiomyocyte most directly involved in ATP generation?

PeroxisomesPeroxisomesThese are cytoplasmic organelles.They contain peroxidases and catalase

enzymes.Present in leukocytes and platelets in

high concentration.These are involved in oxidation

reactions, which produce a toxic chemical H2O2 which is subsequently degraded in Peroxisomes to H2O and O2 by catalase and peroxidase.

CatalaseCatalase is the is the markermarker enzyme of Peroxisomes.enzyme of Peroxisomes.

Peroxisomes functionPeroxisomes function

1. Oxidation of VLCFA (containing more than 20 carbons) to shorter chain FA.

2. Conversion of cholesterol to bile acids.

Peroxisomal diseasesPeroxisomal diseases

1. Zellweger syndrome: Peroxisomes synthesis is

deficient. VLCFA are not oxidized they accumulate in tissues like brain, liver and kidney.

Endoplasmic ReticulumEndoplasmic ReticulumThese are thread like structures

extend from the nuclear pores to the plasma membrane.

A large portion of the ER is studded with ribosome's to give a granular appearance which is referred as RER.

Ribosome's are the factories of Protein biosynthesis.

Smooth ER does not contain ribosome's.

It is involved in the:1. synthesis of lipids (TAG,

Phospholipids, Sterols).2. Metabolism of drugs

(Cytochrome P450).3. Metabolism of toxic chemicals

(ethanol).

Golgi ComplexGolgi ComplexThe newly synthesized proteins

from RER are handed over to golgi complex.

Which catalyze the addition of carbohydrates, lipids or sulfate moieties to the proteins.

These chemical modifications are necessary for the transport of proteins across the plasma membrane.

LysosomesLysosomes These are spherical vesicles. The pH of Lysosomes is lower

(5) than cytosol (7). They are bag of enzymes

regarded as the digestive tract of the cell.

Lysosomal enzymes are categorized as Hydrolases.

Marker for lysosomes-Marker for lysosomes-Mannose-6-phosphate.Mannose-6-phosphate.

As they are actively involved in digestion of cellular substances-

1.Carbohydrates- α-Glucosidase2.Proteins-Cathepsins3.Lipids-Lipases4.Nucleic acids-Ribo and deoxy ribo

nucleases

Lysosomal disordersLysosomal disorders1. Lysosomal storage disease is due to

genetic defects in lysosomal enzymes. Example: Tay-Sachs and Pompes disease.

ApoptosisApoptosisWhen the cell has fulfilled its

biological functions cell death occurs this is called programmed cell death or apoptosis.