Dr.Saidunnisa, M.D Professor and chairperson Biochemistry Relationship between cell Biology and Biochemistry

Learning Objectives At the end of the session the student shall be able to: 1. Enumerate the sub cellular organelles of the cell 2. Describe each organelle structure, function and disorder associated.

Cell Basic unit of biological activity.

Eukaryotic cell

Nucleus Is 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.

Mitochondria Mitochondria 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 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 Diseases Which 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 DNA Mitochondria contain DNA that can replicate. It is more susceptible for mutations than nuclear DNA. Mt DNA is maternally inherited.

Learning Check A 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?

Peroxisomes These 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 H 2 O 2 which is subsequently degraded in Peroxisomes to H 2 O and O 2 by catalase and peroxidase.

Catalase is the marker enzyme of Peroxisomes.

Peroxisomes function 1. Oxidation of VLCFA (containing more than 20 carbons) to shorter chain FA. 2. Conversion of cholesterol to bile acids.

Peroxisomal diseases 1. Zellweger syndrome: Peroxisomes synthesis is deficient. VLCFA are not oxidized they accumulate in tissues like brain, liver and kidney.

Endoplasmic Reticulum These 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 Complex The 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.

Lysosomes 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-Mannose-6- phosphate.

As they are actively involved in digestion of cellular substances- 1. Carbohydrates- α -Glucosidase 2. Proteins-Cathepsins 3. Lipids-Lipases 4. Nucleic acids-Ribo and deoxy ribo nucleases

Lysosomal disorders 1. Lysosomal storage disease is due to genetic defects in lysosomal enzymes. Example: Tay- Sachs and Pompes disease.

Apoptosis When the cell has fulfilled its biological functions cell death occurs this is called programmed cell death or apoptosis.