This document discusses the subcellular organelles found within cells. It describes the nucleus as the most prominent organelle, containing DNA which governs cell functions. Other organelles discussed include the endoplasmic reticulum, Golgi body, lysosomes, and mitochondria, with each having distinct metabolic functions like protein synthesis, degradation, and ATP generation. Mitochondria are specifically described as the powerhouses of the cell, containing enzymes for electron transport and energy production.

1. Section 1
Chemical Basis
of Life

3. 1. Subcellular Organelles
Cells contain various organised structures, collectively
called as cell organelles. When the cell membrane is
disrupted, the organised particles inside the cell are
homogenised. They could then be separated by applying
differential centrifugal forces.
Fig. 1.1. A typical cell

4. JAYPEE GOLD STANDARD MINI ATLAS SERIES BIOCHEMISTRY4
Nucleus is the most prominent organelle of the cell. All
cells contain nucleus, except mature RBCs in circulation.
In some cells, nucleus occupies most of the available space,
e.g.smalllymphocytesandspermatozoa.Nucleuscontains
the DNA, the chemical basis of genes which governs all
the functions of the cell. It is further organised into
chromosomes. DNA replication and RNA synthesis
(transcription) are taking place inside the nucleus.
Fig. 1.2. Nucleus

5. SUBCELLULAR ORGANELLES 5
Table 1.1. Metabolic functions of subcellular organelles
Nucleus : DNA replication, transcription
Endoplasmic : Biosynthesis of proteins,
reticulum glycoproteins, lipoproteins, drug
metabolism, ethanol oxidation,
synthesis of cholesterol (partial).
Golgi body : Maturation of synthesised proteins.
Lysosome : Degradation of proteins, carbo-
hydrates, lipids and nucleotides.
Mitochondria : Electron transport chain, ATP
generation, TCA cycle, beta
oxidation of fatty acids, ketone
body production, urea synthesis
(part), heme synthesis (part).
Cytosol : Protein synthesis, glycolysis,
glycogen metabolism, HMP shunt
pathway, transaminations, fatty
acid synthesis, cholesterol
synthesis (part), heme synthesis
(part), urea synthesis (part),
pyrimidine synthesis (part), purine
synthesis.

6. JAYPEE GOLD STANDARD MINI ATLAS SERIES BIOCHEMISTRY6
Fig. 1.3. Mitochondria
Mitochondria are spherical, oval or rod-like bodies,
about 0.5 to 1 μm in diameter and up to 7 μm in length.
Erythrocytes do not contain mitochondria. The tail of
spermatozoa is fully packed with mitochondria.
Mitochondria are the powerhouse of the cell. The inner
membrane contains the enzymes of electron transport
chain. The fluid matrix contains the enzymes of citric acid
cycle, urea cycle and heme synthesis.

7. SUBCELLULAR ORGANELLES 7
The structure of the biomembranes was described as a
fluid mosaic model (Singer and Nicolson, 1972). The
phospholipids are arranged in bilayers with the polar head
groups oriented towards the extracellular side and the
cytoplasmicsidewithahydrophobiccore.Thelipidbilayer
shows free lateral movement of its components, hence the
membrane is said to be fluid in nature.
Fig. 1.4. The fluid mosaic model of membrane

8. JAYPEE GOLD STANDARD MINI ATLAS SERIES BIOCHEMISTRY8
Fig. 1.5. Transport mechanisms

9. SUBCELLULAR ORGANELLES 9
Fig. 1.6. The sodium-potassium pump. It brings sodium ions out
of the cells and potassium ions into the cells. (A) Sodium ions
within the cell fit into channel. (B) The channel changes shape,
pumping the sodium ions. Potassium ions outside the cell move
into receptor sites. (C) Sodium ions are released, potassium ions
are pumped into the cell. (D) Potassium ions are released inside
the cell.

10. JAYPEE GOLD STANDARD MINI ATLAS SERIES BIOCHEMISTRY10
Table 1.3. Types of transport mechanisms
Carrier Against Energy Examples
gradient required
Simple diffusion No No Nil Water
Facilitated Yes No Nil Glucose to
diffusion RBCs
Primary active Yes Yes Directly Sodium
pump
Secondary Yes Yes Indirect Glucose to
active intestine
Ion channels Yes No No Sodium
channel
Table 1.2. Comparison of cell with a factory
Plasma : Fence with gates; gates open
membrane when message is received
Nucleus : Manager’s office
Endo.reticulum : Conveyer belt of production units
Golgi apparatus : Packing units
Lysosomes : Incinerators
Vesicles : Lorries carrying finished products
Mitochondria : Power generating units