(Study Material) Zoology Study Material For AIPMT and State PMT Examination (Cell Structure and Function)
Study Material : Zoology Study Material For AIPMT and State PMT Examination (Cell Structure and Function )
Cell Organelles
Cell Membrane
Function - It regulates what enters and leaves the cell (also called
selective permeability). It also gives the cell shape and protection.
Structure - Made up of two layers of phospholipids with proteins embedded
randomly in the layers. Lipid soluble substances, like alcohol, easily pass
across the membrane by dissolving in it. Lipid insoluble substances cannot pass,
and water passes through protein lined pores.
Rough Endoplasmic Reticulum
Function -Primarily concerned with protein synthesis and transport. Most highly
developed in protein exporting cells (eg. liver and pancreatic cells)
Structure - It is a series of interconnected membranes which spread throughout
the cytoplasm forming channels of flattened sacs, with ribosomes attached to
them. The channels formed by the membranes transport the proteins made by the
ribosomes.
Smooth Endoplasmic Reticulum
Function - synthesizes and transports lipids and steroids. Some kinds of smooth
E.R. accepts, modifies, and transports proteins from the rough E.R. and still
other kinds break down energy rich glycogen and fats.
Structure - The smooth E.R. is free of ribosomes so has a smooth appearance. The
channels formed are similar to those formed by the rough E.R. but are tubular
and are concerned with making and transporting lipids and steroids.
Golgi apparatus (body)
Function - Proteins exported from the rough and smooth E.R. are modified and
enclosed in secretory or lysosomal vesicles and transported out of the cell.
Structure - The golgi appear as flattened stacks of membranes. The proteins
enter these membranes are modified, concentrated and packaged into small
spherical membrane bound structures called vesicles.
Lysosomes
Function - digests and disposes of foreign particles, malfunctioning structures,
and worn out organelles.
Structure - The contents of the lysosome are contained within vesicles. The
lysosome contains 40 or so different enzymes that are capable of breaking down
virtually every large biological molecule, including DNA, RNA, proteins, and
certain lipids.
Mitochondria
Function - The chemical reactions which produce energy and the storage of that
energy as ATP occur in this organelle. Glucose and Oxygen are used to produce
ATP, carbon dioxide and water. Collectively these reactions are called aerobic
respiration.
Structure -The structure is characterized by a double membrane which creates two
areas within the organelle. The area between the membranes houses the enzymes of
the Kreb's cycle and is called the matrix. The other area, on the surface of the
membranes, contains the enzymes of the electron transport system and is called
the cristae. Be able to recognize the cristae and matrix in the diagram of the
mitochondria below
Nucleus
Function - acts to control the metabolic activities of the cell. Is the
central control centre which monitors internal and external conditions and turns
on or off different genetic programs.
Structure - is surrounded by a membrane which is similar in structure to the
plasma or cell membrane. Nuclear pores or holes occur at intervals along the
membrane. These holes provide a way for the nucleus to communicate with the
cytoplasm. Substances pass in and out of the nucleus through these openings.
Nucleolus
Function - Rich in RNA and is the site of the synthesis of ribosomes
Structure - consists of densely packed chromosomes, protein and precursor RNA
strands from which the subunits of ribosomes are formed.
Vacuole
Function - In plants it can act as a storage area for ions, metabolic
products such as sugars and amino acids, and toxic compounds. Its main function
however is to increase cell size and surface area so that the absorption of ions
is enhanced.
Structure - Fluid pressure builds up in the vacuole causing the cell to become
elongated and extended increasing surface area and cell size. It is bounded by a
cell membrane.
Chromosome
Function - Carries the genetic code which determines characteristics of an
organism.
Structure - made up of genes which are in turn made up of DNA. The chemical
components and the order of the chemical components determine the specific
characteristics.
Cell wall
Function - allows plant cells to withstand high internal pressure without
bursting.
Structure - made of cellulose (provides the rigidity) cemented together with
lignin.
Vesicles
Function - Contain products that have been packaged/modified by the golgi. (eg.
proteins like enzymes, plasma proteins, peptide hormones etc.) It has the same
structure as a vacuole only it is smaller in size. Structure W in the first
diagram and structure Z in the second, show vesicles.
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