Biological Basis of Life
Basic Unit of life
• Cell
Biological Basis for Heredity
Somatic and Sex cells
Nucleus and Cytoplasm
• Cell organelles
– mitochondria, lysosomes, endoplasmic
reticulum, ribosomes
• Nucleus
– Chromosomes
» (chroma = colored; soma = bodies)
Chromosomes
• Number is specific to a species
Humans : 46 or 23 pairs
Roundworm: 2
Indian fern: 1260
• Two arms joined by a centromere
In Unwound state called chromatin.
Condensed into rod like structures
Chromosomes and Genetics
• Chromosome pairs are called homologous
chromosomes.
Homologous chromosomes carry genetic
information influencing the same traits.
Homologous chromosomes are not genetically
identical.
• Karyotype – photograph of chromosomes
chromosomal abnormalities
Types of Chromosomes
• Autosomes - governs all physical characteristics
except sex determination.
• Sex chromosomes - X and Y chromosome.
Mammal females have two X chromosomes.
Mammal males have one X and one Y
chromosome.
Biological Basis of Life
Deoxyribonucleic Acid
• DNA
provides the genetic code for the biological
structures
set of instructions for determining the make up
of biological organisms
• two polynucleotide chains
Nucleotide - sugar, phosphate and a base
Bases - Adenine, Guanine, Cytosine and
Thymine
Deoxyribonucleic acid
• Sugar and Phosphate form the backbone
and bases stick out like rungs of the ladder.
• Two chains are wound around in the form
of a spiral helix
• James D. Watson, Francis Crick, Maurice
Wilkins - 1953
• Nobel Prize 1962
• Replication – process of DNA duplication
Universal Genetic Code
• The DNA code of all life on earth is
composed of the same molecules and
carries on similar functions.
• The universality of the genetic code implies
a common ancestry for all life on the planet.
• Organisms differ according to the
arrangement of the DNA.
A Human Chromosome
Biological Basis of Life
Genes
• Section of DNA that codes for part of a
protein.
• Sequence of three bases is a codon.
• A codon is a code for an amino acid.
• A protein is a chain of amino acids.
• Exons: section of gene that code for protein
• Introns: do not contribute information for
protein synthesis
Ribonucleic Acid
•
•
•
•
•
assist in protein synthesis
m-RNA, t-RNA, r-RNA
Ribose sugar
Thymine replaced by Uracil
m-RNA and T-RNA single stranded
Protein Synthesis
• Transcription
DNA unzips
free floating RNA nucleotides attach to DNA
bases on the active strand
m-RNA formed leaves the nucleus
• Translation
ribosome moves along the m-RNA and decodes
t-RNA transports the appropriate amino acids
Biological Basis of Life
Mitosis
Mitosis
• Mitosis is cell division in somatic cells.
• Mitosis occurs during growth and
repair/replacement of tissues.
• The result of mitosis is two identical
daughter cells that are genetically identical
to the original cell.
Meiosis
• Gamete producing cells divide by Meiosis.
• It produces four daughter cells (since the
cell divides twice) with half the number of
chromosomes and they are not genetically
identical
• Meiosis increases genetic variation at a
faster rate than mutation.
Meiosis
Biological Basis of Life
Problems With Meiosis
• Nondisjunction
occurs when chromosomes don’t separate during
meiosis resulting in
trisomy (Down’s Edward’s, Patau’s syndrome)
Monosomy (Turner’s syndrome)
• Structural Abnormalities
Deletion, Addition, Inversion, Translocation
• Errors in meiosis may lead to spontaneous
abortion or miscarriage.