The document discusses the molecular basis of DNA and mutations. It explains that DNA is made up of a sequence of bases (A, T, G, C) that encode instructions for making proteins. Mutations are changes in the DNA sequence that can be caused by errors in DNA replication or exposure to mutagens. There are different types of mutations like substitutions, insertions, and deletions that can change protein sequences. Living cells have repair mechanisms but failure can lead to a higher mutation rate.

1. Presented To :Sir Khalid Hussain
Presented by: 09040606-028
The molecular basis and
mutations

2. The molecular basis and mutations
 DNA is made of a long
sequence of smaller units
strung together. There are
four basic types of unit:
A, T, G, and C. These
letters represents the type
of base each unit carries:
adenine, thymine, guanine,
and cytosine.

3.  The sequence of these bases encodes
instructions. Some parts of our DNA are control
centers for turning genes on and off, some parts
have no function, and some parts have a function
that we don't understand yet.
 Other parts of our DNA are genes that carry the
instructions for making proteins — which are
long chains of amino acids. These proteins help
build an organism.

5. Mutations
 Mutations are changes in the
DNA sequence of genes.
 Point mutations typically refer
to alterations of single base
pairs of DNA or of a small
number of adjacent base pairs.
 Mutations in DNA cause
substitutions in protein

6.  New mutations are categorized as induced or
spontaneous
 Induced mutations are defined as those that
arise after purposeful treatment with
mutagens, environmental agents that are
known to increase the rate of mutations
 Spontaneous mutations are those that arise in
the absence of known mutagen treatment. They
account for the "background rate" of mutation
and are presumably the ultimate source of
natural genetic variation that is seen in
populations

7. Mutation can be classified as:
a- Germline - affecting tissues that
produces eggs & sperm
( heritable meiotically between
generations)
b-Somatic mutations occur in non-
reproductive cells and won't be passed
onto offspring. For example, the golden
color on half of this Red Delicious
apple was caused by a somatic
mutation. Its seeds will not carry the
mutation.

8. Substitutions:
 A substitution is a mutation that exchanges
one base for another (i.e., a change in a
single "chemical letter" such as switching an
A to a G). Such a substitution could:

9. Substitutions
 1- Silent substitutions the mutation changes one
codon for an amino acid into another codon for that
same amino acid
2- Missense mutations the codon for one amino
acid is replaced by a codon for another amino acid
3- Nonsense mutations the codon for one amino
acid is replaced by a translation termination (stop)
codon

10.  Insertion:
Insertions are mutations in which
extra base pairs are inserted into a
new place in the DNA.
 Deletion:
Deletions are mutations in which a
section of DNA is lost, or deleted.

11. Effects of mutation
 Mutations happen for several reasons.
1. DNA fails to copy accurately.
2. External influences can create mutations.
Mutations can also be caused by exposure to
specific chemicals or radiation. These agents
cause the DNA to break down.

13. Biological Repair Mechanisms
 Living cells have evolved a series of
enzymatic systems that repair DNA damage
in a variety of ways.
 The low spontaneous mutation rate is
indicative of the efficiency of these repair
systems.
 Failure of these systems can lead to a
higher mutation rate.