INFORMATION TRANSFER
Overview
Intro
DNA Replication
Protein Synthesis
Antibiotics and how they interrupt DNA Rep. and Protein synthesis
Mutations and genetic disorders
Introduction
What is a gene?
Gene: the basic physical unit of heredity/a linear sequence of nucleotides along a segment of DNA
Why is it important?
It provides the coded instructions for synthesis of RNA. So that it can be translated into protein,
leading to the expression of hereditary character.
DNA Replication intro:
Before cells divide, they have to double the organelles and DNA. DNA Replication takes
place.
DNA is double stranded; if the information is lost on one strand there is another strand to
replace the information
DNA can change its nucleotide sequence by acquired mutations – Evolution (Some
mutations are harmful)
DNA REPLICATION
What is semi-conservative replication?
Semi-conservative DNA replication involves splitting open the parent cell’s DNA duplex and exposing
both strands. Now these strands act as a template, so that the sequence can be 'read' and a
daughter strand synthesised that is complementary to each parent strand. This will produce two
DNA duplexes which have one parent strand and one daughter strand.
Why is semi conservative replication important?
The semi-conservative mechanism minimises errors in DNA replication because the template gives
DNA polymerase something accurate to copy from. This is very important because cells want to
minimise errors in replication when dividing, so that mutations (such as incorrect bases, deletions,
insertions) are not brought into the genome.
Steps of DNA replication
Initiator proteins and DNA helicase binds to DNA
Helicase unwinds the two strands
A replication bubble is formed.
Single-stranded DNA-binding proteins (SSB) stabilize the single-stranded template DNA
during the process
, Replication proceeds in both directions
Primase synthesizes a short RNA primer of 10-12 nucleotides
DNA polymerase adds nucleotides (5’ to 3’) on both strands
New bases pair with their complementary bases
The RNA primer is removed and replaced with DNA by another polymerase and the gap is
sealed with DNA ligase
Two double helixes form that are copies of original DNA
What is the role of primer in DNA replication?
To initiate this reaction, DNA polymerases require a primer (with a free 3′-hydroxyl group) already
base-paired to the template. They cannot start from scratch by adding nucleotides to a free single-
stranded DNA template.
The replication fork
The replication fork is half of the replication bubble. There are 2 anti-parallel strands in DNA, and
DNA replication occurs in the 5’ to 3’ direction ONLY.
This results in a leading strand (3’ to 5’) and a lagging strand (5’ to 3’).
In the 5’ strand (lagging strand) the replication occurs in a discontinuous manner resulting in the
formation of Okazaki fragments. These are joined together by DNA Ligase .
RNA primer portions are removed and replaced by DNA by the action of a different DNA polymerase.
Protein Synthesis
Intro
Protein synthesis takes place on ribosomes
The information in the DNA which is located in the nucleus in eukaryotes has to be carried to
the ribosomes in the cytoplasm
Overview
Intro
DNA Replication
Protein Synthesis
Antibiotics and how they interrupt DNA Rep. and Protein synthesis
Mutations and genetic disorders
Introduction
What is a gene?
Gene: the basic physical unit of heredity/a linear sequence of nucleotides along a segment of DNA
Why is it important?
It provides the coded instructions for synthesis of RNA. So that it can be translated into protein,
leading to the expression of hereditary character.
DNA Replication intro:
Before cells divide, they have to double the organelles and DNA. DNA Replication takes
place.
DNA is double stranded; if the information is lost on one strand there is another strand to
replace the information
DNA can change its nucleotide sequence by acquired mutations – Evolution (Some
mutations are harmful)
DNA REPLICATION
What is semi-conservative replication?
Semi-conservative DNA replication involves splitting open the parent cell’s DNA duplex and exposing
both strands. Now these strands act as a template, so that the sequence can be 'read' and a
daughter strand synthesised that is complementary to each parent strand. This will produce two
DNA duplexes which have one parent strand and one daughter strand.
Why is semi conservative replication important?
The semi-conservative mechanism minimises errors in DNA replication because the template gives
DNA polymerase something accurate to copy from. This is very important because cells want to
minimise errors in replication when dividing, so that mutations (such as incorrect bases, deletions,
insertions) are not brought into the genome.
Steps of DNA replication
Initiator proteins and DNA helicase binds to DNA
Helicase unwinds the two strands
A replication bubble is formed.
Single-stranded DNA-binding proteins (SSB) stabilize the single-stranded template DNA
during the process
, Replication proceeds in both directions
Primase synthesizes a short RNA primer of 10-12 nucleotides
DNA polymerase adds nucleotides (5’ to 3’) on both strands
New bases pair with their complementary bases
The RNA primer is removed and replaced with DNA by another polymerase and the gap is
sealed with DNA ligase
Two double helixes form that are copies of original DNA
What is the role of primer in DNA replication?
To initiate this reaction, DNA polymerases require a primer (with a free 3′-hydroxyl group) already
base-paired to the template. They cannot start from scratch by adding nucleotides to a free single-
stranded DNA template.
The replication fork
The replication fork is half of the replication bubble. There are 2 anti-parallel strands in DNA, and
DNA replication occurs in the 5’ to 3’ direction ONLY.
This results in a leading strand (3’ to 5’) and a lagging strand (5’ to 3’).
In the 5’ strand (lagging strand) the replication occurs in a discontinuous manner resulting in the
formation of Okazaki fragments. These are joined together by DNA Ligase .
RNA primer portions are removed and replaced by DNA by the action of a different DNA polymerase.
Protein Synthesis
Intro
Protein synthesis takes place on ribosomes
The information in the DNA which is located in the nucleus in eukaryotes has to be carried to
the ribosomes in the cytoplasm
