DNA Replication
& Protein Synthesis
DNA Replication
In the nucleus.
 During Interphase.
 Copies the cell’s genetic information
ready for mitosis.
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DNA Replication
Conservative, semi-conservative or
dispersive?
The Meselson-Stahl Experiment
Each strand of DNA acts as a template for
synthesising a new one.
Protein Synthesis

Objectives:

* state that a gene is a sequence of nucleotides as part of a
DNA molecule, which codes for a polypeptide;
**describe the way in which the nucleotide sequence codes for
the amino acid sequence in a polypeptide;
***explain that, as enzymes are proteins, their synthesis is
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controlled by DNA
1. The DNA double helix ‘unzips’ and the
hydrogen bonds between the bases break.
P
P
2. Free nucleotides in the nucleus are
activated by 2 extra phosphates.
4. DNA polymerase links the sugar
and phosphate groups of
neighbouring nucleotides together.
3. The bases of the active
nucleotides pair up with their
complementary base on the
DNA template.
Protein Synthesis
In the nucleus and cytoplasm.
 Creates peptide chains from the DNA
template.
 Divided into transcription & translation.

DNA  RNA amino acids
describe how the information on DNA is used to construct
polypeptides, including the role of messenger RNA, transfer
RNA and the ribosomes

http://wwwclass.unl.edu/biochem/gp2/m_biology/a
nimation/gene/gene_a1.html
Comparison of DNA, mRNA
and tRNA
Feature
Double/Single
Size
Shape
Sugar
Bases
Quantity in
cells
Stability
DNA
mRNA
tRNA
Comparison of DNA, mRNA
and tRNA
Feature
DNA
mRNA
tRNA
Double/Single
Double
Single
Single
Size
Largest
Variable
Smaller
Shape
Double helix
Single helix
Clover shape
Sugar
Deoxyribose
Ribose
Ribose
Bases
A, G, T, C
A, G, U, C
A, G, U, C
Quantity in cells
Constant
(gametes)
Varies
Varies
Stability
Very stable
Unstable
More stable than
mRNA, less than
DNA
Transcription – In the nucleus

RNA polymerase binds to promoter region of DNA
(usually before a single gene) from a chromosome.

Elongation - Free mRNA nucleotides base pair with
complementary bases on only one of the DNA
strands – the template strand.

Termination - The new strand of mRNA detaches
from the DNA template and leaves the nucleus via a
nuclear pore.
tRNA molecules have three unpaired bases – an
anticodon.
Free
tRNA
The
also has an amino acid binding site.
mRNA molecule binds to a ribosome via it’s small subunit.
The
first 3 exposed bases, or codon, are always AUG, and a
tRNA molecule with the complimentary anticodon, UAC,
hydrogen bonds to it.
Therefore
the first amino acid is methionine
Translation – In the cytoplasm

.

The enzyme peptidyl transferase forms peptide
bonds between the amino acids.
 The ribosome moves down the mRNA ‘reading’ each
codon in turn, and the earlier tRNA’s detach.
 Polypeptide chain grows until a ‘stop’ codon, UAA,
UAC or UGA prevents further translation.
Summary
Compare the relationship between DNA
and nucleotide with amino acids and
protein
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RNA polymerase binds to the promoter region
This initiates transcription
RNA polymerase uncoils the DNA
Only one strand is used, the template strand
Free nucleoside triphosphates bond to their complementary
bases on the template strand
Adenine binds to uracil instead of thymine
As the nucleoside triphosphates bind they become nucleotides
and release energy by losing two phosphate groups
The mRNA is built in a 5'→3' direction
RNA polymerase forms covalent bonds between the nucleotides
and keeps moving along the DNA until it reaches the terminator
The terminator signals the RNA polymerase to stop transcription
RNA polymerase is released and mRNA separates from the
DNA
The DNA rewinds
The Triplet Code
http://www.ibguides.com/bi
ology/notes/transcription-hl