Download Protein Synthesis In the nucleus - DNA is split by DNA helicase

SICM Tuition
Biology AS
Protein Synthesis
In the nucleus
DNA is split by DNA helicase
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as it is split, free nucleotides bind to the exposed bases of the NON-CODING
STRAND (this is because it is complementary – it is the opposite of what will be
on the tRNA – which is the actual amino acid)
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this process is helped by RNA polymerase
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the nucleotides join together to form mRNA (messenger RNA)
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the DNA closes back together
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the mRNA formed is then spliced:
o in this process, the introns (which are NON-CODING) are removed
o the exons (which are CODING) are kept
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SICM Tuition
Biology AS
In the cytoplasm
the spliced mRNA then moves out of the nucleus via a nuclear pore
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the mRNA goes to a ribosome
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the first triplet code to be read is AUG. This codes for the start codon
(methionine)
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the codes on the mRNA are called codons
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the ribosome can hold 2 triplet codes together…
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the mRNA enters the ribosome and as it does so, tRNA (transfer RNA) comes
and joins complementary bases to it. The complementary triplet bases on the tRNA
are called anti-codons.
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a tRNA molecule is made up of three bases at one end and an amino acid at the
other end
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many different tRNA molecules are present in the cytoplasm for this to occur
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this continues and as it does, the amino acids line up (2 at a time – as each
ribosome can hold 2 triple codes) and bond together by peptide bonds catalysed
by the enzyme peptidyl transferase.
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This continues until a stop codon is reached. The stop codons do not code for any
amino acid, but stop the translation.
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many amino acids make up a protein
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the mRNA that moves along can simply be re-used again and again
Translation animation
Highly recommended….very nice way to put it all together
http://www.maxanim.com/genetics/Protein%20Synthesis/Protein%20Synthesis.htm
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SICM Tuition
Biology AS
A
T
G
C
T
A
base pairs
A
T
G
C
T
A
sugar phosphate backbone
A
A
T
C
G
C
G
The enzyme DNA helicase breaks the
hydrogen bonds between the cases causing
the strands to separate (to unzip) from one
end.
One original molecule of DNA
A
T
T
A
G
T
C
T
A
G
C
T
A
T
C
G
A
A
A
T
C
T
G
G
C
C
G
G
T
C
A
G
C
Complementary bases join with hydrogen
bonds and free nucleotides link up to for a
new strand
The exposed bases attract the
complementary bases of free DNA
nucleotides. (e.g. C will only attract G)
A
T
G
C
T
A
original (old) DNA strand
A
T
G
C
T
A
A
T
C
G
new strand
Two exact copies of the
original DNA molecule have
been made
A
T
C
G
The sequence of the bases is
kept exactly the same due to
specific base pairing
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SICM Tuition
Biology AS
The Human Genome Project
Ethical issues
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A part of a DNA molecule which codes for a single polypeptide is called a
gene.
In humans, it is estimated that there are about 140 000 genes
The total set of genes is called the genome
The genome represents the genetic code for a particular organism
The human genome project was a project to find out the FULL base
sequence of the human genome
There are about 3 billion bases in the human genome. The aim is to
identify each human gene
This was completed in 2003
gene testing:
o can improve lives but has problems such as abortion issues
possibility of cloning
SYLLABUS CHECKLIST
Unit 2.1.2 – Nucleic Acids
Candidates should be able to:
(a)
state that deoxyribonucleic acid (DNA) is a polynucleotide, usually double
stranded, made up of nucleotides containing the bases adenine (A), thymine (T),
cytosine (C) and guanine (G);
(b)
state that ribonucleic acid (RNA) is a polynucleotide, usually single stranded,
made up of nucleotides containing the bases adenine (A), uracil (U), cytosine
(C) and guanine (G);
(c)
describe, with the aid of diagrams, how hydrogen bonding between
complementary base pairs (A to T, G to C) on two antiparallel DNA
polynucleotides leads to the formation of a DNA molecule, and how the twisting
of DNA produces its ‘double-helix’ shape (HSW1);
(d)
outline, with the aid of diagrams, how DNA replicates semi-conservatively, with
reference to the role of DNA polymerase;
(e)
state that a gene is a sequence of DNA nucleotides that codes for a polypeptide
(HSW3);
(f)
outline the roles of DNA and RNA in living organisms (the concept of protein
synthesis must be considered in outline only).
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