As you come in
• Make two lists under the 2 headings:- ‘Features I got from my mum and
dad’- ‘Features I did not get from my mum
and dad’
Learning objectives• Recall the differences between
environmental and inherited effects• What is a gene?• How does a gene code for a polypeptide
Success criteriaComplete bracelet models to describe
translation.Take away knowledge of key terms.
What is a ‘gene’?What is a ‘locus’?
• Write on a post it note….Stick it on to the chromosome
I think a gene is a type of mythical creature with 3 heads…….
Bracelet sequencing• Decide whether you are a chimp or a
human:
CTATTTGTGGT TCTGAGTTCTTAAAACCCAGTG CTTCGAAGG
Making DNA• Order the original dna sequence
using colour code.• Make a complimentary strand of DNA
(remember DNA is a double helix)
A = blue T = redC = green G = black
Learning objectives• Be able to describe the genetic code• Explain and compare the structure of
RNA(t and m) and DNA• Explain the preocess of transcription
and splicing.
The triplet codeGiven that there are four bases in DNA, and these code for 20 amino acids, what is the basis for the genetic code?
If three bases = one amino acid, possible aminoacids = 64 (4×4×4)
The existence of a three-base (triplet) code was confirmed by experiments by Francis Crick and his colleagues in 1961. The triplet code is degenerate, which means that each amino acid is coded for by more than one triplet.
What is mRNA?When a polypeptide is required, the triplet code of its gene is converted into a molecule of messenger RNA (mRNA).
This process is called transcription and is the first stage of protein synthesis.
Like DNA, mRNA is a nucleic acid, but it differs in that:
it is single stranded, not double stranded
it contains ribose instead of deoxyribose
it contains uracil instead of thymine.
mRNA strand during
transcription
U A G
tRNAmolecule
Differences between DNA and RNA
• Bases• Structure• Pentose sugar• Where is it
found?• Quantity in cells• Stability?
Transcription and codonsDuring transcription, the mRNA is built up by complementary base pairing, using the DNA as a template. The DNA’s base triplets are converted into mRNA codons.
What are the codons in the mRNA transcribed from this sequence of DNA base triplets?
DNA
mRNA
T A C G C A G A T T A C A U G C G U C U A A U G
The genetic code is non-overlapping: each base is only part of one triplet/codon, and each triplet/codon codes just one amino acid.
OVERLAPPING
AACGTAAGCACGTTCGCACCCCAAACACAC
EACH CODON CODES FOR ONE AMINO ACID. However these may be the same amino acid.
What is tRNA?
nucleotides
amino acidattachment site
anticodon
In the cytoplasm, amino acids become attached to transfer RNA (tRNA) molecules. Each tRNA is specific for one amino acid.
Each tRNA molecule has a sequence of three bases called an anticodon. These are complementary to codons on the mRNA molecule.
3’ end
5’ end
hydrogen bond
What is the anticodon for the codon A U G
U A C
What is translation?Once a molecule of mRNA has been transcribed, it moves out of the nucleus via a nuclear pore.
In the cytoplasm, the mRNA combines with a ribosome – the cellular structure on which the polypeptide chain will be built in a process called translation.
How are the correct amino acids transported to the ribosome, and how are they linked together in the correct order?
mRNA strand
ribosome
Next step in the polypeptide process
• Unwind your double helix• You are going to write the mRNA
sequence to your original DNA strand on your strip of card.
AGCUGUCUAGUAB
C
Next is the tRNA• Write on your tRNA molecules the
anticodons which are complimentary to the codons on your mRNA sequence.
• Next, write down the Amino Acids which are attatched to the specific amino acids.
AMINO ACID LINKED TO tRNA ANTICODONS
Valine - CAU/ CACAspargine – UUGSerine – AGAGlutamate - CUCPhenylalanine – AAA/AAGLeucine - AAUArganine - GAAProline - GGU
What happens during translation?tRNA molecules attach to the ribosome, and their anticodons pair up with the appropriate codons on the mRNA.
The amino acids transported by the tRNA link together, and the tRNA molecules then return to the cytoplasm.
The ribosome moves along the mRNA, and amino acids continue to join together until all the codons have been translated and the polypeptide is complete.
Draw a chromosome
SIMILARITIES
DIFFERENCES
mRNAANDtRNA
CODONAND
ANTICODON
DNAANDRNA
Extension ‘ how do genes code for polypeptides?’
Answer this question using the following key words:
Gene complimentary transcribe Ribosome tRNA Amino acids peptide bonds DNA translate mRNA
Learning objectives• What is a gene?• How does a gene code for a
polypeptide
Success criteriaComplete bracelet models to describe
translation.Take away knowledge of key terms.