1. DNA
as the
genetic code

2. a GENE is
A sequence of bases on a DNA molecule which codes for a sequence of amino acids in a polypeptide chain

3. A sequence of 3 DNA bases in a gene which code for a single amino acid
a BASE TRIPLET is
A sequence of 3 DNA bases in a gene which code for a single amino acid
4 Bases = A C G T
Examples AGC
CTA

4. and reads each codon independently of the next
THE GENETIC CODE IS
NON-OVERLAPPING
A code that starts
at one end of the gene
and reads each codon independently of the next
AUG
AGC
ACC
GAG
amino acid 1
amino acid 2
amino acid 3
amino acid 4

5. More than one base triplet can code for a particular amino acid
THE GENETIC CODE IS
DEGENERATE
More than one base triplet
can code for a particular amino acid

6. HOWEVER only 20 different amino acids have to be coded for.
If the order of the bases is important there are 64 different ways of arranging four bases in a triplet code.
HOWEVER only 20 different amino acids have to be coded for.

7. Some codes are used as initiation codons to indicate the beginning of a gene
Some are stop codons and indicate where a gene terminates
Others are used as alternative codons for some amino acids

9. TRANSCRIPTION translation PROTEIN SYNTHESIS This involves 2 processes
Copying a gene in the nucleus to make mRNA
translation
Using the mRNA to make proteins in the cytoplasm

10. tRNA
IN NUCLEUS
IN CYTOPLASM
Ribosome
mRNA
ENERGY (ATP)
transcription
translation
DNA
POLYPEPTIDE

11. DNA cannot move into the cytoplasm where polypeptides are produced.
TRANSCRIPTION
DNA cannot move into the cytoplasm where polypeptides are produced.
This reduces the possibility of damage to the DNA.

12. The process is controlled by the enzyme RNA polymerase.
The DNA code is transcribed (copied) into a single stranded messenger RNA (mRNA) molecule in the nucleus.
The process is controlled by the enzyme RNA polymerase.

13. This is called the coding or sense strand.
Only one of the DNA strands of the double helix carries the genetic code.
This is called the coding or sense strand.
This sense strand acts as a template for mRNA production.

14. DNA helicase separates the 2 strands by causing hydrogen bonds to break between the complementary base pairs in the gene and the DNA to unwind.

15. RNA polymerase attaches to the initiation code of the gene and moves along the template adding free RNA nucleotides to the exposed DNA nucleotides

16. RNA nucleotides in the nucleoplasm attach to the exposed DNA bases.
Free complementary
RNA nucleotides in the nucleoplasm attach to the exposed DNA bases.
adenine
on the RNA
thymine
on the DNA
pairs with
uracil
on the RNA
adenine
on the DNA
whilst
pairs with
guanine always pairs with cytosine

17. RNA polymerase joins the sugar-phosphate backbone of the mRNA by condensation reactions.
The completed mRNA molecule passes through the nuclear pores in the nuclear membrane into the cytoplasm.
There are only 2 copies of each gene in the nucleus, but transcription allows many copies of mRNA to be available for translation and protein synthesis.

18. During transcription the whole gene is copied into mRNA
During transcription the whole gene is copied into mRNA. However genes contain long sequences of non-coding DNA called introns.
These are not required to make the protein therefore before the mRNA is used, these sequences are removed.

19. Part of DNA / gene to be copied
INTRON
(noncoding)
EXON
DNA template
double stranded
transcription
mRNA
after
Transcription
single stranded
modification
Modified mRNA
used by ribosome
to make protein

21. structure of mRNA p107 Froggy
single stranded
U replaces T
short
Ribose replace deoxyribose

22. tutorial 12.1 Transcription
animations
animation3
animation4
tutorial 12.1 Transcription
transgenic plant animation

23. AS GURU VIDEO

24. interactive transcription

25. draw structure of tRNA p109 Froggy
transfer RNA (tRNA)
Carries amino acids to the ribosomes during translation
tRNA is single stranded
Folded back in itself to form a clover shape, held by hydrogen bonds
Specific amino acids are attached to one end
A 3 base anticodon at the other end is complementary to a specific mRNA codon
draw structure of tRNA p109 Froggy

26. translation animation

27. read building a protein p110
draw diagram 1.4 p110
complete worksheet translation
Put the sentences in the correct order and then either rewrite or cut and paste
complete questions 1-10 p

28. reverse transcriptase
This is an enzyme which copies RNA into DNA

29. summary
Transcription involves unpairing of bases in one region of the DNA helix (the gene being read), followed by the synthesis of a strand of mRNA.
This carries a triplet code sequence complementary to the template strand of DNA (i.e. DNA acts as a template)
mRNA acts as a messenger to carry information to the ribosome in the cytoplasm.

30. Translation involves decoding/reading the triplet message on mRNA.
Each codon, 3 bases, has a natural complementary sequence of 3 bases, called the anticodon.
This set of 3 bases is attached to a specific tRNA molecule that carries and transfers a specific amino acid.
The specific amino acid is determined by the sequence of the triplet code and anticodon.

31. The complementary triplets on mRNA and tRNA pair together in ribosomal sites (peptidyl & aminoacyl).
Ribosomes are situated in the cytoplasm, hence the need for mRNA & tRNA.
When 2 amino acids sit side by side, at the two sites on the ribosome, a condensation reaction occurs and a peptide bond will form between them.

32. One gene
one polypeptide
theory