http://www.ibscrewed.org/ A presentation for IB Biology students that covers everything you need to know for Transcription and Translation.

1. Transcription and Translation
www.ibscrewed.org

2. DNA vs. RNA
DNA RNA
Deoxyribose sugar (pentose) Ribose sugar (pentose)
Bases: A, T, G, C Bases: A, U, G, C
Double-strand helix Single-strand helix
Very long Relatively short

3. What is transcription?
Since our DNA molecules are too large to leave the
nucleus, a smaller mRNA molecule is formed.
Takes place in the nucleus – 5i to 3i direction

4. HL Stuff to know
Starting point is the “promoter region”
Nucleotides are attached by RNA polymerase
Covalent bonds between nucleotides
Moves along the antisense strand
Stops when it reaches the “terminator sequence”
Introns are removed through splicing and broken
down in the nucleus – makes mature mRNA

5. DNA helicase – RNA polymerase

6. Codons
Triplets of bases on the mRNA strand
Some are start codons and stop codons

7. Translation
Takes place in the cytoplasm – 5i to 3i
Ribosomes are the enzymes – small subunit and
large subunit

8. Activation of tRNA
The corresponding amino acid binds to the tRNA at
the 3i end
Uses tRNA-activating enzyme
The code is degenerate – one amino acid may bind
to different types of tRNA

9. Code:
A = Blue
U = Red
G = Yellow
C = Green

10. Initiation
First tRNA molecules binds to the start codon AUG

11. Elongation
More tRNA bind, polypeptide bonds form between amino
acids

12. Translocation
The tRNA has detached from its amino acid and is
released from the E (exit) site

13. Termination
Ribosome reaches stop codon (no matching tRNA), mRNA
is released and ribosome separates
Polypeptide folds into secondary, tertiary structure

14. Gene = Polypeptide???
Most of the time, yes
BUT! – some genes do not code for mRNA that
produces polypeptides
Some just control the expression of other genes
Does it matter where the ribosome is??
YES!
Free in the cytoplasm = protein used in the cell
Attached to ER = secreted outside the cell

15. Peptide bond