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
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
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