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http://www.ibscrewed.org/ A presentation for IB Biology students that covers everything you need to know for Transcription and Translation.
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DNA vs. RNA
DNA RNADeoxyribose 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
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
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
DNA helicase – RNA polymerase
Codons Triplets of bases on the mRNA strand Some are start codons and stop codons
Translation Takes place in the cytoplasm – 5i to 3i
Ribosomes are the enzymes – small subunit and large subunit
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
Code:
A = BlueU = RedG = YellowC = Green
Initiation First tRNA molecules binds to the start codon
AUG
Elongation More tRNA bind, polypeptide bonds form between
amino acids
Translocation The tRNA has detached from its amino acid
and is released from the E (exit) site
Termination Ribosome reaches stop codon (no matching tRNA),
mRNA is released and ribosome separates Polypeptide folds into secondary, tertiary structure
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
Peptide bond