Ch. 15
Transcription & Translation
RNA types
1. Ribosomal RNA (rRNA): make
up ribosomes
2. Transfer
RNA (tRNA): transport amino acids to ribosomes
3. Messenger RNA (mRNA): copied
from DNA, conveys information from chromosomes to ribosomes
Transcription: production of mRNA
copy of the DNA gene.
Gene: Section of DNA within a chromosome
that codes for the synthesis of one protein. There are roughly 20-30,000 genes
on the 23 pairs of human chromosomes.
Only 1 side of DNA in a gene gets transcribed:
A. Sense Strand: Strand of DNA
in a gene which has the same nucleotide sequence as the m-RNA (except with
T instead of U).
B. Antisense Strand: Name of strand
of DNA that is transcribed to create m-RNA. It is the template used for making
m-RNA.
RNA polymerase: enzyme that initiates transcription by binding
to promoter (TAC code on DNA) at the 3' end of DNA
Promoter site: sequences in the
DNA strand which accept RNA polymerase and initiate transcription
Elongation: mRNA bonds with DNA
in small units, transcription bubble, adding bases Adenine to uracil &
Guanine to cytosine, etc.. in the 5' to 3' direction (on the new m-RNA).
Termination: stop signal disengages
RNA polymerase
Codon: sequence of 3 nucleotides
on m-RNA that codes for one amino acid. Each amino acid has one to several
different codons.
Much of DNA is non-coding base sequences, not genes
Intron: part of gene (DNA or mRNA)
that does not code for polypeptide. It must be removed before translation.
Exon: coding part of DNA (or mRNA).
The exon is translated during protein synthesis.
Translation: synthesis of protein
by ribosomes
Anticodon: the 3 nucleotide sequence
on t-RNA which the ribosome must fit against m-RNA to ensure that the correct
amino acid is placed in the growing protein during translation.
Initiation: Initiates translation.
rRNA polymerase of ribosome binds to mRNA strand.
1st tRNA is bonded to mRNA.
Elongation: Ribosome reads mRNA
chain in three nucleotide groups (codon) & inserts 2nd tRNA.
tRNA anti-codon (with amino acid) binds to mRNA codon
Translocation: 5' to 3' sequence continues building amino
acid polymers (protein), one codon at a time.
Termination: tRNA recognizes release
factors of nonsense codon. Newly completed polypeptide is released from ribosome
General information:
1. Universality of Nucleic Acids:
All organisms contain nucleic acids. It is a common thread of all life! It's
possible to transplant nucleic acids from one species to another as a result!
1. Degeneracy of genetic code: 64
codons possible for 20 amino acids (Ensures several possible codon combinations
for each amino acid which helps prevent mutations.) (See
Table 15.1)
2. Anticodon & codon both three nucleotides long
3. 45 types of tRNA
4. Much of DNA is base sequences, not genes
5. Intron: part of gene (DNA or
mRNA) that doesn't code for polypeptide
6. Exon: coding part of DNA (or
mRNA)
7. Splicing: as mRNA matures, non-coding
(introns) parts are removed (See Figs. 15.17 & 15.18)
8. nonsense (stop) codons are UAA, UAG, UGA
9. Start (promotor codon) signal is AUG
10. A gene is a DNA base sequence, a polypeptide is the protein
coded by the gene.
Long & Slichter