Biological Science 101 – General Biology
Lecture Five: From Gene to Protein
Ch. 17, Pgs. 325-348
Gene -> Proteins (Gene Expression)
- Biochemical traits.
- Phenotype traits.
- Polypeptides (proteins and some are enzymes).
DNA is transcribed to RNA
Ribonucleic acid -> Ribose sugar with Uracil base (not Thymine).
From DNA to RNA (Transcription)
Transcription = Producing RNA
Promoter (T-A-T-A region):
- Transcription factors binds to this area.
- RNA polymerase also binds here.
- DNA unwinds, nucleotides are added on the 5’ -> 3’ direction.
- Process is 40 nucleotides per second.
- Complementary strand is produced. Polyadenylation Releases Polymerase Pre-mRNA Strand
site (AAUAAA) -> Signal -> Detaches -> Released
- Take place in the nucleus.
Pre-mRNA -> mRNA.
1) Adds 5’ cap region. (5’ Cap region protects mRNA
from enzymatic degradation), which signals ribosomes
2) Add Poly A-Trail (AAAA). Inhibits mRNA degradation
and facilitates mRNA out of nucleus. RNA Slicing:
- Deletes the introns, joins up the exons (expressed) to produce mRNA, which is
used in translation.
Process of Translation: Occurs in the cytoplasm.
- Produces amino acids and joining them together to form a polypeptide (protein).
The Triplet Code:
On mRNA, the nucleotides are arranges in triplets (triplet code, a.k.a. codons).
UGC -> Codon (Tyrosine)
AGC -> Codon (Serine)
Dictionary of genetic code:
- Universal code (in all living organisms)
- 3-4 codons may produce the same amino acid.
- AUG = Start Codon.
- UAA, UAG, UGA = 3 Stop Codons Ribosomes = Small sub-unit and Large sub-unit:
- Contains ribosomal RNA.
- Most abundant type of RNA in cell.
Small sub-unit binds to the 5’ cap region.
Transfer RNA (tRNA) = Anti-codon at one end, which is
complementary to codon.
- It carries an amino acid specified by codon usage.
- First codon must be UAG (Start) -> Met.
- Large sub-unit binds to complex (energy is required GTP)
- It reads codons each time a new tRNA arrives, new amino
acid is added to pre