Biology Transcription and Translation

Study Notes

Transcription and Translation

Replication, Transcription, and Translation occur in eukaryotic cells.
- Replication takes place in the nucleus.
- Transcription takes place in the nucleus.
- Translation takes place in the cytoplasm.
DNA and RNA have distinct structures.
- DNA contains deoxyribose sugar.
- RNA contains ribose sugar.
- DNA bases are A, C, G, and T.
- RNA bases are A, C, G, and U.
- DNA is double-stranded.
- RNA is single-stranded.
RNA Polymerase is the enzyme responsible for synthesizing RNA.
A Transcription Complex assembles at the start of a gene, unwinding the DNA.
RNA Polymerase uses one strand of DNA as a template to build a complementary strand of RNA.
The RNA strand detaches from the DNA as it's transcribed, and the DNA zips back together.
tRNA delivers amino acids to the ribosome.
rRNA forms part of the ribosome structure.
mRNA carries the genetic code from DNA to the ribosome.
The large subunit of a ribosome binds to mRNA and holds tRNA molecules.
Each tRNA molecule has an anticodon that binds to a complementary codon on mRNA and an amino acid attached to the other end.
Translation occurs in three main steps:
- The ribosome moves along the mRNA strand, exposing a new codon.
- The ribosome forms a peptide bond between the amino acids, breaking the bond between the first amino acid and its tRNA.
- A complementary tRNA with an amino acid binds to the exposed codon.
Translation converts an mRNA message into a polypeptide.
- A codon is a sequence of three nucleotides that code for a specific amino acid.
- A reading frame defines the order in which nucleotides are read.
- Codons like AGG, GCA, and GUU are examples of three-nucleotide sequences.
- An anticodon on a tRNA molecule is complementary to an mRNA codon.
- A stop codon signals the termination of translation.

Mutations

A mutation is a change in an organism's DNA.
DNA Polymerase cannot catch and correct every replication error.
A mutagen is an environmental agent that can alter DNA.
UV light damages DNA by causing thymine nucleotides to bond with each other instead of adenine.
A frameshift mutation occurs when a nucleotide is deleted from DNA.

Examples

Amino Acid Sequence: Given the DNA sequence TAC TAT ACC GGT ACT, the resulting amino acid sequence would be Methionine-Isoleucine-Tryptophan-Proline-STOP.
Point Mutations: Point mutations may not always cause problems for the organism because:
- Multiple codons can code for the same amino acid.
- Silent mutations can change a codon without altering the amino acid it codes for.
- Mutations in non-coding regions or non-critical protein segments may not affect function.