Biology Protein Synthesis Overview

Study Notes

Protein Synthesis Overview

Protein synthesis occurs in two stages: transcription and translation.
Transcription happens in the nucleus.
Translation happens in the cytoplasm.

Transcription

mRNA is created from a DNA template.
RNA polymerase synthesizes mRNA in the 5' to 3' direction.
The template strand of DNA is used to create mRNA.
The coding strand of DNA matches the mRNA sequence (except uracil replaces thymine).
A promoter region on the DNA signals where RNA polymerase binds to start transcription.
mRNA carries genetic information from DNA to the ribosome.

Post-Transcriptional Modifications

mRNA undergoes changes to become mature:
- Capping: A 5' cap is added for protection and recognition by ribosomes.
- Tailing: A poly-A tail is added to the 3' end for stability.
- Splicing: Introns (non-coding regions) are removed, and exons (coding regions) are joined together.

Translation

Converting mRNA into a protein occurs in the cytoplasm.
Ribosomes, made of rRNA and proteins, are the sites of translation.
tRNA carries amino acids to the ribosome. Each tRNA has an anticodon complementary to an mRNA codon.
The start codon (AUG) initiates translation and codes for methionine.
Stop codons (UAA, UAG, UGA) signal the end of translation.
The ribosome has three sites (A, P, and E) for tRNA binding.
- The A site receives incoming tRNA.
- The P site holds the growing polypeptide chain.
- The E site is the exit site for tRNA.
mRNA provides the codons that specify the amino acid sequence.

Gene Expression Regulation

Gene expression is controlled to ensure the correct proteins are produced at the right time.
Types of controls:
- Transcriptional control: Regulates transcription initiation (e.g., repressors/activators).
- Post-transcriptional control: Involves splicing, capping, and tailing.
- Translational control: Regulates mRNA stability and ribosome activity.
- Post-translational control: Modifications to proteins after translation.

Lac Operon (Prokaryotes)

Controls lactose metabolism in E. coli.
Inducible operon: Active in the presence of lactose.
Lactose acts as an inducer, deactivating the repressor.
The repressor blocks transcription in the absence of lactose.

Trp Operon (Prokaryotes)

Controls tryptophan synthesis.
Repressible operon: Active by default, but turned off by tryptophan.

Mutations

Changes in the DNA sequence.
Types of mutations:
- Point mutations: Affect a single nucleotide.
  - Missense: Changes one amino acid.
  - Nonsense: Creates a stop codon.
  - Silent: No change to the amino acid sequence.
- Frameshift mutations: Insertion or deletion that alters the reading frame.
- Large-scale mutations:
  - Translocations: Chromosome segments exchange places.
  - Inversions: A chromosome segment reverses direction.
  - Deletions: Large sections of DNA lost.
  - Amplifications: Repeated sections of DNA.
Causes of mutations:
- Spontaneous: Errors during DNA replication.
- Induced: Caused by environmental factors (UV, chemicals, viruses).
Effects of mutations:
- Positive: Increased genetic diversity; beneficial traits aiding evolution.
- Negative: Harmful disorders/diseases like cancer.

Genetic Manipulation

Tools and techniques used to modify genes.
Key terms:
- Plasmids: Circular bacterial DNA used as vectors in genetic engineering.
- Restriction enzymes: Cut DNA at specific recognition sites.
- Recombinant DNA: DNA formed from combining different sources.
- Gel electrophoresis: Technique to separate DNA fragments of different lengths.

Description

Explore the process of protein synthesis, which includes transcription and translation. Learn about how mRNA is synthesized in the nucleus and the subsequent translation in the cytoplasm, as well as the modifications mRNA undergoes to become mature. This quiz will test your understanding of these critical biological processes.