Unit: 1 - gene expression

Question 1

What is the definition of gene expression?

Answer 1

Gene Expression: The process by which the information in a gene is used to synthesize a functional gene product, typically a protein (or RNA in some cases).
Includes two main stages: transcription and translation.

Question 2

What are the stages of Gene Expression?

Answer 2

Transcription (Occurs in the nucleus in eukaryotes)
Definition: The process of copying a gene’s DNA sequence into a complementary RNA sequence.
Steps:
Initiation:
RNA polymerase binds to the promoter region of the gene.
In eukaryotes, transcription factors help RNA polymerase attach to the promoter.
Elongation:
RNA polymerase moves along the DNA template strand, synthesizing a complementary mRNA strand.
Uses base pairing rules: A pairs with U (instead of T), and C pairs with G.
Termination:
RNA polymerase stops transcription when it reaches a terminator sequence.
The newly synthesized pre-mRNA (in eukaryotes) is released.
Post-Transcriptional Modifications (in eukaryotes):
5’ Cap: A modified guanine nucleotide is added to the 5’ end for stability and ribosome recognition.
Poly-A Tail: A chain of adenine nucleotides is added to the 3’ end to protect mRNA from degradation.
Splicing: Introns (non-coding regions) are removed, and exons (coding regions) are joined together.

Translation (Occurs in the cytoplasm at ribosomes)
Definition: The process of converting the mRNA sequence into a polypeptide chain (protein).
Key Players:
mRNA: Contains the codons (3-base sequences) that code for amino acids.
tRNA: Transfers amino acids to the ribosome; has an anticodon that pairs with mRNA codons.
Ribosome: Site of translation; composed of a large and small subunit.
Steps:
Initiation:
The small ribosomal subunit binds to the mRNA at the start codon (AUG).
tRNA carrying methionine (anticodon UAC) binds to the start codon.
The large ribosomal subunit attaches, forming the translation complex.
Elongation:
tRNA brings the correct amino acids to the ribosome as it reads each mRNA codon.
Peptide bonds form between amino acids, creating a polypeptide chain.
The ribosome moves along the mRNA in the 5’ to 3’ direction.
Termination:
Translation ends when the ribosome encounters a stop codon (UAA, UAG, or UGA).
The polypeptide is released, and the translation complex disassembles.

Question 3

what is Gene Regulation?

Answer 3

Purpose: Ensures genes are expressed only when needed, conserving resources and allowing cell specialization.
Levels of Regulation:
Transcriptional Control:
Determines if a gene is transcribed.
Example: Operons in prokaryotes (e.g., lac operon for lactose metabolism).
Post-Transcriptional Control:
mRNA processing (splicing, capping, and tailing) and degradation.
Translational Control:
Regulates how efficiently mRNA is translated into protein.
Post-Translational Control:
Modifications to proteins after synthesis (e.g., folding, phosphorylation).
Epigenetic Regulation:
Changes to gene expression without altering the DNA sequence.
DNA Methylation: Adding methyl groups to DNA, silencing gene expression.
Histone Modification: Acetylation loosens chromatin to promote transcription; deacetylation tightens it to repress transcription.

Question 4

what are the differences between eukaryotic and prokaryotic gene expression?

Answer 4

prokaryotic:
location: Cytoplasm
mRNA processing: None(no introns or modifications)
Transcription and translation: occur simultaneously
Gene regulation: Operons(e.g lac operon)

Eukaryotic:
location: nucleus(Transcription) and cytoplasm(translation)
mRNA processing: introns removed, 5’ cap, and poly A-tail added
Transcription and translation: Separated(translation occurs after transcription)
Gene regulation: complex regulation(e.g. enhancers, silencers)

Question 5

What is a gene?

Answer 5

A segment of DNA that code for a protein or RNA

Question 6

What is a promoter?

Answer 6

A DNA sequence where RNA polymerase binds to start transcription

Question 7

What is a codon?

Answer 7

A three base sequence on mRNA that codes for an amino acid

Question 8

What is an anti codon?

Answer 8

A three base sequence on tRNA complementary to an mRNA codon

Question 9

What is an operon?

Answer 9

A cluster of genes in prokaryotes regulated together(e.g. lac operon)

Question 10

What is an epigenetics?

Answer 10

Study of changes in gene expression without changes to the DNA sequence

Question 11

What are some applications of gene expression?

Answer 11

1. biotechnology
2. medicine
3. evolution