Gene Expression

Question 1

What is gene expression?

Answer 1

The process by which DNA is used to synthesize a functional product (e.g., a protein).

Question 2

What is the central dogma of molecular biology?

Answer 2

DNA → RNA → Protein (transcription & translation).

Question 3

What is the difference between genotype and phenotype?

Answer 3

Genotype = inherited genetic information. Phenotype = observable traits influenced by genotype and environment.

Question 4

What are the three key stages of gene expression?

Answer 4

1. Transcription (DNA → RNA), 2. RNA Processing, 3. Translation (RNA → Protein).

Question 5

What is transcription?

Answer 5

The process of synthesizing RNA from a DNA template.

Question 6

What are transcription factors?

Answer 6

Proteins that bind to the promoter region to help initiate transcription.

Question 7

What is the promoter region?

Answer 7

A DNA sequence where RNA polymerase and transcription factors bind to start transcription.

Question 8

What are the template and coding strands?

Answer 8

Template strand = the DNA strand used to synthesize RNA. Coding strand = the DNA strand that has the same sequence as the RNA (except T → U).

Question 9

What happens during transcription initiation?

Answer 9

1. TATA box (in promoter) is recognized. 2. Transcription factors bind to the TATA box. 3. RNA Polymerase II binds, forming the transcription initiation complex. 4. Transcription starts.

Question 10

How does RNA polymerase move along DNA?

Answer 10

RNA polymerase moves 3’ to 5’ along the template strand, synthesizing RNA 5’ to 3’.

Question 11

What happens during transcription elongation?

Answer 11

RNA polymerase adds RNA nucleotides to the 3’ OH of the growing RNA strand, forming phosphodiester bonds.

Question 12

What happens during transcription termination?

Answer 12

1. The polyadenylation signal (AAUAAA) is transcribed. 2. Nuclear enzymes release pre-mRNA. 3. RNA polymerase II dissociates from DNA.

Question 13

What is pre-mRNA processing?

Answer 13

Modifications that turn pre-mRNA into mature mRNA before it leaves the nucleus.

Question 14

What are the three main steps of pre-mRNA processing?

Answer 14

1. Capping (5’ cap addition), 2. Tailing (Poly-A tail addition), 3. Splicing (removal of introns).

Question 15

What is capping?

Answer 15

A modified guanine nucleotide is added to the 5’ end of pre-mRNA.

Question 16

What are the functions of the 5’ cap?

Answer 16

1. Protects mRNA, 2. Increases stability, 3. Aids translation, 4. Helps transport through nuclear pores.

Question 17

What is tailing (Poly-A tail addition)?

Answer 17

50–250 adenine (A) nucleotides are added to the 3’ end of the pre-mRNA.

Question 18

What are the functions of the Poly-A tail?

Answer 18

1. Prevents degradation, 2. Helps nuclear export, 3. Aids in translation initiation.

Question 19

What is splicing?

Answer 19

Introns (non-coding regions) are removed, and exons (coding regions) are joined together to form mature mRNA.

Question 20

Why is splicing necessary?

Answer 20

Removes non-coding sequences so only protein-coding information is used during translation.

Question 21

Where does splicing occur?

Answer 21

In the spliceosome, inside the nucleus.

Question 22

What is the function of the spliceosome?

Answer 22

Removes introns and joins exons together using RNA-protein complexes.

Question 23

What happens if splice sites mutate?

Answer 23

It can lead to incorrect splicing, producing faulty or non-functional proteins.

Question 24

What is alternative splicing?

Answer 24

Different combinations of exons are used to create multiple proteins from a single gene.

Question 25

What is translation?

Answer 25

The process of converting mRNA into a protein by ribosomes in the cytoplasm.

Question 26

What are the key components of translation?

Answer 26

mRNA (template), tRNA (transfers amino acids), Ribosomes (protein synthesis site).

Question 27

What is the role of tRNA?

Answer 27

Carries amino acids and has an anticodon that binds to mRNA codons.

Question 28

What are the three steps of translation?

Answer 28

1. Initiation, 2. Elongation, 3. Termination.

Question 29

What happens during translation initiation?

Answer 29

1. Small ribosomal subunit binds to the 5’ cap of mRNA. 2. Initiator tRNA (carrying Met) binds to the AUG start codon. 3. Large ribosomal subunit attaches, forming the translation initiation complex.

Question 30

What happens during translation elongation?

Answer 30

1. Codon recognition – tRNA binds to the codon in the A site. 2. Peptide bond formation – The growing polypeptide chain moves from the P site to the A site. 3. Translocation – tRNA moves from A → P → E site, then exits.

Question 31

What happens during translation termination?

Answer 31

1. The ribosome reaches a stop codon. 2. A release factor binds instead of tRNA. 3. The polypeptide is released and the ribosomal subunits dissociate.

Question 32

What is the ribosome’s structure?

Answer 32

- Small subunit: Binds mRNA. - Large subunit: Has A site (acceptor site), P site (polypeptide site), E site (exit site) for tRNA.

Question 33

What is the Wobble Hypothesis?

Answer 33

There are 64 codons but only ~40 tRNAs because one tRNA can pair with multiple codons due to flexible base-pairing at the third codon position.

Question 34

Why is gene expression regulated?

Answer 34

To ensure proteins are made at the right time, in the right place, and in the right amount for spatial and temporal control.

Question 35

How is gene expression regulated?

Answer 35

1. Transcription factors assemble correctly. 2. DNA must be accessible for transcription. 3. mRNA modifications (splicing, polyadenylation). 4. mRNA stability affects how long translation occurs. 5. Regulatory proteins can prevent translation.

Question 36

What are housekeeping proteins?

Answer 36

Proteins that are constantly produced because they are always needed (e.g., tubulin).

Question 37

What is cell signaling’s role in gene expression?

Answer 37

Receptor activation → signal transduction → transcription activation → protein synthesis.

Question 38

What is post-translational modification?

Answer 38

Modifications to proteins after translation to make them functional.

Question 39

What are some types of post-translational modifications?

Answer 39

1. Phosphorylation (adds phosphate), 2. Methylation (adds methyl group), 3. Acetylation (adds acetyl group), 4. Carboxylation (adds carboxyl group), 5. Glycosylation (adds sugars), 6. Cleavage (cuts protein to activate it), 7. Ubiquitination (tags protein for degradation).

Question 40

Where do post-translational modifications occur?

Answer 40

In the Golgi apparatus or cytosol.

Question 41

Why are post-translational modifications important?

Answer 41

They regulate protein function, activity, stability, and location.