Gene Structure And Expression

Question 1

What is the function of genes?

Answer 1

Genes influence traits by encoding proteins that perform biochemical, cellular, and organismal functions.

Question 2

What is the Central Dogma of molecular biology?

Answer 2

DNA → RNA → Protein

Question 3

What is transcription?

Answer 3

DNA is transcribed into RNA by RNA polymerase.

Question 4

What is translation?

Answer 4

RNA is translated into protein using ribosomes.

Question 5

What are non-coding RNAs?

Answer 5

Not all genes code for proteins (e.g., rRNA, tRNA); these RNAs have specialized functions.

Question 6

What components are included in gene structure?

Answer 6

Promoters, exons, and introns (in eukaryotes)

Question 7

What is the orientation of genes?

Answer 7

5’ → 3’

Question 8

What is a key difference in gene structure between prokaryotes and eukaryotes?

Answer 8

Prokaryotes lack introns.

Question 9

What do prokaryotes use for transcription termination?

Answer 9

Simpler termination sequences.

Question 10

What processes are required for RNA processing in eukaryotes?

Answer 10

Splicing, capping, polyadenylation.

Question 11

What do eukaryotes use for RNA polymerase binding?

Answer 11

Transcription factors.

Question 12

What are codons?

Answer 12

Triplets of nucleotides that encode amino acids.

Question 13

What is the start codon?

Answer 13

AUG (Methionine).

Question 14

What are the stop codons?

Answer 14

UAA, UAG, UGA.

Question 15

What is meant by redundancy in the genetic code?

Answer 15

Multiple codons encode the same amino acid due to ‘wobble pairing.’

Question 16

What are the four types of mutations?

Answer 16

• Silent
• Missense
• Nonsense
• Frameshift

Each type of mutation can affect protein function in different ways.

Question 17

What characterizes a silent mutation?

Answer 17

No change in protein.

Silent mutations do not affect the amino acid sequence of the protein.

Question 18

What is a missense mutation?

Answer 18

Amino acid substitution (e.g., sickle cell disease).

Missense mutations can lead to altered protein function.

Question 19

What happens in a nonsense mutation?

Answer 19

Premature stop codon.

Nonsense mutations can result in truncated proteins.

Question 20

Define frameshift mutation.

Answer 20

Alteration of the reading frame.

Frameshift mutations can significantly change the resulting protein.

Question 21

What are the potential impacts of mutations?

Answer 21

Can have evolutionary impacts or cause diseases.

Mutations can influence genetic diversity and disease susceptibility.

Question 22

What is the first step of transcription in eukaryotes?

Answer 22

Initiation: Transcription factors recruit RNA polymerase to the promoter.

This step is crucial for starting the transcription process.

Question 23

Describe the elongation phase of transcription.

Answer 23

RNA polymerase synthesizes RNA in 5’ → 3’.

This phase involves the addition of RNA nucleotides complementary to the DNA template.

Question 24

What occurs during the termination phase of transcription?

Answer 24

Cleavage occurs after the 3’ UTR.

This step marks the end of RNA synthesis.

Question 25

What is the purpose of 5' capping in RNA processing?

Answer 25

Stabilizes RNA; recognized by ribosomes. ## Footnote Capping is essential for mRNA stability and translation initiation.

Question 26

What is the function of the Poly(A) tail in RNA processing?

Answer 26

Protects RNA from degradation. ## Footnote The Poly(A) tail enhances mRNA stability and export from the nucleus.

Question 27

What is the role of splicing in RNA processing?

Answer 27

Removes introns; allows alternative splicing to create diverse proteins. ## Footnote Alternative splicing can lead to the production of multiple protein variants from a single gene.

Question 28

What is the first stage of translation?

Answer 28

Initiation: Ribosome assembles on mRNA at start codon ## Footnote The start codon is typically AUG, which codes for methionine.

Question 29

What occurs during the elongation stage of translation?

Answer 29

Amino acids added sequentially, reading the mRNA from 5' to 3' ## Footnote This process involves tRNA bringing amino acids to the ribosome.

Question 30

What triggers the termination stage of translation?

Answer 30

Stop codon prompts release of the ribosome ## Footnote Common stop codons include UAA, UAG, and UGA.

Question 31

What is the function of the A site on the ribosome?

Answer 31

Accepts new tRNA ## Footnote The A site is crucial for adding new amino acids during protein synthesis.

Question 32

What is the role of the P site on the ribosome?

Answer 32

Forms peptide bonds ## Footnote This site holds the tRNA carrying the growing polypeptide chain.

Question 33

What happens at the E site on the ribosome?

Answer 33

Releases empty tRNA ## Footnote The E site is where tRNA exits the ribosome after transferring its amino acid.

Question 34

What are polysomes?

Answer 34

Multiple ribosomes translating a single mRNA ## Footnote This allows for efficient and rapid protein synthesis.

Question 35

What are post-translational modifications?

Answer 35

Folding (chaperones), phosphorylation, glycosylation, lipidation ## Footnote These modifications can affect protein activity and stability.

Question 36

What is the main purpose of protein sorting?

Answer 36

Directs proteins to specific cellular locations ## Footnote This process is essential for maintaining cellular organization and function.

Question 37

What are sorting signals in proteins?

Answer 37

Specific sequences or structural features that act as 'postal codes' for protein targeting ## Footnote Sorting signals guide proteins to their correct destinations within the cell.

Question 38

What are signal peptides?

Answer 38

Short amino acid sequences at the N-terminus that direct proteins to the endoplasmic reticulum (ER) ## Footnote Signal peptides are essential for the initial targeting of proteins during synthesis.

Question 39

Define Nuclear Localization Signals (NLS).

Answer 39

Short sequences that direct proteins to the nucleus ## Footnote NLS are critical for the transport of proteins into the nucleus.

Question 40

What are transit peptides?

Answer 40

Target proteins to organelles like mitochondria or chloroplasts ## Footnote Transit peptides facilitate the import of proteins into specific organelles.

Question 41

Where are proteins destined for secretion or membrane synthesized?

Answer 41

In the rough endoplasmic reticulum (ER) ## Footnote The rough ER is studded with ribosomes, which synthesize these proteins.

Question 42

How are other proteins synthesized?

Answer 42

In the cytosol and sorted post-translationally ## Footnote This means that these proteins are synthesized first and then directed to their destinations.

Question 43

What is the role of a signal recognition particle (SRP)?

Answer 43

Binds the signal peptide on a nascent polypeptide and guides the ribosome to the SRP receptor on the ER membrane ## Footnote SRP plays a crucial role in initiating protein translocation into the ER.

Question 44

What occurs during translation into the ER?

Answer 44

The growing polypeptide chain is fed into the ER lumen ## Footnote This process allows for proper folding and modification of the protein.

Question 45

What happens to the signal peptide inside the ER?

Answer 45

It is removed by signal peptidase ## Footnote This step is essential for the maturation of the protein.

Question 46

What modifications occur inside the ER?

Answer 46

Folding and initial modifications such as glycosylation ## Footnote These modifications are important for protein functionality and stability.

Question 47

What is the role of the Golgi apparatus in protein sorting?

Answer 47

Proteins are further modified and sorted for final destinations like the plasma membrane or lysosomes ## Footnote The Golgi apparatus is a key site for protein processing and distribution.

Question 48

What directs proteins to specific organelles?

Answer 48

Transit peptides ## Footnote Transit peptides are short sequences that signal the destination of proteins within the cell.

Question 49

What role do chaperones play in protein sorting?

Answer 49

Assist in translocation across organelle membranes ## Footnote Chaperones help proteins fold properly and assist in their transport into organelles.

Question 50

What is the function of nuclear localization signals?

Answer 50

Allow proteins to pass through nuclear pores ## Footnote Nuclear localization signals are specific sequences that facilitate the import of proteins into the nucleus.

Question 51

Is full unfolding of the protein required for passage through nuclear pores?

Answer 51

No ## Footnote Proteins can pass through nuclear pores without fully unfolding.

Question 52

What tag is used to send proteins to lysosomes?

Answer 52

Mannose-6-phosphate ## Footnote This tag is added in the Golgi apparatus and directs proteins to lysosomes for degradation.

Question 53

What is phosphorylation in the context of protein sorting?

Answer 53

Activates or deactivates sorting signals ## Footnote Phosphorylation involves adding a phosphate group, which can change a protein's activity or its interactions.

Question 54

What role does glycosylation play in protein sorting?

Answer 54

Helps in sorting within the ER and Golgi ## Footnote Glycosylation is the addition of sugar molecules to proteins, which aids in their proper localization.

Question 55

What is lipidation's function in protein sorting?

Answer 55

Anchors proteins to membranes ## Footnote Lipidation involves the addition of lipid groups to proteins, facilitating their attachment to cell membranes.

Question 56

Why is protein sorting important for cells?

Answer 56

Maintains cellular compartmentalization ## Footnote Proper sorting ensures that enzymes and proteins are located where they can function effectively.

Question 57

What can errors in protein sorting lead to?

Answer 57

Diseases such as cystic fibrosis or lysosomal storage disorders ## Footnote Mis-sorted proteins can disrupt cellular functions and lead to various health conditions.