Protein Synthesis

Question 1

What are the three stages of DNA transcription?

Answer 1

Initiation, elongation, and termination.

Question 2

What enzyme is responsible for transcribing DNA into RNA?

Answer 2

RNA polymerase.

Question 3

What is the function of the promoter sequence in transcription?

Answer 3

It is a DNA sequence that signals RNA polymerase where to begin transcription.

Question 4

What is the difference between the 3’-5’ and 5’-3’ DNA strands?

Answer 4

The 3’-5’ strand is the transcribed (template) strand, while the 5’-3’ strand is the non-transcribed (coding) strand.

Question 5

What is post-transcriptional modification?

Answer 5

The process where introns are removed, and exons are joined to form mature mRNA (splicing).

Question 6

Where does translation occur in the cell?

Answer 6

At the ribosomes.

Question 7

What are the three stages of translation?

Answer 7

Initiation, elongation, and termination.

Question 8

What is the function of tRNA in translation?

Answer 8

It carries amino acids to the ribosome and matches them to the codons on mRNA.

Question 9

What is the start codon, and what amino acid does it code for?

Answer 9

AUG, which codes for methionine.

Question 10

What are stop codons?

Answer 10

UAA, UAG, and UGA; they signal the end of translation.

Question 11

What organelle modifies and packages proteins for transport?

Answer 11

The Golgi apparatus.

Question 12

What is the role of the endoplasmic reticulum in protein synthesis?

Answer 12

It helps in protein folding and transport.

Question 13

How are proteins transported within the cell?

Answer 13

Via vesicles.

Question 14

What does it mean that the genetic code is universal?

Answer 14

Almost all organisms use the same codons to code for the same amino acids.

Question 15

How can mutations in DNA affect protein synthesis?

Answer 15

They can lead to changes in mRNA, which may alter the amino acid sequence of a protein.

Question 16

What is a frameshift mutation?

Answer 16

A mutation caused by insertions or deletions that shift the reading frame of the genetic code.

Question 17

What are the consequences of mutations in start or stop codons?

Answer 17

They can prevent translation from starting or stopping properly, leading to nonfunctional proteins.

Question 18

What are pulse-chase experiments used for?

Answer 18

To track the movement and processing of newly synthesized proteins in cells.

Question 20

What did the Nirenberg, Khorana, and Holley experiments demonstrate?

Answer 20

They helped decipher the genetic code and how codons specify amino acids.

Question 21

What can electrophoresis be used for in genetics?

Answer 21

To analyze DNA or protein sequences and identify mutations.

Question 22

How is DNA sequencing used in forensics?

Answer 22

To match DNA from crime scenes to individuals.

Question 23

What is transgenesis?

Answer 23

The introduction of foreign DNA into an organism to study gene function.

Question 24

How do inducible and repressible operons regulate gene expression?

Answer 24

Inducible operons (e.g., lac operon) activate gene expression in response to a molecule, while repressible operons (e.g., trp operon) suppress gene expression when a product is abundant.

Question 25

Why is the genetic code described as “universal” and “degenerate”?

Answer 25

• The same set of codons (combinations of nucleotides) codes for the same amino acids in nearly all living organisms, from bacteria to humans. • Degenerate means that multiple codons can code for the same amino acid. For example, there are several different codons that can all code for leucine, so even if there's a mutation in one of the codons, it may still code for the same amino acid, reducing the impact of some mutations.

Question 27

Classify these mutations based on their type and effect: 1.UAU —> UAA (to a stop codon) 2.GAA —> GAC (changes the a a) 3.GGU —> GGC ( no change in a a )

Answer 27

1. Type: point mutation Effect: nonsense mutation (introduces a premature stop codon) 2. Type: point mutation Effect Effect: missense mutation (amino acid changes from glutamic acid to aspartic acid) 3. Type: point mutation Effect: silent mutation (still codes for glycine - no change in protein)

Question 28

What does “non-overlapping” genetic code mean?

Answer 28

The genetic code is non-overlapping, meaning each codon is read as a separate set of three bases. If it were overlapping, one mutation could affect several codons, leading to many incorrect amino acids and a much higher chance of nonfunctional proteins.

Question 29

Explain how a *missense* mutation could be more or less harmful than a *nonsense* mutation depending on where it occurs.

Answer 29

A *missense* mutation changes one amino acid, which may or may not affect protein function. If the new amino acid is similar to the original or not in a critical region, the protein might still function. A *nonsense* mutation introduces a premature stop codon, often producing a shortened, nonfunctional protein. If it occurs early in the sequence, it is usually more harmful. Therefore, nonsense mutations are often more damaging, especially when they happen early in the gene.

Question 30

What are the roles of the *promoter* and *terminator* sequences in transcription?

Answer 30

The *promoter* is a region of DNA where RNA polymerase binds to initiate transcription. It marks the start of a gene. The *terminator* is a sequence that signals RNA polymerase to stop transcription. It ensures that only the correct portion of DNA is transcribed into mRNA, helping regulate gene expression and ensuring proper RNA processing.

Question 31

What would happen during translation if a tRNA molecule with an incorrect anticodon binds to a codon?

Answer 31

The incorrect tRNA would insert the wrong amino acid into the polypeptide chain. This changes the amino acid sequence, which may alter the protein's structure and function. If the change affects a critical region, such as an enzyme's active site, the protein may not h work correctly, potentially disrupting cellular processes.

Question 32

Why is it important that the genetic code is *non-overlapping*? What would happen if it were overlapping?

Answer 32

In a non-overlapping code, each codon is read as a separate group of three bases. This ensures that the genetic message is read correctly and consistently. If the code were overlapping, one mutation could affect multiple codons, leading to more widespread errors in the amino acid sequence and potentially nonfunctional proteins. Non-overlapping reading ensures fewer errors and greater stability in protein synthesis.

Question 33

Name two structural differences between DNA and RNA.

Answer 33

DNA is double-stranded and contains thymine; RNA is single-stranded and contains uracil.

Question 34

What sugar does RNA contain? What about DNA?

Answer 34

RNA contains ribose; DNA contains deoxyribose.

Question 35

What are the four nitrogenous bases in RNA?

Answer 35

Adenine, uracil, cytosine, guanine.

Question 36

What are the two main stages of protein synthesis, and where do they occur?

Answer 36

Transcription (in the nucleus) and translation (at ribosomes in the cytoplasm).

Question 37

What enzyme is responsible for building mRNA during transcription?

Answer 37

RNA polymerase

Question 38

What is the role of tRNA during translation?

Answer 38

It brings specific amino acids to the ribosome and matches them to mRNA codons using its anticodon.

Question 39

What is the function of the ribosome in protein synthesis?

Answer 39

It reads the mRNA and helps form peptide bonds between amino acids.

Question 40

What is a codon?

Answer 40

A sequence of three bases on mRNA that codes for one amino acid.

Question 41

What does it mean that the genetic code is "degenerate"?

Answer 41

Multiple codons can code for the same amino acid.

Question 42

What does it mean that the genetic code is "universal"?

Answer 42

The same codons code for the same amino acids in almost all organisms.

Question 43

What are the roles of the promoter and terminator sequences in transcription?

Answer 43

The promoter is where RNA polymerase binds to begin transcription; the terminator signals it to stop.

Question 44

What is the correct order of events in protein synthesis?

Answer 44

1) mRNA is transcribed, 2) Ribosome binds to mRNA, 3) tRNA brings amino acids, 4) Polypeptide is released.

Question 45

What is a point mutation?

Answer 45

A change in a single base pair in the DNA sequence

Question 46

Silent mutation

Answer 46

A mutation that does not change the amino acid produced

Question 47

Missense mutation

Answer 47

A mutation that changes one amino acid in the protein

Question 48

Nonsense mutation

Answer 48

A mutation that changes a codon to a stop codon, ending translation prematurely