Transcription and Translation (unit 17)

Question 1

What do genes specify via transcription and translation?

Answer 1

Proteins

Genes dictate the synthesis of proteins, which are the links between genotype and phenotype.

Question 2

What is gene expression?

Answer 2

The process by which DNA directs protein synthesis, including transcription and translation.

Question 3

Who first suggested that genes dictate phenotypes through enzymes?

Answer 3

Archibald Garrod in 1902.

Question 4

What hypothesis did Beadle and Tatum’s experiments support?

Answer 4

The one gene–one enzyme hypothesis.

Question 5

What is the revised hypothesis regarding gene function?

Answer 5

One gene–one protein.

Question 6

What does the central dogma describe?

Answer 6

The flow of genetic information: DNA → RNA → protein.

Question 7

What is transcription?

Answer 7

The synthesis of RNA using information in DNA.

Question 8

What is the role of ribosomes in translation?

Answer 8

They are the sites of translation.

Question 9

What is a codon?

Answer 9

A triplet of nucleotides that corresponds to an amino acid.

Question 10

How many nucleotides correspond to an amino acid?

Answer 10

Three.

Question 11

How is the genetic code characterized?

Answer 11

Redundant but not ambiguous.

Question 12

What is the promoter in transcription?

Answer 12

The DNA sequence where RNA polymerase attaches.

Question 13

What are the three stages of transcription?

Answer 13

Initiation, elongation, termination.

Question 14

What is a transcription initiation complex?

Answer 14

The completed assembly of transcription factors and RNA polymerase II bound to a promoter.

Question 15

What modifications are made to pre-mRNA during RNA processing?

Answer 15

5′ cap and poly-A tail are added.

Question 16

What are introns?

Answer 16

Noncoding segments removed during RNA splicing.

Question 17

What is alternative RNA splicing?

Answer 17

The process where a single gene can encode more than one polypeptide.

Question 18

What is tRNA’s role in translation?

Answer 18

Transfers amino acids to the growing polypeptide chain.

Question 19

What is required for accurate translation?

Answer 19

Correct match between tRNA and amino acid, and tRNA anticodon and mRNA codon.

Question 20

What are the three binding sites in a ribosome?

Answer 20

• P site
• A site
• E site

Question 21

What occurs during the elongation stage of translation?

Answer 21

Amino acids are added one by one to the C-terminus of the growing chain.

Question 22

What signals the termination of translation?

Answer 22

A stop codon in the mRNA.

Question 23

What is a signal peptide?

Answer 23

A sequence of about 20 amino acids that directs polypeptides to specific locations.

Question 24

What are the two types of ribosomes in cells?

Answer 24

• Free ribosomes
• Bound ribosomes

Question 25

What is the function of the 5′ cap on mRNA?

Answer 25

Facilitates export of mRNA to the cytoplasm and helps ribosomes attach.

Question 26

What is the function of spliceosomes?

Answer 26

To remove introns during RNA splicing.

Question 27

What is wobble in the context of tRNA?

Answer 27

Flexible pairing at the third base of a codon allowing some tRNAs to bind to more than one codon.

Question 28

What is the primary structure of a protein determined by?

Answer 28

The gene encoding it.

Question 29

What do free ribosomes mostly synthesize?

Answer 29

Proteins that function in the cytosol ## Footnote Free ribosomes are not attached to any membrane and produce proteins used within the cell.

Question 30

What do bound ribosomes make?

Answer 30

Proteins of the endomembrane system and proteins that are secreted from the cell ## Footnote Bound ribosomes are attached to the endoplasmic reticulum.

Question 31

Can ribosomes switch between free and bound states?

Answer 31

Yes, ribosomes are identical and can switch from free to bound.

Question 32

Where does polypeptide synthesis always begin?

Answer 32

In the cytosol.

Question 33

What signals the ribosome to attach to the ER?

Answer 33

A signal peptide.

Question 34

What is a signal peptide?

Answer 34

A sequence of about 20 amino acids at or near the leading end of the polypeptide.

Question 35

What binds to the signal peptide?

Answer 35

A signal-recognition particle (SRP).

Question 36

What does the SRP do?

Answer 36

Escorts the ribosome to a receptor protein built into the ER membrane.

Question 37

What happens to the signal peptide after it is recognized?

Answer 37

It is removed by an enzyme.

Question 38

What is a polyribosome (or polysome)?

Answer 38

Multiple ribosomes translating a single mRNA simultaneously.

Question 39

What advantage do polyribosomes provide?

Answer 39

Enable a cell to make many copies of a polypeptide very quickly.

Question 40

How does a bacterial cell streamline protein production?

Answer 40

By coupling transcription and translation.

Question 41

What separates transcription and translation in eukaryotes?

Answer 41

The nuclear envelope.

Question 42

What occurs to RNA before it leaves the nucleus?

Answer 42

RNA undergoes processing.

Question 43

What are mutations?

Answer 43

Changes in the genetic information of a cell.

Question 44

What are point mutations?

Answer 44

Changes in just one nucleotide pair of a gene.

Question 45

What can a change of a single nucleotide in a DNA template strand lead to?

Answer 45

The production of an abnormal protein.

Question 46

What is referred to as a genetic disorder?

Answer 46

A mutation that has an adverse effect on the phenotype of the organism.

Question 47

What are the two general categories of small-scale mutations?

Answer 47

* Single nucleotide-pair substitutions * Nucleotide-pair insertions or deletions

Question 48

What is a nucleotide-pair substitution?

Answer 48

Replaces one nucleotide and its partner with another pair of nucleotides.

Question 49

What are silent mutations?

Answer 49

Mutations that have no effect on the amino acid produced by a codon.

Question 50

What are missense mutations?

Answer 50

Mutations that code for an amino acid, but not the correct amino acid.

Question 51

What are nonsense mutations?

Answer 51

Mutations that change an amino acid codon into a stop codon.

Question 52

What are insertions and deletions?

Answer 52

Additions or losses of nucleotide pairs in a gene.

Question 53

What is a frameshift mutation?

Answer 53

A mutation caused by insertion or deletion of nucleotides that alters the reading frame.

Question 54

What can spontaneous mutations occur during?

Answer 54

Errors in DNA replication or recombination.

Question 55

What are mutagens?

Answer 55

Physical or chemical agents that can cause mutations.

Question 56

What is the relationship between mutagens and carcinogens?

Answer 56

Most carcinogens are mutagens, and most mutagens are carcinogenic.

Question 57

What is CRISPR-Cas9?

Answer 57

A powerful technique for gene editing that is transforming genetic engineering.

Question 58

What does the Cas9 protein do?

Answer 58

Cuts any sequence to which it is targeted.

Question 59

How do researchers use CRISPR-Cas9 to treat genetic diseases?

Answer 59

By introducing a template with a normal copy of the gene to be corrected.

Question 60

What concerns exist about using CRISPR-Cas9 in humans?

Answer 60

Possibility of unintended effects on genes that have not been targeted.

Question 61

How has the definition of a gene evolved?

Answer 61

* A discrete unit of inheritance * A region of specific nucleotide sequence in a chromosome * A DNA sequence that codes for a specific polypeptide chain

Question 62

How can a gene be defined?

Answer 62

A region of DNA that can be expressed to produce a final functional product that is either a polypeptide or an RNA molecule.