Chapter 8

Question 1

What is a gene, and what does it code for?

Answer 1

A gene is a segment of DNA that codes for functional products.

Question 2

What are chromosomes, and what do they physically carry?

Answer 2

Chromosomes are structures containing DNA that physically carry hereditary information.

Question 3

What is the genetic material in bacteria, and what is its structure?

Answer 3

The genetic material in bacteria is a singular circular chromosome, and it contains short tandem repeats (STRs), which are repeating sequences of noncoding DNA.

Question 4

What are the three parts of a nucleotide?

Answer 4

A nucleotide consists of three parts: a sugar molecule (deoxyribose in DNA or ribose in RNA), a phosphate group, and a nitrogenous base.

Question 5

What are the two types of nucleic acid?

Answer 5

The two types of nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

Question 6

What are the four types of nitrogenous bases used in DNA?

Answer 6

The four nitrogenous bases used in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G).

In RNA, Thymine is replaced with Uracil. Uracil binds with adenine(A).

Question 7

What is the leading strand in DNA replication, and how is it synthesized?

Answer 7

The leading strand is synthesized continuously by DNA polymerase in the 5’ to 3’ direction.

Question 8

What is semiconservative replication?

Answer 8

Semiconservative replication is a process in which each newly synthesized DNA molecule consists of one original (parental) strand and one newly synthesized strand. This ensures that the genetic information is preserved during replication.

Question 9

What is the lagging strand in DNA replication, and how is it synthesized?

Answer 9

The lagging strand is synthesized discontinuously, with initiation by an RNA primer. This process creates Okazaki fragments, which are later joined by DNA polymerase and DNA ligase.

Question 10

What is RNA, and how does it differ from DNA in terms of structure?

Answer 10

RNA is a single-stranded nucleotide that contains a 5-carbon ribose sugar. It contains uracil (U) instead of thymine (T) found in DNA.

Question 11

What is transcription, and what are its stages?

Answer 11

• Transcription is making mRNA from DNA.
• The stages are initiation (start), elongation (making mRNA), and termination (stop).

Question 12

Where does transcription happen in eukaryotes, and what happens to mRNA before it leaves the nucleus?

Answer 12

In eukaryotes, transcription occurs in the nucleus. Before leaving, mRNA is processed to remove non-coding parts (introns) and join the coding parts (exons).

In prokaryotes, transcription occurs in the cytoplasm.

Question 13

How is genetic information encoded in mRNA, and what are codons?

Answer 13

• mRNA uses codons (groups of three letters) to carry genetic information.
• There are 64 codons for 20 amino acids due to degeneracy, where multiple codons can mean one amino acid.

Question 14

What is the first amino acid? What is the codon for this amino acid?

Answer 14

The first amino acid is Methonine. The codon is AUG. This is the start codon.

Question 15

What are the three stop codons? Why do these codons cause translation to end?

Answer 15

1. UAA
2. UAG
3. UGA
   They are known as nonsense codons and cause translation to stop because the ribosome reads the nonsense codon and releases it, forming a protein.

Question 16

What are the types of base subsitutions (point mutation)?

Answer 16

1. Missense mutation: base substitution results in change in amino acid
2. Nonsense mutation: base substitution results in a nonsense (stop) codon
3. Frameshift mutation: Insertion or deletion of one or more nucleotride pairs

Question 17

Where does translation happen, and how is the mRNA code turned into proteins?

Answer 17

• Translation occurs in ribosomes.
• It reads mRNA codons, adds amino acids, and builds a protein chain.
• tRNA molecules with anticodons bring the right amino acids. In bacteria, translation can start before transcription is done.

Question 18

What is a mutation in DNA?

Answer 18

A mutation is a change in the DNA’s base sequence.

Question 19

How can a mutation in a gene affect the enzyme it encodes?

Answer 19

A gene mutation can make the enzyme inactive, less active, or even enhance its activity.

Question 20

What is a base substitution mutation, and what are the types of such mutations?

Answer 20

A base substitution mutation is when one base in DNA changes. Types include:

Missense mutation: Changes an amino acid.
Nonsense mutation: Creates a stop codon.
Frameshift mutation: Inserts or deletes nucleotide pairs, shifting the reading frame.

Question 21

What are silent mutations, and why might they not affect protein function?

Answer 21

Silent mutations change DNA but may not impact protein function because:

The genetic code’s redundancy may still code for the same amino acid.
The mutation may occur in a non-critical part of the protein.
The changed amino acid may be chemically similar to the original.

Question 22

What are chemical mutagens, and how do they cause mutations?

Answer 22

• Chemical mutagens:
  Nitrous acid and nucleoside analogs, induce mutations by altering base pairing/ replacing normal bases, leading to base pairing errors.
• Frameshift mutagens, such as benzopyrene, can also cause mutations.

Question 23

How does radiation cause DNA mutations, and what’s an example?

Answer 23

Radiation, particularly ionizing radiation (like X-rays and gamma rays), can damage DNA by forming ions that oxidize nucleotides and break DNA strands.

Question 24

How does UV radiation induce mutations, and what are thymine dimers?

Answer 24

UV radiation causes mutations by creating thymine dimers, where adjacent thymine bases bind together, disrupting DNA structure.

Question 25

What are two ways DNA can be mutated?

Answer 25

1. Spontaneous mutations (DNA polymerase didn’t do a great job proofreading)
2. Mutagens (environmental factors like radiation and certain chemicals).

Question 26

What are the enzymes that can repair mutation damage?

Answer 26

1. Photolyases: separate thymine dimers (repairs UV damage)
2. Nucleotide excision repair: Enzymes cut out incorrect bases and fill in correct bases

Question 27

What is the baseline error rate for DNA polymerase?

Answer 27

1/1 Million (10^6)

Question 28

What is the error rate for DNA polymerase once mutagens are added into the picture?

Answer 28

Increases rate to 1/1 Thousand

Question 29

What is the difference between horizontal and vertical gene transfer?

Answer 29

• Vertical gene transfer: transfer of genes from an organism to its offspring
• Horizontal gene transfer: transfer of genes between cells of the same generation

The difference is that vertical gives genes to its “kids” whereas horizontal gives genes to “brothers” or “sisters”

Question 30

Which type of gene transfer
can humans do?

Answer 30

Humans can do vertical gene transfer.

Question 31

Where does DNA come from in transformation? Do cells need to be in contact for transformation?

Answer 31

In transformation, DNA comes from lysed or dead cells. The cell does not need to be in contact for transformation. It picks up the “naked” DNA from lysed/dead cells.

Question 32

Genetic Recombination

What is genetic recombination, and what role does it play?

Answer 32

Genetic recombination contributes to genetic diversity within populations and can introduce new functions into organisms.

Question 33

Genetic Recombination

When does genetic recombination typically occur in a cell?

Answer 33

Genetic recombination occurs after foreign DNA has entered a cell.

Question 34

Genetic Recombination

What are the four mechanisms of genetic recombination?

Answer 34

1. Transformation (DNA from lysed/dead cells make its way into another cell)
2. Transduction
3. Conjugation (Plasmid replicates from a F+ cell, then gives replicated plasmid to a F- cell)
4. Transposons

Question 35

Genetic Recombination

Explain how transduction works.

Answer 35

• Transduction involves the transfer of DNA from a donor cell to a recipient via a bacteriophage.
• There are two types: generalized transduction and specialized transduction.

Question 36

Genetic Recombination

What is conjugation, and what is required for it to occur?

Answer 36

Conjugation is the transfer of plasmids from one bacterium to another, requiring cell-to-cell contact via sex pili and compatibility of mating types.

Question 37

Genetic Recombination

In conjugation, which cell structure transfers the plasmid from one cell to another?

Answer 37

The sex pilli

Question 38

Genetic Recombination

What happens to the recipient cell after conjugation is complete with a Hfr cell?

Answer 38

When an Hfr donor passes a portion of its chromosome into an F– recipient, a recombinant F– cell results.

Question 39

Genetic Recombination

What is transferred during conjugation with an Hfr cell?

Answer 39

A portion of the Hfr chromosome is transferred to the recipient cell.

Question 40

Genetic Recombination

What is a transpon?

Answer 40

• Transposons are segments of DNA that can move within the genome. They contain insertion sequences (IS) that code for transposase, allowing them to cut and reseal DNA.
• Complex transposons may carry additional genes, including those related to antibiotic resistance.

Question 41

DNA uses what enzyme for replication?
During the process of transcription, what enzyme does RNA use?

Answer 41

• DNA uses DNA polymerase
• Transcription uses RNA polymerase

Question 42

What is constitutive gene expression? What is inducible gene expression?

Answer 42

• Constitutive gene expression is when we always need to make enzymes no matter the scenerio. (We are always making proteins.)
• Inducible gene expression is when we make enzymes for specific situations.