8: Microbial Genetics

Question 1

Genetics

Answer 1

Total DNA contained within the cell

Question 2

What are Nucleotides of DNA composed of

Answer 2

Nitrogenous Base
Deoxyribose Sugar
Phosphate Group

Question 3

Four types of Nitrogenous Bases present in DNA

Answer 3

Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)

Question 4

How do A, T, G, and C pair

Answer 4

A base pairs with T via two hydrogen bonds
G base pairs with C via three hydrogen bonds

Question 5

What links adjacent nucleotides

Answer 5

Phosphodiester bonds

Question 6

What direction is DNA

Answer 6

Start at 5’, end at 3’

Question 7

Flow of Genetic Info

Answer 7

DNA replicates before division so that each offspring receives one complete copy of genome
DNA is used within cell to make proteins
DNA can flow b/w two different cells (recombination)

Question 8

DNA Replication

Answer 8

DNA gyrase and helicase unwind and separate the two DNA strands
A short RNA primer is synthesized by primase (RNA polymerase)
DNA synthesis occurs by DNA polymerase

Question 9

How does DNA polymerase work

Answer 9

It can only add nucleotides in 5’-3’ direction
Therefore it must read the template 3’-5’

Question 10

How are synthesizing the first and second strand different

Answer 10

The first is continuous and known as the leading strand
The second is discontinuous and known as the lagging strand

Question 11

Lagging strand synthesis

Answer 11

Since lagging strand must be made in 3’-5’ direction, the DNA polymerase synthesizes small parts at a time called Okazaki fragments
Fragments are joined by DNA ligase

Question 12

What are the three kinds of RNA and what are they used for

Answer 12

Messenger RNA to carry coded info for making proteins
Ribosomal RNA to form part of ribosomes where protein synthesis occurs
Transfer RNA to carry specific amino acids to the ribosomes to make protein

Question 13

What is transcription and what does it require

Answer 13

RNA is synthesized from a gene
mRNA is complimentary to the gene
U is used in place of T
Requires: RNA polymerase, RNA nucleotides, a DNA template

Question 14

What are the steps of transcription

Answer 14

1: RNA polymerase binds too DNA at a promoter
2: RNA polymerase assembles nucleotides into a new RNA chain
3: RNA polymerase moves along template as the new RNA chain grows
4: RNA polymerase reaches terminator
5: RNA polymerase and newly formed single stranded RNA are released

Question 15

What is translation

Answer 15

Info (codons) in mRNA is translated to make proteins

Question 16

What are the steps of translation

Answer 16

1: mRNA attaches to ribosome
2: tRNA carrying amino acid enters ribosome and binds to mRNA
3: the next tRNA with amino acid enters the ribosome and binds to the mRNA
4: Two amino acids are joined by a peptide bond
5: Ribosome repeats until a stop codon
6: mRNA and protein are released from the ribosome

Question 17

Point Mutation

Answer 17

A single nucleotide is replaced with another
If it leads to an incorrect amino acid in protein, called missense mutation
If it leads to the same amino acid, called redundant genetic code
If it leads to a stop codon, protein is cut short and called a truncated protein

Question 18

Frameshift Mutation

Answer 18

Insertion: extra nucleotide is added
Deletion: nucleotide is removed

Question 19

How do mutations occur

Answer 19

Spontaneous Mutations: Occasional mistakes (very unlikely)
Mutagens: Agents which bring about mutations, UV light, radiation, chemicals

Question 20

Plasmids

Answer 20

Self-replicating double stranded DNA molecules
Contain non-essential genes, such as resistance to penicillin

Question 21

F plasmids

Answer 21

Fertility plasmid
Carry genes to make F pili
Involved in conjugation
F+ grows pili and can share, F- cannot, but can change to F+

Question 22

R plasmids

Answer 22

Resistance factors
Carry genes for antibiotic resistance

Question 23

Vir plasmids

Answer 23

Virulence factors
Carry genes for toxin production

Question 24

What are the three ways genetic material can be transferred between bacterial cells

Answer 24

Transformation
Conjugation
Transduction

Question 25

Transformation

Answer 25

Uptake of naked DNA It can come from dead cells or from released plasmids Pieces can be integrated into the chromosome, which is called recombination

Question 26

Conjugation

Answer 26

Bacterial mating Male F pili (F+) is a donor with appendage Female F- is a recipient A copy of F plasmid is transferred and F- becomes F+

Question 27

Transduction

Answer 27

Small fragments of DNA are transferred between bacteria via a virus (bacteriophage) 1: Phage injects DNA into cell 2: Phage DNA is replicated within cell 3: New Phages are synthesized and assembled These new Phages can infect another bacterial cell