Micro Lecture Bacterial Genetics Exam 2

how many chromosomes does a bacterial genome have and what is the shape

one circular chromosome

where is the chromosome located in a bacterial genome

the nucleoid region

do eukaryotic genes or bacteria genes have introns

eukaryotic genes

can bacteria contain plasmids

yes

what is the shape and number of eukaryotic chromosomes

multiple, linear chromosomes

where is DNA located in a eukaryotic cell

the nucleus

do eukaryotes or bacteria have more non-coding DNA

eukaryotes

what is a plasmid. is it essential DNA and can it replicate independently or does it use something to replicate

a small, circular molecule of non-essential DNA that can replicate independently.

Plasmids can carry genes that give bacteria a

survival advantage

R plasmids can carry

antibiotic resistant genes

Plasmids can be transferred between bacteria through

horizontal gene transfer

Bidirectional means

replication proceeds in two directions from the origin of replication.

Semiconservative means

each new DNA molecule contains:

• 1 original/parental strand

• 1 newly synthesized strand

Replication begins at the

origin of replication

what enzyme separates the two DNA strands.

helicase

steps to the initiation phase of DNA synthesis

Initiation

• Replication begins at the origin of replication

• Helicase separates the DNA strands

• This creates a replication bubble

• Primase creates a short RNA primer

what does primase do

Makes RNA primer

elongation phase steps of DNA synthesis

Elongation

• DNA polymerase III adds DNA nucleotides

• DNA polymerase I removes RNA primers and replaces them with DNA

• DNA ligase connects the DNA fragments

what does DNA polymerase III do

adds DNA nucleotides

DNA can only be synthesized from what primes

5’—→3’

the lagging strand is

• synthesized discontinuously as Okazaki fragments

the leading strand is synthesized

continuously

what does DNA polymerase I do

Removes RNA primers and replaces them with DNA

what does ligase do

• connects the DNA fragments

termination phase of DNA synthesis

Termination

• Replication ends at the terminus (ter) site

• Two identical copies of DNA have been produced. 

what does DNA gyrase do

controls DNA supercoiling

what is a mutation

a permanent, heritable change in a DNA sequence. 

3 causes of DNA mutations

• Replication errors

• X-rays

• UV radiation

what is missense mutation and what does it result in

• One base is changed

• Results in a different amino acid being coded for

what is nonsense mutation and what is the result

• A mutation creates a stop codon

• Causes translation to stop early

what is insertion frameshift mutation and what is the result

• A nucleotide is added

• Shifts the reading frame

what is deletion frameshift and what is the result

• A nucleotide is removed

• Shifts the reading frame

mRNA stands for

messenger RNA

rRNA stands for

ribosomal RNA

tRNA stands for

transfer RNA

what does mRNA do

• Carries genetic information

• Provides the sequence that the ribosome uses to make a protein

what does rRNA do

• Makes up part of the ribosome

• Helps with translation

what does tRNA do

• Carries amino acids to the ribosome

• Has an anticodon that recognizes a complementary mRNA codon

what does the sigma factor do

 helps RNA polymerase recognize and bind to the promoter.

transcription turns DNA into

RNA

steps to transcription (7)

1. Sigma factor helps RNA polymerase recognize and bind to the promoter.

2. RNA polymerase begins transcription.

3. Sigma factor dissociates.

4. RNA polymerase uses the 3′ → 5′ DNA strand as the template.

5. RNA is synthesized 5′ → 3′.

6. RNA polymerase reaches a termination/pause site.

7. mRNA is released. 

in bacteria can transcription and translation occur at the same time? why or why not

yes because  Bacteria do not have a nucleus separating DNA from ribosomes. As mRNA is being produced, ribosomes can begin translating it into protein

where does transcription occur in eukaryotes

the nucleus

where does translation occur in eukaryotes

the cytoplasm

what are the steps to initiation in translation

Initiation

• Ribosome recognizes the ribosome-binding site (RBS)

• mRNA is positioned correctly

• AUG is the start codon

• Formyl-Met tRNA binds to AUG

• 50S subunit joins the 30S subunit

• Ribosome now has the A, P, and E sites. 

what are the steps to elongation in translation

Elongation

• tRNAs bring amino acids

• tRNA anticodons pair with mRNA codons

• Amino acids are joined together

• Polypeptide chain grows. 

what are the steps to termination in translation

Termination

• Ribosome reaches a stop codon

• Stop codons = UAA, UAG, UGA

• No tRNA matches a stop codon

• A release factor enters the A site

• Translation ends. 

what are the targets for antibiotics that inhibit bacterial protein synthesis. 

the 30S and 50S ribosomal subunits

example of how antibiotics target protein synthesis

Doxycycline → 30S ribosomal subunit → blocks the A site → inhibits protein synthesis

what does transcriptional control do

Controls whether mRNA is produced.

what does transcriptional control involve

• Repressors

• Activators

• Alternative sigma factors

what does translational control do

Controls whether an mRNA is translated into protein.

what does post translational control do

Controls proteins after they are made.

proteins can be ___, ___, or ___ in post translational control

• Activated

• Deactivated

• Degraded

why do bacteria regulate gene expression

to save energy because bacteria don't want to waste energy producing proteins they don't need.

what does Inducible mean

normally off

The lac operon is involved in

catabolic reactions involving lactose.

how does the lac operon work with no lactose

• Repressor is active

• Repressor binds the operator

• Transcription is blocked

how does the lac operon work with lactose present

• Lactose acts as an inducer

• Inducer binds to the repressor

• Repressor becomes inactive

• Repressor cannot bind the operator

• Transcription occurs.

Repressible mean

normally on

The trp operon is involved in

anabolic reactions that make tryptophan.

how does the trp operon work with low tryptophan

• Repressor is inactive

• Transcription occurs

how does the trp operon work with a lot of tryptophan

• Tryptophan acts as a corepressor

• Activates the repressor

• Repressor binds the operator

• Transcription stops.

how does DNA transfer occur in transformation

Bacteria take up extracellular DNA from their surroundings.

how does DNA transfer occur in conjugation

DNA transfers from one bacterium to another through cell-to-cell contact.

what 2 things does conjugation usually involve

• F plasmid

• Sex pilus

how does DNA transfer occur in transduction

A bacteriophage transfers bacterial DNA from one bacterium to another.

Describe the steps involved in PCR

• Step 1: Denaturation → Heat the DNA to 95°C to separate the two DNA strands.

• Step 2: Annealing → Lower the temperature to 55°C so DNA primers attach to the target DNA.

• Step 3: Extension → Raise the temperature to 72°C so heat-tolerant Taq DNA polymerase adds nucleotides and makes new DNA.

how many cycles do the steps in PCR go through

about 30-40

what are the beneficial applications of PCR (5)

• detecting pathogens, detecting antibiotic-resistance genes, identifying organisms that cannot be cultured, crime-scene DNA analysis, and genetic screening. 

Genetic sequencing determines the

exact nucleotide sequence of DNA

In the original Sanger method, DNA is copied using

 fluorescently labeled ddNTPs.

When a ddNTP is added

DNA elongation stops

The DNA fragments are separated by ___, and the fluorescent tags show which ___ occurs at each position.

length; nucleotide

beneficial applications of genetic sequencing (4)

identifying microbes in an environment, identifying genetic polymorphisms associated with disease, forensic identification, and paternity testing.

Recombinant DNA is DNA that contains

• sequences from different sources. 

Explain the steps necessary to engineer a human gene into a bacterial plasmid. (6)

1. Obtain the human gene of interest.

2. Remove introns from the eukaryotic gene.

3. Isolate RNA from human cells and use reverse transcriptase to convert the RNA into DNA.

4. Insert the human DNA sequence into a bacterial plasmid.

5. The plasmid is designed with bacterial components such as a promoter, operator, terminator, origin of replication, selectable marker, and Shine-Dalgarno sequence.

6. Put the recombinant plasmid into bacteria through transformation. 

 explain how a recombinant DNA plasmid expressing the insulin gene could produce human insulin.

• First, the recombinant plasmid containing the human insulin gene is introduced into E. coli through transformation.

• The plasmid undergoes DNA replication, allowing the bacteria to maintain and copy the insulin gene.

• The insulin gene undergoes transcription, producing mRNA.

• The mRNA undergoes translation at the bacterial ribosome, producing the human insulin protein.

• The bacteria can therefore act as “factories” to produce human insulin.