Chapter 8 Microbial Genetics Flashcards
Define genetics.
The study of what genes are, how they carry information, how information is expressed, and how genes are replicated
What is a gene?
A gene is a segment of DNA that encodes a functional product, usually a protein
What is a chromosome?
Structure containing DNA that physically carries hereditary information; the chromosomes contain the genes
What is a genome?
All the genetic information in a cell
What is genomics?
The molecular study of genomes
What is a genotype?
The genes of an organism
What is a phenotype?
Expression of the genes
What does it mean when a gene is express or turned on?
Means the gene product (protein is made)
What is recombination when referring to the flow of genetic information?
Recombination is genetic information can can be transferred between cells of the same generation.
Horizontally
What is the passing of genetic information vertically called?
Replication
DNA is made of polymers of nucleotides, what are they and how do they pair?
Adenine to Thymine
Cytosine to Guanine
What is the backbone of DNA made of?
How are they formed in space
Alternating Sugar-phosphate groups that are held together by hydrogen bonds between AT and CG
The strands are antiparallel
What is semi conservative DNA replication?
Means one strand is old and one strand is new
What is DNA polymerase? What does it do and in what direction does it do it?
It’s an enzyme that adds new nucleotides to the 3’ end and ligament act as a glue.
This happens in the 5’ to 3’ direction
What is the template strand?
How is this done?
The base sequence that determines the base sequence in the other strand
This is done by complementary base paring
What makes replications very accurate and why?
It’s accurate due to proof reading by polymerase
How is the leading strand copied and by what enzyme?
The leading strand is synthesized continuously by DNA polymerase
How is the lagging strand synthesized, and what enzyme is responsible for its synthesis? What is the product?
The laggin strand is synthesized discontinuously.
RNA polymerase synthesizes a short RNA primer, which is then extended by DNA polymerase.
What does DNA polymerase do in the lagging strand?
It digest RNA primers replacing them with DNA leaving fragmented pieces.
What are the fragments that DNA polymerase leaves behind. How is this fixed?
Okazaki fragments
DNA ligase joins the discontinuous fragments of the lagging strand
What do genes make and what are they responsible for?
Genes make proteins
Genes are responsible for traits
What is a segment of DNA that specifies a sequence of amino acids in a protein
Genes
What are the two mechanisms that carry out protein synthesis?
Transcription and Translation
What is the generic sequence of events that occur with transcription and translation?
Transcription: mRNA is transcribe (copied) from DNA
Translation: mRNA makes protein
DNA is transcribed to make what?
When does this begin and what starts this process?
DNA is transcribed into mRNA
Transcription begins with RNA polymerase bind to the promoter sequence on DNA
Which direction does transcription proceed in?
When does it stop
5’ to 3’
Transcription stops when it reaches a terminator sequence
What is genetic code and what is it called
Genetic code is Triplet Code
Each is a 3-nucleotide of mRNA and is called a Codon
How many sense codons are there and how many non sense codons are there?
61 sense codons
3 nonsense (stop) codons
What is the start codon and what AA is it?
What are the 3 nonsense codons (stop codons)
AUG start codon and its Methionine
Stop codons UAA, UAG, UGA
What are snRNP’s?
What else does what snRNP’s do?
SnRNP’s are small nuclear ribonucleoproteins that excise out the introns and splice together the exon-derived RNA in to mRNA which then leave the nucleus as mRNA
Ribozyme
What are exons?
Real genes
What specifies the order of the amino acids in a protein?
Sequence of codon in mRNA
What is tRNA and what is its function?
Has the anticodon i.e. The 3 complementary bases to the mRNA. This carries the amino acids that will be joined to the growing polypeptide chain
What is are the three sites with a ribosome? Which site is the start site, the site that the incoming tRNA waits in, and the site were the tRNA leaves?
The P site is where it begins.
The A site is where the peptide bond forms and the incoming tRNA waits.
The E site is where the empty tRNA leaves the ribosome.
This process of a growing polypeptide is called what and what is its function?
Translation and its forming a protein
What is the start codon and what is its AA?
What are the three stop nonsense codons?
AUG = methionine
UAA UAG UGA
What are the three steps to Translation?
Initiation
Elongation
Termination
How do we regulated bacterial gene expression?
By controlling enzymes, if we don’t need them, we shouldn’t make them.
What are the two genetic control mechanisms that regulate Pre-transcriptional control?
Repression
Induction
What are Constitutive genes?
These are genes that are expressed at a fixed rate
Ex. Enzymes in Glycolysis
Who discovered the Operon Structure?
Jacob and Monod 1961
What is an Operon?
The combination of several genes which are located side-by-side on DNA and work together.
A set of operator and promoter sites and structural genes that defines and operon
What are Structure Genes?
They determine the structure of the protein
What is the promoter (P)?
Site for RNA polymerase attachment
What is the operator (O)?
Site for Repressor molecule to attach
What are Regulatory Genes?
Makes Repressor molecule.
The I gene that encodes for a repressor that switches inducible and repressible operons on and off.
What are the two types of operons?
Give example and if on or off
Inducible operons: are not usually transcribed (OFF) meaning must be turned on
Example: Lac Operon
Repressive operons: operate in reverse fashion- they transcribe continually until turned (off) by repressors. They are always turned on.
Example: Tryptophan Operon
What is an inducer and what is its function?
Inducers control Induction
Enzymes are called Inducible Enzymes bind to the repress or protein and inactive it allowing RNA Polymerase to bind and transcription of the gene to occur, which forms mRNA.
What is repression. How does it work in the presence of Tryptophan?
Inhibits gene expression, which is controlled by a Repressor molecule.
Tryptophan attaches to an inactive repressor protein which activates it. It then blocks the binding site for RNA polymerase. This is similar to a feed-back mechanism
Regulation of the Lac Operon also depends on concentration of what compound?
Glucose
Explain the glucose effect. What happens when glucose is not present?
What type of regulation is this?
When glucose is not available, cells will produce cAMP in high amounts. -cAMP then binds to a protein called a Catabolite Activator Protein (CAP)
this complex binds to the Lac Promoter which is required for RNA Polymerase to bind and of transcription to proceed.
This is positive regulation
What is cAMP?
Is an example of alarmone, which a chemical like hormone.
What happens when lactose is present and glucose is present?
-cAMP is not generated and the CAP remains inactivated, therefore RNA Polymerase can not bind and transcription does not occur.
What happens in the presence of Glucose?
If glucose is present, it is used up first, which produces a lag time then the lactose is used up turning on Transcription because cAMP is then produced
What is a mutation? What does it cause
A permeant change in the base sequence of DNA, which creates a change in AA sequence of a protein
What does a mutation cause?
Mutations may be neutral (silent), beneficial, or harmful
What is a Mutagen?
Agent that causes mutations
What is Spontaneous mutations?
These occur in the absence of mutagen
What are the types of mutations?
Base substitution
Missense mutation
Nonsense mutation
Frameshift mutation
What is a base substitution?
What does this lead to?
It is a change in one base sequence called a (point mutation)
This can cause the wrong base to be inserted and therefore code for the wrong protein. This causes missense mutations
What does a Missense mutation cause?
Give an example
If a base substitution causes a change in AA then Missense mutation occurs.
An example is Sickle-cell disease
What is Nonsense mutation?
A base substitution can cause a nonsense mutation which results in a stop codon (UAA, UAG, UGA) to be made and therefor an incomplete portion is made
What is a Frameshift mutation?
Give an example?
This is the insertion or deletion of one or more nucleotide pairs. This shifts the translational reading frame of a triplet codon (three nucleotides)
The result is an inactive protein that is made.
Huntingtons Disease which is caused by the insertion of extra base-pairs
What are chemical mutagens?
Agents in the environment such as chemicals or radiation that directly or indirectly bring about mutations.
What is a chemical mutagen (example)?
Nucleoside analog (base analog)
What is Nucleoside (base) analog?
Give and example and it effect
Analogs are structurally similar to normal bases.
Adenine nucleoside becomes 2-Aminopurine nucleoside
This is incorporated into DNA in place of the adenine but can pair with cytosine, so AT becomes CG
What does Radiation as a mutagen cause? What gives off this radiation?
Ionizing radiation (X-rays and gamma rays) are potent mutagens
U.V. Light (260 nm) damages DNA
Basically way too much sun light can cause cancer.
What does radiation do to DNA? What does it form?
UV radiation cause Thymine dimers
How are thymine diners repaired?
By photolyases that separate thymine dimers, this is done in plants.
In humans is nucleotide excision repair.
Define Nucleotide excision repair?
An endonuclease cuts the DNA removing the dimer, then DNA polymerase fills the gap by using the intact strand as a template
