Module 5 Microbial Genetics-Replication EXAM 2 Flashcards
Genetics-Replication-Transcription-Translation-Mutations-Genetic Transfer
DNA replication happens?
prior to cell division
DNA holds?
the hereditary information in the form of genes,
DNA is made up of?
DNA is made up of nucleotides
The genetic sequence of DNA is?
the genetic information is held within the particular sequence of A,T,C and G in the DNA
DNA genes are?
genes are specific sequences on the DNA that code for making a particular protein
What is the structure of DNA?
Each nucleotide consists of 3 parts:
Deoxyribose sugar; 5 carbon sugar (pentose)
Phosphate group
Nitrogenous base
Purines: adenine, guanine
Pyrimidines: thymine, cytosine
Pyrimidines are cut, only one
Nucleotides are linked together by a covalent backbone to make the polymers, explain the link and bond:
The sugar of one nucleotide is linked to the phosphate group of the next nucleotide through a phosphodiester bond. This bond forms between the 5’ carbon of the sugar of one nucleotide and the phosphate group, and the 3’ carbon of the sugar of the adjacent nucleotide.
DNA is a ________________, strands are ______________________.
double stranded helix, antiparallel (Antiparallel means they run in different directions)
What are handrails of step ladder made of?
Sugar and phosphate phosphodiester bonds
What is the DNA held together by?
Hydrogen bonds
What are the rungs (steps) of the step ladder made of?
Complementary base pairing
A makes 2 hydrogen bonds to T
G makes 3 hydrogen bonds to C
Eukaryotic DNA:
vary in number from a few to hundreds, linear, associated with histone proteins, have nucleus, diploid or haploid
Prokaryotic DNA:
single, circular, condensed and secured by means of histone-like proteins (NOT HISTONE but histone-LIKE)
Where does DNA replication occur in eukaryotes?
Eukaryotes: nucleus
Where does DNA replication occur in prokaryotes?
Prokaryotes: cytoplasm
What are the enzymes involved in DNA replication?
Helicase, topoisomerase, single stranded binding proteins, primase, DNA polymerase III, DNA polymerase I, ligase
Helicase
unwinds and zips the DNA double helix
Topoisomerase
enzyme that proceeds ahead of the replication fork to relax or prevent supercoiling
Single stranded binding proteins
stabilize open DNA; keep double stranded DNA from reforming - keep it single stranded; protect DNA from degrading
RNA Primase
makes a small RNA fragment (primer) with a 3’ OH for a DNA nucleotide to bind to new strand must be 5’ to 3’)
DNA polymerase III
main replication enzyme; adds nucleotides to the growing DNA strand in a 5’ to 3’ direction
DNA polymerase I
removes the RNA primer and replaces it with DNA nucleotides in a 5’ to 3’ direction
Ligase
seals Okazaki fragments together
What is direction does exonuclease go for DNA polymerases?
DNA polymerase III has 3’to 5’ exonuclease activity
This means that it can go backwards to take out a mistake; think of this as “proof reading”
What is Polymerase direction?
DNA polymerases add nucleotides to the growing DNA strand at the 3’ end, meaning that DNA synthesis always occurs in the 5’ to 3’ direction.
how does replication occurs on the leading strand?
Along one template strand of DNA, the DNA polymerase synthesizes the leading strand continuously, moving toward the replication fork
how does replication occurs on the lagging strand?
To elongate the other new strand called the lagging strand, DNA polymerase must work in the direction away from the replication fork
Lagging strand is synthesized as a series of Okazaki fragments, which are joined together by DNA ligase
How can mutation occur?
Mutations are changes in the DNA sequence that can occur spontaneously (randomly) or due to external factors like radiation, chemicals, or viruses
What is a point mutation and what are the different types of point mutations?
Point mutations: substitution of 1 nucleotide
Types: Silent Mutation, Missense Mutation, Nonsense Mutation
Silent Mutation
Silent Mutation: change in a single nucleotide that does not alter the sequence; the same protein is produced
Has no effect on the proteins functioning
Example: UUU changes to UUC (both Phe)
Missense Mutation
Missense Mutation: The protein produced will have one amino acid substituted with another
Variable impact—can be neutral, mildly harmful, or severely damaging
Example: UUU to UUA changes the dictionary code of one amino acid in codon
Nonsense mutation
Nonsense mutation: A change in a single nucleotide that converts a codon into a stop codon–this causes premature termination of a protein synthesis
Generally results in a nonfunctional protein
What is a frameshift mutation? how it occurs and how does it effect the outcome of the protein produced?
addition or deletion, reading frame is altered (whole sequence changes)
Most serious type of mutation
resulting in a completely different amino acid sequence being produced from that point onwards, usually leading to a nonfunctional protein due to the drastic change in structure and function
Gene expression is
The process by which DNA directs protein synthesis
What 2 stages does gene expression include?
transcription and translation (A way to remember transcription comes before translation is that there is a “C” in transcription which comes before the “L” in translation in the alphabet)
Why do we do it this way? Why not just use DNA as the final product?
DNAs primary purpose is to store genetic information; Proteins actually carry out cellular functions, they are the actual workers
Where is does the process of Transcription occur in eukaryotes?
Occurs in eukaryotes nucleus
Where is does the process of Transcription occur in prokaryotes?
Occurs in prokaryotes cytoplasm
Where is does the process of Transcription begin?
Begins at the start site (+1) within the promoter region
Promoter is where RNA polymerase binds and starts copying the DNA sequence into messenger RNA (mRNA). This occurs at the start site +1 within the promoter, upstream of the gene being transcribed.
What direction does the process of Transcription occur?
Newly synthesized RNA molecules are synthesized in a 5’ to 3’ direction
Reads DNA template that is 3’ to 5’
What enzymes are involved in transcription?
RNA polymerase
What strand of DNA is used as template?
The template strand of DNA is transcribed into the mRNA sequence
What strand of DNA is used as coding?
The coding strand has the same sequence as the transcribed mRNA (with the T being replaced by U)
What are the 4 unique things only found in eukaryotic mRNA processing?
5’ Cap, Poly A Tail, Introns, Exons
5’ Cap
Only in eukaryotes
modified guanine that has a methyl attached to it; tells ribosome what end to start on
Poly A TailOnly in eukaryotes
Only in eukaryotes
a bunch of adenines; degrading enzymes will start here instead of degrading the amino acid sequence
Introns
Only in eukaryotes
non-coding sequences, removed before translation by RNA splicing- intervening sequences
Exons
Only in eukaryotes
the portion of the RNA that gets expressed
What are the 3 different types of RNA?
mRNA: messenger RNA, tRNA: transfer RNA, rRNA: ribosomal RNA
What is the function of: mRNA: messenger RNA
Contains codes for sequence of amino acids in protein; carries the DNA master code to the ribosome
What is the function of: tRNA: transfer RNA
Brings amino acids to ribosome during translation
What is the function of: rRNA: ribosomal RNA
Forms the major part of a ribosome and participates in protein synthesis
What is a codon?
Three RNA nucleotides that code for one amino acid of a protein
What is the genetic code dictionary?
Determines the amino acid sequence of a protein from a strand of mRNA
Translation is when:
mRNA translated into polypeptide
Where does translation occur for eukaryotes and prokaryotes?
Happens on ribosomes in the cytoplasm of prokaryotes and eukaryotes; can happen in ribosomes in rough ER in eukaryotes
Where does translation begin?
Starts at the start codon, usually AUG
What direction does translation occur?
Occurs in a 5’ to 3’ direction
What is the function of the A site?
A site: holds new incoming amino acid
What is the function of the P site?
P site: tRNA will bind here first in the ribosome; holds growing peptide or protein chain
Describe the Codon/anticodon interaction
tRNA anticodon binds to mRNA codon in an anitparallel manner
So, if mRNA is a 5’-3’ direction, the tRNA will bind its 5’ end to the 3’ end of the mRNA
What is the function of the E site?
E site: empty; tRNA can exit
What is an anticodon?
An anticodon is the complementary sequence on the tRNA that binds to the mRNA codon
H-bond temporarily with the mRNA codon just long enough to drop off the correct amino acid
Where does the process stop?
Process stops at the STOP codon
What are polyribosomes?
polyribosomes are clusters of ribosomes working together on a single strand of mRNA to efficiently produce many copies of a protein, speeding up the process of translation.
What is meant by the genetic code being redundant?
Multiple codons can code for the same amino acid. While there are 64 possible codons, there are only 20 amino acids that need to be coded for in proteins. This means that some amino acids are specified by more than one codon.
Redundancy helps protect against mutations
The _____________________ of the protein (and therefore, the gene sequence in the DNA) is what makes each protein________________ from all the other proteins in your body
amino acid sequence, different
What is the “wobble hypothesis”?
The wobble hypothesis explains how cells can use fewer tRNA molecules to read the genetic code during protein synthesis. Normally, a tRNA molecule pairs with a codon (a three-letter sequence of mRNA) to add an amino acid to the growing protein.
The first two letters of the codon match perfectly with the tRNA, but the third letter is more flexible, or “wobbly.” This flexibility means one tRNA can recognize multiple codons that differ only in the third position, allowing cells to make proteins more efficiently.*
Operons:
more than one gene all regulated as a whole
Inducible:
usually “off” but can be turned “on” in response to a specific inducer molecule (Ex: lac-operon: lactose, glucose)
Repressible:
usually “on” but can be turned “off” when a specific corepressor binds to the repressor protein (ex: arginine)
What are the 3 types of genetic transfer?
transformation, transduction and conjugation
Transformation
Transfer type: Indirect
Factors: Free Donor DNA
Genes transferred: capsule formation
Transduction
Transfer type: Indirect
Factors: DNA transferred via a virus
Genes transferred: toxins, drug resistance
2 types:
Generalized Transduction: random fragments from disintegrating DNA are picked up by phage
Specialized Transduction: highly specific part of host genome is regularly incorporated into virus (ex: streptococcus pyogenes gains toxin for scarlet fever)
Conjugation
Transfer type: Direct
Factors: DNA transferred via a sex pili
Genes transferred: toxins, drug resistance
