Chapter 11: Mechanisms of Microbial Genetics Flashcards
Gene Expression
The synthesis of a specific protein with a sequence of amino acids that is encoded in the gene.
Central Dogma
States that DNA encodes messenger RNA, which, in turn, encodes protein.
Semiconservative Replication
The two strands of the double helix separate during DNA replication, and each strand serves as a template from which the new complementary strand is copied.
DNA pol III
Adds deoxyribonucleotides each complementary to a nucleotide on the template strand, one by one to the 3’-OH group of the growing DNA chain.
DNA Gyrase/Topoisomerase II
Relaxes supercoiled chromosome to make DNA more accessible for the initiation of replication; helps relieve the stress of DNA when unwinding, by causing breaks and then resealing the DNA.
Helicase
Opens the DNA helix by breaking hydrogen bonds between the nitrogenous bases.
Primer
An RNA sequence 5-10 nucleotides long and complementary to the parental or template DNA that provides the free 3’OH end for DNA pol III.
RNA Polymerases
Do not need a free 3’-OH group to synthesize an RNA molecule.
Leading Strand
The continuously synthesized strand.
Okazaki Fragments
Small DNA fragments each separated by RNA primers.
Lagging Strand
The discontinuous strand with the Okazaki fragments.
Sliding Clamp
A ring-shaped protein that holds the DNA polymerase in place as it continues to add nucleotides.
Topoisomerase
Prevents the overwinding of the DNA double helix ahead of the replication fork as the DNA is opening up; it does so by causing temporary nicks in the DNA helix and then resealing it.
DNA pol I
Exonuclease activity removes RNA primer and replaces it with newly synthesized DNA.
DNA Ligase
Seals the gaps between the Okazaki fragments on the lagging strand to create one continuous DNA strand.
DNA pol II
Single-Stranded Binding Proteins
Bind to single-stranded DNA to prevent hydrogen bonding between DNA strands, reforming double-stranded DNA.
Topoisomerase IV
Introduces single-stranded break into concatenated chromosomes to release them from each other, and then reseals the DNA.
Translation/Protein Synthesis
The second part of gene expression, involves the decoding by a ribosome of an mRNA message into a polypeptide product.
Protein Sequence
Consists of 20 commonly occurring amino acids.
Codon
A triplet of nucleotides that makes up each amino acids within the mRNA.
Genetic Code
The relationship between an mRNA codon and its corresponding amino acid.
Degeneracy
The number of possible three-nucleotide combinations is greater than the number of amino acids and a given amino acid is encoded by more than one codon; this causing a redundancy in the genetic code.
Wobble Position
The third position in a codon.
Reading Frame
The way nucleotides in mRNA are grouped into codons.
Polyribosome
The complete structure containing an mRNA with multiple associated ribosomes.
Anticodon
A three-nucleotide sequence that bonds with an mRNA codon through complementary base pairing.
A (aminoacyl) Site
Binds incoming charged aminoacyl tRNAs.
P (peptidyl) Site
Binds charged tRNAs carrying amino acids that have formed peptide bonds with the growing polypeptide chain but have not yet dissociated from their corresponding tRNA.
E (exit) Site
Releases dissociated tRNAs so that they can be recharged with free amino acids.
Peptidyl Transferase
An RNA-based ribozyme that is integrated into the 50S ribosomal subunit; helps with the formation of each peptide bond during the elongation step of translation.
Structural Genes
Encode products that serve as cellular structures or enzymes.
Regulatory Genes
Encode products that regulate gene expression.
Regulatory Region
Includes the promotor and the region surrounding the promotor, to which transcription factors can bind.
Transcription Factors
Proteins encoded by regulatory genes.
Repressor
Transcription factor that suppresses transcription of a gene in response to an external stimulus by binding to a DNA sequence within the regulatory region called the operator.
Activator
A transcription factor that increases the transcription of a gene in response to an external stimulus by facilitating RNA polymerase binding to the promotor.
Inducer
A small molecule that either activates or represses transcription by interacting with a repressor or an activator.
Constitutively Expressed
Are transcribed and translated continuously to provide the cell with constant intermediate levels of the protein products.
Repressible Operons
Typically contain genes encoding enzymes required for a biosynthetic pathway.
Inducible Operons
Contain genes encoding enzymes in a pathway involved in the metabolism of a specific substrate like lactose.
Regulon
A group of operons all controlled simultaneously.
Alarmones
Small intercellular nucleotide derivatives; change which genes are expressed and stimulate the expression of specific stress-response genes.
Attenuation
Secondary stem-loop structures formed within the 5’ end of an mRNA being transcribed determine if transcription to complete the synthesis of the mRNA will occur and if this mRNA will be used for translation.
Mutation
A heritable change in the DNA sequence of an organism.
Point Mutation
Affects a single base and most commonly occurs when one base is substituted or replaced by another.
Insertion
A mutation resulting from the addition of one or more bases.
Deletion
A mutation resulting from the removal of one or more bases.
Silent Mutation
A change that has no effect on the protein’s structure.
Missense Mutation
Results in a different amino acid being incorporated into the resulting polypeptide.
Conditional Mutations
When the effects of missense mutations may be only apparent under certain environmental conditions.
Nonsense Mutation
Converts a codon encoding an amino acid (a sense codon) into a stop codon (a nonsense codon).
Frameshift Mutations
Cause by insertions or deletions of a number of nucleotides that are not a multiple of three.
