Microbio Chapter 8

Genetics

The study of genes how they carry information how information is expressed and how genes are replicated.

Chromosome

A structure containing DNA that physically carries hereditary information and contains genes.

Gene

A segment of DNA that encodes a functional product usually a protein.

Genome

All the genetic information in a cell.

Genetic code

A set of rules that determines how a nucleotide sequence is converted to an amino acid sequence.

Central dogma

DNA is used to make mRNA which is used to make protein.

Genotype

The genetic makeup of an organism.

Phenotype

The expression of an organism's genes.

Bacterial chromosome

Bacteria usually have a single circular chromosome made of DNA and associated proteins.

Vertical gene transfer

The flow of genetic information from one generation to the next.

DNA double helix

The twisted structure formed by two strands of DNA.

DNA backbone

A backbone consisting of deoxyribose sugar and phosphate.

DNA base pairing

A pairs with T and C pairs with G using hydrogen bonds.

Antiparallel strands

DNA strands run in opposite directions.

DNA genetic instructions

The order of nitrogen-containing bases forms the genetic instructions of an organism.

DNA replication

The process of producing a new DNA strand using an existing strand as a template.

DNA template strand

A DNA strand that serves as a template for producing a complementary strand.

Topoisomerase

An enzyme that relaxes DNA strands during replication.

Gyrase

An enzyme that relaxes DNA strands during DNA replication.

Helicase

An enzyme that separates the two DNA strands.

Replication fork

The location where the DNA double helix is separated during replication.

DNA polymerase

An enzyme that adds nucleotides to a growing DNA strand.

RNA primer

A short RNA sequence that initiates DNA replication.

Leading strand

The DNA strand synthesized continuously during replication.

Lagging strand

The DNA strand synthesized discontinuously during replication.

Okazaki fragments

Short DNA fragments produced during synthesis of the lagging strand.

DNA ligase

An enzyme that joins Okazaki fragments together.

Bidirectional replication

DNA replication that proceeds in two directions from the origin.

DNA proofreading

The proofreading ability of DNA polymerase that helps make replication highly accurate.

RNA

Ribonucleic acid that is single-stranded and contains ribose sugar and uracil.

RNA sugar

RNA contains the five-carbon sugar ribose.

RNA base

RNA contains uracil instead of thymine.

rRNA

Ribosomal RNA that is an integral part of ribosomes.

tRNA

Transfer RNA that transports amino acids during protein synthesis.

mRNA

Messenger RNA that carries coded information from DNA to ribosomes.

Transcription

The synthesis of a complementary mRNA strand from a DNA template.

RNA polymerase

An enzyme that produces RNA during transcription.

Promoter

A DNA sequence where RNA polymerase begins transcription.

Terminator

A DNA sequence where transcription stops.

Translation

The process in which mRNA is translated into the language of proteins.

Codon

A group of three mRNA nucleotides that codes for a particular amino acid.

Sense codons

The 61 codons that encode the 20 amino acids.

Start codon

The codon AUG that signals the beginning of translation.

Nonsense codons

The stop codons UAA UAG and UGA that end translation.

Anticodon

A sequence on tRNA that base-pairs with an mRNA codon.

Peptide bond

A bond that joins amino acids together during protein synthesis.

Bacterial transcription and translation

In bacteria translation can begin before transcription is complete.

Eukaryotic transcription

Transcription occurs in the nucleus of eukaryotic cells.

Eukaryotic translation

Translation occurs in the cytoplasm of eukaryotic cells.

Exons

Regions of DNA that code for proteins.

Introns

Regions of DNA that do not code for proteins.

snRNPs

Small nuclear ribonucleoproteins that remove introns and splice exons together.

Gene expression

The process by which genetic information is used to produce functional products.

Constitutive genes

Genes that are expressed at a fixed rate.

Inducible genes

Genes that are expressed only when needed and are normally off.

Repressible genes

Genes that are normally expressed but can be turned off.

Repression

A process that inhibits gene expression and decreases enzyme synthesis.

Repressor

A protein that blocks transcription.

Induction

A process that turns on gene expression.

Inducer

A molecule that initiates gene expression in an inducible system.

Promoter in an operon

A DNA segment where RNA polymerase initiates transcription of structural genes.

Operator

A DNA segment that controls transcription of structural genes.

Operon

A set of operator and promoter sites plus the structural genes they control.

Inducible operon

An operon whose structural genes are not transcribed unless an inducer is present.

Lac operon

An inducible operon involved in lactose metabolism.

Allolactose

A metabolite of lactose that acts as an inducer of the lac operon.

Lac operon without lactose

The repressor binds to the operator and prevents transcription.

Lac operon with lactose

Allolactose binds to the repressor preventing it from binding to the operator so transcription occurs.

Repressible operon

An operon whose structural genes are transcribed until they are turned off.

Corepressor

A molecule that binds to and activates a repressor.

Tryptophan as a corepressor

Excess tryptophan binds to and activates the repressor which stops tryptophan synthesis.

Epigenetic control

Control of gene expression through changes that can be passed to offspring cells without permanently changing DNA.

DNA methylation

Methylation of nucleotides that turns genes off.

Methylated genes

Genes that are turned off by nucleotide methylation and can be passed to offspring cells.

Riboswitch

A part of an mRNA molecule that binds to a substrate and changes the mRNA structure.

Riboswitch function

A riboswitch can cause translation to be initiated or stopped.

microRNA

Small RNA molecules that base-pair with mRNA and can prevent protein production.

microRNA gene regulation

microRNA makes mRNA double-stranded which causes the RNA to be enzymatically destroyed.

Mutation

A permanent change in the base sequence of DNA.

Effects of mutations

Mutations may be neutral beneficial or harmful.

Mutagen

An agent that causes mutations.

Spontaneous mutation

A mutation that occurs in the absence of a mutagen.

Base substitution

A point mutation involving a change in one DNA base.

Point mutation

A mutation involving a change in one DNA base.

Missense mutation

A base substitution that results in a change in an amino acid.

Nonsense mutation

A base substitution that results in a nonsense stop codon.

Frameshift mutation

A mutation caused by insertion or deletion of one or more nucleotide pairs that shifts the reading frame.

Chemical mutagen

A chemical agent that causes mutations.

Nitrous acid

A chemical mutagen that causes adenine to bind with cytosine instead of thymine.

Ionizing radiation

X-rays and gamma rays that form ions which can oxidize nucleotides and break the DNA backbone.

UV radiation

Radiation that can cause thymine dimers.

Thymine dimer

A DNA damage involving two adjacent thymine bases bonding together.

Photolyase

An enzyme that separates thymine dimers.

Nucleotide excision repair

A repair process in which enzymes remove incorrect bases and replace them with correct bases.

Genetic recombination

The exchange of genes between two DNA molecules that creates genetic diversity.

Horizontal gene transfer

The transfer of genes between cells of the same generation.

Mobile genetic elements

Genetic elements that can move from one chromosome to another or from one cell to another.

Plasmid

A self-replicating circular piece of DNA.

Plasmid size

Plasmids are about 1 to 5 percent the size of a bacterial chromosome.

Pathogenicity plasmids

Plasmids that often code for proteins that enhance bacterial pathogenicity.