Microbial Genetics Flashcards by Kimberly Jayme

basic unit of heredity
segments of DNA (RNA for some
viruses) that code for functional
products (proteins, RNAs)
DNA sequences that are required to
produce a polypeptide chain

Gene

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regions of DNA that contain the actual
instructions for the sequence of amino
acids in a protein (coding regions)
stretches of DNA sequence that help
regulate expression of gene (noncoding
regions)

Polypeptide chain

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macromolecule composed of repeating units called nucleotides

DNA

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nitrogenous base + deoxyribose + phosphate group ( the 3 components)

Nucleotide

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string of nucleotides
joined together by
phosphodiester linkages
macromolecule
deoxyribonucleoside 5-
monophosphate

Molecular Structure of DNA: Primary Structure

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three-dimensional
configuration of DNA
double helical structure
two polynucleotide
strands wound around
each other

Molecular Structure of DNA: Secondary Structure

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DNA Model: two long polynucleotide chains are coiled around a central
axis, forming a right-handed _____________

double helix

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Two chains of DNA Model are _____________

antiparallel (C-5’-to-C-3’ orientation runs in opposite directions)

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base of both chains are paired to one another as the result of the formation of hydrogen bonds

specificity and complementarity (A=T, C=G)

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Molecular forces that hold two strands together:

▪ Hydrogen bond
▪ hydrophobic interactions between stacked base pairs

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▪ found in cytoplasm
▪ circular chromosome
▪ single chromosome plus plasmid
▪ made up of only DNA
▪ copies its chromosomes and divides immediately

Prokaryotic Chromosome

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▪ found in nucleus
▪ linear chromosome
▪ many chromosomes, usually 10-50 chromosomes in somatic cells
▪ made up of DNA, histone proteins
▪ copies its chromosome grows cell and then divides equally through mitosis

Eukaryotic Chromosome

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Bacteria have a ___________________ consisting of a single circular molecule of DNA with associated proteins

single circular chromosome

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The chromosome is _________________________ and attached at one or several points to the plasma membrane.

Looped and folded

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The chromosome takes up only about 10% of the cell’s volume because the ________________

DNA is twisted, or supercoiled

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Model of E. coli Chromosome

Folded = coiled
Nicked = single strand

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Chromosome length of E.coli

~1 mm

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individual unit of replication

replicon

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where replication starts and continues until entire replicon has been replicated

origin of replication

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loop where replication occurs

replication bubble

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point of unwinding, where two single nucleotide
strands separate from the double-stranded DNA helix

replication fork

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DNA Replication Takes Place in a
_________________ Manner

Semiconservative

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❑ intragenic regions
❑ intervening
nucleotide
sequences that do
not directly code for
proteins and are
removed in pre-mRNA

Introns

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portions of gene that codes for amino acids

Exons

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Three staged of Prokaryotic Translation

Initiation, Elongation, Termination

binding of ribosome (containing rRNAs and proteins) and aminoacyl tRNA to mRNA.

Initiation

addition of one aa at a time to the growing polypeptide chain

Elongation

release of finished polypeptide from tRNA and dissociation of ribosome from mRNA

Termination

determines how the nucleotide sequence specifies the amino acid sequence of a protein

Genetic code

three nucleotides encode each amino acid in a protein

triplet code

❑ basic unit of the genetic code ❑ set of bases that encode a single amino acid ❑ contains three nucleotides

codon

three stop codons:

UAA, UAG, UGA

is written in a linear form, using the ribonucleotide bases that compose mRNA molecules as “letters”

Genetic code

is derived from the complementary nucleotide bases in DNA.

Ribonucleotide sequence

prokaryotic mRNA can be _____________

polycistronic

can produce more than one protein

polycistronic

eukaryotic mRNA are usually _________________

monocistronic

each can encode only a single polypeptide

monocistronic

Pre Transcriptional Controls

Repression and Induction

❑ Two genetic control mechanisms that regulate the transcription of mRNA, and consequently, the synthesis of enzymes from them. ❑ These mechanisms control the formation and amounts of enzymes in the cell, not the activities of the enzymes.

Repression and Induction

The regulatory mechanism that inhibits gene expression and decreases the synthesis of enzymes.

Repression

the process that turns on the transcription of a gene or genes

Induction

a substance that initiates transcription of a gene

Inducer

enzymes that are synthesized in the presence of inducers

Inducible enzymes

Example of an inducible system:

genes required for lactose metabolism in E. coli

True or False: The default position of a repressible gene is off.

False: on

True or False: The default position of an inducible gene is on.

False: off

the bacterial cells can produce a large quantity of the enzyme when ______________ is added to the medium

lactose

the presence of ___________ indirectly induces the cells to synthesize more enzyme

lactose

Pre-Transcriptional Controls

Positive and Negative controls

❑ processes that stimulate gene expression ❑ regulatory protein is an activator

Positive control

❑ processes that inhibit gene expression ❑ regulatory protein is a repressor

Negative control

Formulated the operon control of gene expression by induction and repression:

Francois Jacob and Jacques Monod (1960s)

The model shows induction of the enzymes of lactose catabolism in E. coli

Operon model

❑ bacterial genes that have related functions are clustered together ❑ bacterial genes that have related functions are under the control of a single promoter ❑ often transcribed together into a single mRNA

OPERON

❑ group of bacterial structural genes that are transcribed together (with their promoter and additional sequences that control transcription) ➢ basic unit of transcriptional control in bacteria

OPERON

Two relatively short segments of DNA in lac operon:

Promoter, Operator

is the segment where RNA polymerase initiates transcription

Promoter

acts as a go or stop signal for transcription of the structural genes

Operator

the combination of the three lac structural genes and the adjoining control regions is called _______________

LAC OPERON

OPERON STRUCTURE:

Structural genes, Promoter, Regulator Gene, Regulator protein

transcribed into a single mRNA, which is translated to produce enzymes (transcription is under the control of a promoter)

structural genes

where RNA polymerase binds to and moves downstream, transcribing the structural genes

promoter

helps control transcription of the structural genes of the operon (not part of the operon, has its own promoter and is transcribed into short mRNA and translated into small protein or regulator protein)

regulator gene

bind to a region of DNA operator and affect whether transcription can take place

regulator protein

The Operon Model of Gene Expression

LAC PERMEASE, TRANSACETYLASE, STRUCTURAL GENES

is involved in the transport of lactose into the cell

LAC PERMEASE

metabolizes certain disaccharides other than lactose

TRANSACETYLASE

the genes, which determine the structures of proteins

STRUCTURAL GENES

LAC Operon Enzymes:

Permease, β-galactosidase, Thiogalactoside transacetylase

❑ actively transports lactose into the cell ❑ encoded by lacZ gene

Permease

❑ breaks lactose into glucose and galactose; can convert lactose to allolactose (has a role in regulating lactose metabolism) ❑ encoded by lacY gene

β-galactosidase

❑ unknown function ❑ encoded by lacA gene

thiogalactoside transacetylase

❑ regulator gene ❑ transcribed into a short mRNA and translated into a repressor/inhibitor ❑ consist of four identical polypeptides ❑ has two binding sites ❑ one site binds to allolactose ❑ other site binds to DNA

lacI

a regulatory gene that encodes a repressor protein that switches inducible and repressible operons on or off

I gene

true or false: the lac operon is an inducible operon

True

true or false: in the presence of lactose, the repressor binds to the operator site, thus preventing transcription

False: absence of lactose

true or false: If lactose is present, the repressor binds to a metabolite of lactose instead of to the operator, and lactose-digesting enzymes are transcribed.

true

❑ those in which transcription is normally off (not taking place) ❑ something must happen to induce transcription or turn it on

inducible operons

❑ those in which transcription is normally on (taking place) ❑ something must happen to repress transcription or turn it off

repressible operons

When excess tryptophan is present, the tryptophan acts as a ________________ binding to the repressor protein. The repressor protein can now bind to the operator, stopping further tryptophan synthesis.

Corepressor

negative repressible operon

TRP Operon

negative repressible operon

TRP Operon

a substance derived from ATP that serves as a cellular alarm signal.

cAMP

Enzymes that metabolize glucose are constitutive, and cells grow at their maximal rate with ____________ as their carbon source because they can use it most efficiently.

glucose

transcription of the lac operon requires both the presence of ___________ and the absence of _____________

lactose, glucose

transcription of the lac operon requires both the presence of ___________ and the absence of _____________

lactose, glucose

is an example of an alarmone, a chemical alarm signal that promotes a cell’s response to environmental or nutritional stress. (The stress is the lack of glucose)

Cyclic AMP

inhibition of the metabolism of alternative carbon sources by glucose is termed

catabolite repression or the glucose effect

Eukaryotic and bacterial cells can turn genes off by ______________ certain nucleotides—that is, by adding a methyl group 1-CH3 2.

methylating

Microbial Genetics Flashcards

(90 cards)