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Microbiology > Microbial genetics > Flashcards

Microbial genetics Flashcards

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Biology 101 flashcards
1
Q

Genetics

A

The science of heredity, study of genes, how they caryy information, how information is expressed, and how genes are replicated

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2
Q

Chromosomes

A

Structures containing DNA that physically carry hereditary information; the chromosomes contain genes

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3
Q

Genes

A

Segments of DNA that encode functional products, usually proteins

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4
Q

Genome

A

All genetic information in a cell

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5
Q

Genetic code

A

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

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6
Q

Central Dogma

A

Describes the flow of genetic information in cells from DNA to messenger RNA (mRNA) to protein. It states that genes specify the sequence of mRNA molecules, which in turn specify the sequence of proteins

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7
Q

Genotype

A

The genetic makeup of an organism

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8
Q

Phenotype

A

Expression of the genes

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9
Q

Describe the structure of bacterial DNA

A

Usually a singular circular chromosome made of DNA and associated proteins- short tandem repeats (STRs) repeating sequencing of noncoding DNA

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10
Q

Vertical gene transfer

A

Flow of genetic information from one generation to the next

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11
Q

Horizontal gene transfer

A

transfer of genes between cells of the same generation–Transformation–Conjugation–Transduction

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12
Q

Describe the process of DNA replication

A

One strand serves as a template for the production of a second strand

  • Topoisomerase and gyrase- relax the strands
  • Helicase- separates the strands-replication fork is created
  • DNA polymerase adds nucleotides in the 5’ to 3’ direction, initiated by a RNA primer (made by primase)
  • DNA polymerase removes RNA primers; okazaki fragments are joined by the DNA polymerase and DNA ligase
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13
Q

DNA replication in leading strand

A

Synthesized continuously from 5’ to 3’

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14
Q

DNA replication in lagging strand

A

Synthesized discontinuously, creating okazaki fragments

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15
Q

Explain the bidirectionality and proofreading aspects of DNA replication

A

Most bacterial DNA replication is bidirectional; each offspring cell receives one copy of the DNA molecule; replication is highly accurate due to proofreading capability of DNA polymerase

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16
Q

What is the role of topoisomerase and gyrase in DNA replication?

A

Relax the strands

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17
Q

What is the role of Helicase in DNA replication?

A

Separates the strands creating the replication fork

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18
Q

What is the role of DNA polymerase in DNA replication?

A

Adds nucleotides in 5’ to 3’ direction starting at the RNA primers and joins okazaki fragments with the help of DNA ligase

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19
Q

What is the role of primase in DNA replication?

A

Making RNA primers

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20
Q

Ribosomal RNA (rRNA)

A

Integral part of ribosomes

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21
Q

Transfer RNA (tRNA)

A

Transports amino acids during protein synthesis

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22
Q

Messenger RNA (mRNA)

A

Carries coded information from DNA to ribosomes

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23
Q

Describe the process of Transcription in prokaryotes

A

Synthesis of a complementary mRNA strand from a DNA template

  • RNA polymerase binds to the promoter sequence on DNA (marks beginning of a gene)
  • Proceeds in 5’ to 3’ direction, only one of the two DNA strands is transcribed
  • Stops when it reaches the terminator sequence on DNA
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24
Q

Codon

A

Groups of three mRNA nucleotides that code for a particular amino acid (3 nucleotides=1 amino acid)

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25
Q

What is a sense codon and how many are there?

A

Sense codons code for amino acids; there are 61 sense codons that code for 20 amino acids

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26
Q

What is an antisense codon or nonsense codon and how many are there?

A

Nonsense codons indicate a “stop”, ending the translation process; there are 3 nonsense codons UAA, UAG, UGA

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27
Q

What is meant by degeneracy of the genetic code?

A

Each amino acid is coded by several codons

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28
Q

What is the “start codon” for all mRNA?

A

AUG

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29
Q

Describe the process of translation

A
  1. Begins at the start codon AUG; ends at nonsense codon UAG, UAA, UGA
  2. Codons of mRNA are read sequentially 3 at a time
  3. tRNA molecules transport the required amino acids to the ribosome (tRNA molecules also have an anticodon that base pairs with the codon) P site is the first site
  4. Amino acids are joined by peptide bonds (2nd codon of mRNA pairs with a tRNA carrying the 2nd amino acid at the A site
  5. The ribosome moves along the mRNA until the 2nd tRNA is in the P site; The next codon to be translated is brought to the A site, the first tRNA now occupies the E site
  6. The 2nd amino acid joins the 3rd by another peptide bond, and the 1st tRNA is released from the E site
  7. The ribosome continues to move along the mRNA, and new amino acids are added to the polypeptide chain until the ribosome reaches a stop codon and the polypeptide is released
  8. The last tRNA is released and the ribosome comes apart; The new polypeptide=new protein
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30
Q

How is bacterial translation different?

A

In bacteria, translation can begin before transcription is complete because DNA and ribosomes are all in same compartment (polyribosomes-a cluster of ribosomes linked together by a molecule of messenger RNA and forming the site of protein synthesis.); The first amino acid for prokaryotes is formyl-methionine (f-met)

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31
Q

Transcription in eukaryotes

A

Transcription occurs in the nucleus whereas translation occurs in the cytoplasm.
-Exons/ Introns/ SnRNPs

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32
Q

Exon

A

regions of DNA that code for proteins

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33
Q

Intron

A

Regions of DNA that do not code for proteins

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34
Q

Small nuclear ribonucleoproteins (snRNPs)

A

Remove introns and splice exons together

35
Q

Constitutive genes

A

Expressed at a fixed rate

36
Q

What genes are expressed only as needed

A

Inducible genes, Repressible genes; catabolite repression

37
Q

Repression

A

Inhibits gene expression and decreases enzyme synthesis

  • Mediated by repressors
  • Default position of repressible genes is “on”
38
Q

Repressors

A

Proteins that block transcription

39
Q

Induction

A

Turns on gene expression

  • Initiated by an inducer
  • Default position of an inducible gene is “off”
40
Q

The operon model of gene expression

A

Promoter-Operator-Structural genes = operon

41
Q

Promoter

A

Segment of DNA where RNA polymerase initiates transcription of structural genes

42
Q

Operator

A

Segment of DNA that controls transcription of structural genes (repressor or inducer bind here)

43
Q

Where do the repressor or inducer bind?

A

Operator

44
Q

Operon

A

Set of operator and promoter sites and the structural genes they control

45
Q

Inducible operon

A

Structural genes are not transcribed unless an inducer is present

  • No lactose=repressor binds to operator, preventing transcription (blocks RNA polymerase)
  • Lactose=lactose (inducer) binds repressor; repressor can’t bind to operator and transcription occurs
46
Q

Repressible operons

A

Structural genes are transcribed until they are turned off
-Excessive tryptophan is a corepressor; binds and activates the repressor to bind to the operator, stopping tryptophan synthesis

47
Q

Catabolite repression

A

Inhibits cells from using carbon sources other than glucose

  • cAMP builds up in a cell when glucose is not available
  • cAMP binds to the ‘lac’ promoter, initiating transcription and allowing the cell to use lactose
48
Q

Epigentic control (eukaryotes)

A
  • Methylating nucleotides turn genes off (histones)
  • Methylated “off” genes can be passed to offspring cells
  • Not permanent
49
Q

microRNAs (miRNAs)

A

Base-pair with mRNA to make it double stranded, double stranded RNA is enzymatically destroyed, preventing production of a protein

50
Q

Mutation

A

A permanent change in the base sequence of DNA; may be neutral, beneficial, or harmful

51
Q

Mutagen

A

Agents that cause mutations

52
Q

Spontaneuous mutations

A

Occur in the absense of a mutagen (incorrect base pairing during DNA replication)

53
Q

Base substitution (point mutation)

A

Changes in one base in DNA

54
Q

Missense mutation

A

Base substitution results in change in an amino acid

-Silent=No change in amino acid

55
Q

Nonsense mutation

A

Base substitution results in a nonsense (stop) codon

56
Q

Frameshift mutation

A

Insertion of deletion of one or more nucleotide pairs; shifts the translational “reading frame”

57
Q

Chemical mutagens

A

Nitrous acid/ Nucleoside analog

58
Q

Nitrous acid

A

Causes adenine to bind with cytosine instead of thymine

59
Q

Nucleoside analog

A

Incorporates into DNA in place of a normal base; causes mistakes in base pairing

60
Q

Ionizing radiation (xrays/gamma rays)

A

Causes formation of highly reactive ions; Can oxidize nucleotides and break the deoxyribose-phophate backbone

61
Q

Nonionizing radiation (UV rays)

A

Causes thymine dimers

-Photolyases separate thymine dimers

62
Q

Nucleotide excision repair

A

Enzymes cut out incorrect bases and fill in correct bases

63
Q

Positive (direct) selection of mutants

A

Detects mutant cells because they grow or appear different than unmutated cells

64
Q

Negative (indirect) selection of mutants

A

Detects mutant cells that cannot grow or perform a certain function

65
Q

Auxotroph

A

Mutant that has a nutritional requirement absent in parent

66
Q

Replica plating

A
  1. Master plate with different colonies of different potential mutants
  2. Sterile velvet surface pressed down on master plate
  3. Stamp colonies from velvet surface onto new plates with different medias
  4. Plates are incubated and growth of each plate is compared
67
Q

Ames test

A

Expose histidine auxotroph mutant salmonella to mutagenic substances to measure the rate of reversal of the mutation
-indicates degree to which a substance is mutagenic

68
Q

Genetic recombination

A

Exchange of genes between two DNA molecules; creates genetic diversity

69
Q

Crossing over

A

Two chromosomes break and rejoin, resulting in the insertion of foreign DNA into the chromosome

70
Q

Transformation (horizontal gene transfer)

A

Genes transferred from one bacterium to another as “naked” DNA

  1. Recipient cell takes up donor DNA
  2. Donor DNA aligns with complementary bases
  3. Recombination occurs between donor DNA and recipient DNA
71
Q

Conjugation (horizontal gene transfer)

A

Plasmids transferred from one bacterium to another

  1. Requires cell-to-cell contact via sex pili
  2. Donor cells carry the plasmid (F factor) and are called F+ cells (F= fertility)
  3. HFR cells contain F factor on the chromosome
72
Q

Transduction

A

DNA is transferred from a donor cell to a recipient via a bacteriophage; generalized and specialized

73
Q

Generalized transduction

A

Random bacterial DNA is packaged inside a phage and transferred to a recipient cell

74
Q

Specialized transduction

A

Specific bacterial genes are packaged inside a phage and transferred to a recipient cell

75
Q

Describe Griffith’s experiment

A
  1. Living encapsulated bacteria injected into a mouse- mouse died
  2. Living non encapsulated bacteria injected into mouse- mouse remained healthy
  3. Heat-killed encapsulated bacteria injected into mouse- mouse remained healthy
  4. Living non encapsulated and heat-killed encapsulated bacteria injected into mouse-mouse died
    - It was one of the first experiments showing that bacteria can get DNA through a process called transformation. … Griffith was also able to get both live II-R and live III-S strains of S. pneumoniae from the blood of these dead mice.
76
Q

Plasmid

A

Self-replicating circular pieces of DNA
1-5% the size of a bacterial chromosome
often code for proteins that enhance the pathogenicity of bacterium

77
Q

Conjugative plasmid

A

Carries genes for sex pili and transfer of the plasmid

78
Q

Dissimilation plasmids

A

Encode enzymes for the catabolism of unusual compounds

79
Q

Resistance factors (R factors)

A

Encode antibiotic resistance

80
Q

Transposons

A

Segments of DNA that can move from one region of DNA to another
-Contain insertion sequences (IS) that code fro transposase that cuts and reseals DNA

81
Q

Complex transposons

A

Carry other genes *antibiotic resistance

82
Q

Genetic transformation in bacteria

A
  1. Start with DNA fragments from donor cell and a recipient cell
  2. Recipient takes up donor DNA
  3. Donor DNA aligns with complimentary bases
  4. Recombination occurs between donor DNA and recipient DNA
  5. End with degraded unrecombined DNA and a genetically transformed cell
83
Q

Conjugation in bacteria

A
  • Donor cells carry the plasmid (F factor) and are called F+ cells
  • Hfr cells contain the F factor on the chromosome
    1. Mating bridge is formed between donor and recipient cell
    2. F factor (plasmid) transferred to recipient cell
    3. Recombination between F factor and chromosome occurs at a specific site on each
    4. Insertion of F factor into chromosome
    5. Recipient cell is now HFR cell
  • When a Hfr donor passes a portion of its chromosome to a F- cell, a recombinant F- cell results
84
Q

Transduction in bacteria

A
  1. Phage infects the donor bacterial cell
  2. Phage DNA and proteins are made, and the bacterial chromosome is broken into pieces
  3. Occasionally during phage assembly, pieces of bacterial DNA are packaged in a phage capsid. Then the donor cell lyses and releases phage particles containing bacterial DNA
  4. A phage carrying bacterial DNA infects a new host cell, the recipient cell
  5. Recombination can occur, producing a recombinant cell with a genotype different from both the donor and recipient cells

Microbiology (7 decks)

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