Microbiology-Chapter 8

Front 1

Genetics

Back 1

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

Front 2

Gene

Back 2

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

Front 3

Chromosome

Back 3

Structure containing DNA that physically carries hereditary information; the chromosomes contain the genes

Front 4

Genome

Back 4

All the genetic information in a cell

Front 5

Genomics

Back 5

The molecular study of genomes

Front 6

Genotype

Back 6

The genes of an organism (DNA)

Front 7

Phenotype

Back 7

Expression of the genes
(ex: hair color, eye color)

Front 8

DNA

Back 8

-Polymer of nucleotides: Adenine, Thymine, Cytosine, Guanine
-Double helix associated with proteins
-"Backbone" is deoxyribose-phosphate
-Strands are held together by hydrogen bonds between AT and CG
-Strands are antiparallel
(5' to 3' and 3' to 5')

Front 9

DNA Replication

Back 9

-Semiconservative
---1 parent strand (original) and 1 newly made strand (daughter strands have)

Front 10

DNA Synthesis

Back 10

-DNA is copied by DNA polymerase
---in the 5'-->3' direction
---initiated by an RNA primer
---leading strand is synthesized continuously
---lagging strand is synthesized discontinuously
---Okazaki fragments
---RNA primers are removed and Okazaki fragments joined by a DNA polymerase and DNA ligase

Front 11

DNA Synthesis

Back 11

-single strand binding protein
*keeps strands seperate
-primase
*builds primers
-ligase
*seals over the gaps

Front 12

Steps of DNA Replication

(ON TEST!!)

Back 12

1. Topoisomerase relaxes supercoiled DNA
2. Helicase unwinds the double helix by breaking hydrogen bonds between the base pairs
3. Destabilizing Enzymes (SSB) bind to the single strands to keep the strands seperated
4. Primase adds RNA primers to initiate DNA synthesis
5. DNA polymerase 3 binds at the RNA primers, DNA polymerase 1 removes primers and DNA polymerase 3 synthesizes new DNA in the 5' to 3' direction on both the leading and lagging strands
6. Fragments of DNA (Okazaki fragments on the lagging strand) are joined by the enzyme DNA ligase

Front 13

Information Transfer

(ON TEST!!!)

Back 13

Transcription- RNA is made from DNA code. The RNA has complementary bases to the DNA

**DNA--->RNA

Translation-RNA is used as a template to make protein Amino acids, protein building blocks are coded by the base pairs on the RNA

**RNA--->Protein

Front 14

Transcription

Back 14

-DNA is transcribed to make RNA (mRNA, tRNA, and rRNA)
-Transcription begins with RNA polymerase binds to the promoter sequence
-Transcription proceeds in the 5'--->3' direction
-Transcription stops when it reaches the terminator sequence

Front 15

RNA Processing in Eukaryotes

Back 15

-Occurs between transcription and translation
-INTRON: intervening sequence, removed by RNA splicing
-EXON: coding sequence, "stay"

Front 16

Translation

Back 16

-Protein is synthesized based on code in mRNA
-The mRNA nucleotides are arranged in 3 nucleotide units called codons. Codons do not overlap.
-CODON: Group of three nucleotides on mRNA that codes for an amino acid
-DEGENERATE CODE: Most amino acids specified by more than one codon

Front 17

The Genetic Code

Back 17

-64 sense codons on mRNA encode the 20 amino acids (redundancy)
**redundant: more than 1 codon codes for the same amino acid
-Translation of mRNA begins at the start codon: AUG
-Translation ends at nonsense codons:UAA, UAG, UGA
-tRNA carries the complementary anticodon

Front 18

3 Types of RNA

Back 18

1. messenger RNA (mRNA)
2. transfer RNA (tRNA)
3. ribosomal RNA (rRNA)

Front 19

messenger RNA
(mRNA)

Back 19

Carries DNA message through complementary copy: message is in triplets called codons

**product of transcription**

Front 20

transfer RNA
(tRNA)

Back 20

Secondary structure creates loops; bottom loop exposes a triplet of nucleotides called anticodon which designates specificity and complements mRNA; carries specific amino acids to ribosomes

**translation**

Front 21

ribosomal RNA
(rRNA)

Back 21

component of ribosomes where protein synthesis occurs

Front 22

Steps to Translation

Back 22

1. Translation of mRNA begins at the start codon: AUG
2. Translation ends at a STOP codon
3. The large and small ribosomal subunits and tRNA with UAC anticodon and corresponding methonine amino acid assemble at the AUG start codon
4. The first tRNA moves to the P site of the ribosome and the second tRNA with the next amino acid enters A site of the ribosome
5. The ribosome joins the two amino acids with a peptide bond
6. The first tRNA molecule leaves the ribosome and the second tRNA moves into P site while the third tRNA and its amino acid enters A site
7. The process proceeds down the mRNA and amino acid chain is formed
8. Translation ends when one of three nonsense (stop codons) UAA, UAG, UGA is reached and the ribosome subunits separate from the mRNA and release the polypeptide chain, tRNA

Front 23

Process of Translation

Back 23

Three phases:
1. initiation
2. elongation
3. termination

Front 24

Three Locations for tRNA

Back 24

1. P site
2. A site (arrival)
3. E site

Front 25

The Regulation of Bacterial Gene Expression

Back 25

-Constitutive genes are expressed at a fixed rate
-Other genes are expressed only as needed
**Repressible genes

(normally on, can be turned off)
**Inducible genes

(normally off, can be turned on)
**Catabolite repression

Front 26

Inducible Operon: Lac Operon

Back 26

-Normally off, can be turned on
-Genes required for lactose metabolism in E. coli are inducible
-B-galactosidase breaks down lactose into glucose and galactose
-When no lactose is present in the media, E. coli do not make B-galactosidase
-When lactose is present in the media it is converted by the cell to allolactose
-Allolactose induces the transcription of B-galactosidase.
-SUMMARY: when lactose is present, allolactose is present which turns on B-galactosidase to process the lactose

Front 27

Lac Operon genes

Back 27

I- Gene for repressor protein
P- Promoter
O- Operator
lac Z- Gene for B-galactosidase
lac Y- Gene for B-galactosidase permease
lac A- Gene for B-galactosidase transacetylase

Front 28

Repressible Operon: Tryptophan Operon

Back 28

-Normally on, can be turned off
-Genes required for tryptophan synthesis are normally transcribed
-When excess tryptophan is present, it can act as a corepressor

**catabolic activating protein (positive regulation):
---glucose is high, CAMP is low, and CAP is not active, will not bind promoter, no transcription of operon
---glucose is low, CAMP is high, CAMP binds CAP, CAP is active, binds promoter, transcription of lac operon

Front 29

Mutation

Back 29

-A change in the genetic material
-Mutations may be neutral, beneficial, or harmful
-MUTAGEN: Agent that causes mutations
-SPONTANEOUS MUTATIONS: Occur in the absence of a mutagen

Front 30

Four Types of Mutations

Back 30

1. Base substitution (point mutation): Change in one base

2. Missense mutation: Result in change in amino acid

3. Nonsense mutation: Results in a change nonsense codon

4. Frameshift mutation: Insertion or deletion of one or more nucleotide pairs

Front 31

The Frequency of Mutation

Back 31

-Spontaneous mutation rate=1 in 10^9 replicated base pairs or 1 in 10^6 replicated genes

-Mutagens increase to 10^-5 or 10^-3 per replicated gene

Front 32

Radiation

Back 32

-Ionizing radiation: (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone

-UV radiation causes thymine dimers

Front 33

Repair

Back 33

-Photolyases separate thymine dimers

-Nucleotide excision repair

Front 34

Ames Test for Chemical Carcinogens

(POSSIBLE ESSAY QUESTION!!)

Back 34

-Salmonella (will not grow on media, lacking histidine)
**HIS- (requires histidine in media to grow)
**Back mutates to HIS+ (is able to make its own histidine and can grow on media lacking histidine)

Front 35

Genetic Transfer and Recombination

Back 35

Vertical gene transfer
-Occurs during reproduction between generations of cells
-parent cell-->daughter cell

Horizontal gene transfer
-The transfer of genes between cells of the same generation
-expression

Front 36

Genetic Recombination

Back 36

-Exchange of genes between two DNA molecules
**crossing over occurs when two chromosomes break and rejoin

Front 37

Genetic Recombination in Bacteria

Back 37

1. Conjugation
2. Transformation
3. Transduction

Front 38

Genetic Transformation

Back 38

Transformation: chromosomes fragments from a lysed cell are accepted by a recipient cell

*S. pneumonial with capsule
-->smooth colonies
(killed the mice)

*S. pneumonial without capsule
-->rough colonies

Front 39

Bacterial Conjugation

Back 39

-Conjugation: transfer of a plasmid or chromosomal fragment from a donor cell to a recipient cell via direct connection

---gram negative cell donor has a fertility plasmid (F plasmid, F' factor) that allows the synthesis of a conjugation (sex) pilus

---High frequency recombination: the donor's fertility plasmid has been integrated into the bacterial chromosome

Front 40

Transduction by a Bacteriophage

Back 40

Transduction: bacteriophage serves as a carrier of DNA from a donor cell to a recipient cell

*Generalized
*Specialized

Front 41

Plasmids

Back 41

-Plasmids: small, self-replicating, circular DNA

**Conjugative plasmid: carries genes for sex pili and transfer of the plasmid

**Dissimulation plasmids: encode enzymes for catabolism of unusual compounds

**R factors: encode antibiotic resistance

Front 42

Transposons

Back 42

-Segments of DNA that can move from one region of DNA to another
-Contain insertion sequences for cutting and resealing DNA (transposase)
-Complex transposons carry other genes

Front 43

Genes and Evolution

Back 43

-Mutations and recombination provide diversity
-Fittest organisms for an environment are selected by natural selection

Front 44

DNA Gyrase

Back 44

Relaxes supercoiling ahead of the replication fork

Front 45

DNA Ligase

Back 45

Makes covalent bonds to join DNA strands; joins Okazaki fragments and new segments in excision repair

Front 46

DNA Polymerase

Back 46

Synthesizes DNA; proofreads and repairs DNA

Front 47

Helicase

Back 47

Unwinds double-stranded DNA

Front 48

RNA Primase

Back 48

An RNA polymerase that makes RNA primers from a DNA template

Front 49

Topoisomerase

Back 49

Relaxes supercoiling ahead of replication fork; separates DNA circles at the end of DNA replication

Front 50

Catabolic Activating Protein: positive regulation

(ON TEST!!!)

Back 50

-Glucose is high, CAMP is low, and CAP is not active, will not bind promoter, no transcription of operon
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-Glucose is low, CAMP is high, CAMP binds CAP, CAP is active, binds promoter, transcription of lac operon