Microbiology Exam 3

Genetics

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

Chromosome

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

23 chromosomes in humans

* 22 somatic
* 1 sex chromosome (x,y)

genome

all the genetic information in a cell

we al have a different ___

DNA fingerprint

genomics

the molecular study of GENOMES

genotype

the genes of an organism (do not see)

phenotype

expression of the genes (what we see)

* expression of genotype

gene

a sequence of nucleotides in DNA that codes for a __functional product__ (hair color, eye color, etc.)

alteration of bacterial genes and gene expression

* cause of disease: Vibrio Cholerae → secretes enterotoxin → controlled by genes → change in gene can change the stability of disease
* prevent disease treatment
* manipulated for human benefit: insulin produced into E. coli, E. coli now produces insulin

genetic code

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

Central dogma chain of events

DNA → mRNA → Protein → function

transcription is going from

DNA → RNA

Translation is going from

RNA → protein

DNA stands for

Deoxyribonucleic acid

Components of DNA

* deoxyribose = sugar (missing O2)
* phosphate
* nitrogenous bases = adenine, guanine, thymine, cytosine

nucleotide is composed of

sugar + phosphate + base

nucleoside is composed of

sugar + base

DNA Polymerase functions

* copies DNA strand
* proofreads

What relaxes the strands during DNA replication

topoisomerase and gyrase

what separates the stands during DNA replication

helicase

semiconservative reproduction

one strand from parents making a new one

replication ALWAYS happens in what direction

5’ → 3’

steps of DNA replication

1. helicase unwinds the parental double helix (creating replication fork)
2. proteins stabilize the DNA strand
3. leading strand in synthesized CONTINUOUSLY by DNA polymerase
4. lagging strand is synthesized DISCONTINUOUSLY (creating Okazaki fragments)
5. DNA ligase joins the discontinuous fragments of the lagging strand

DNA function

* contains genetic profile of cell (DNA fingerprint)
* undergoes transcription into RNA

RNA strands for

Ribonucleic acid

components of RNA

* ribose = sugar (contains O2)
* phosphate
* nitrogenous bases = guanine, cytosine, adenine, uracil

Differences btw DNA and RNA

DNA

* double helix
* contains thymine
* two strands running antiparallel

RNA

* single stranded nucleotide
* 5 carbon ribose sugar
* contains uracil not thymine

function of RNA

performs protein synthesis

Types of RNA

* ribosomal RNA (rRNA)
* transfer RNA (tRNA)
* messenger RNA (mRNA)

ribosomal RNA (rRNA)

integral part of ribosomes

transfer RNA (tRNA)

transports amino acids during protein synthesis

messenger RNA (mRNA)

carries coded information from DNA to ribosomes

TRANSCRIPTION process steps

1. initiation
2. elongation
3. termination

when the end product is DNA, what is the. most important enzyme

DNA polymerase

when the end product is RNA what is the most important enzyme

RNA polymerase

TRANSCRIPTION starts at the ___ and ends at the

promoter; terminator

process of TRANSCRIPTION

1. transcription begins at the promoter
2. RNA polymerase binds to the promoter and DNA unwinds
3. RNA is synthesized by complementary base pairing of free nucleotides with the nucleotide bases in the template strand of DNA
4. the site of synthesis moves along DNA
5. transcription reaches the terminator

codon

groups of THREE mRNA nucleotides that code for a particular amino acid (ex: AUG)

components involved in TRANSLATION

* ribosome
* mRNA
* tRNA
* amino acid

ribosome subunits for prokaryotes

50S and 30S = 70S

ribosome subunits for eukaryotes

60S and 40S = 80S

TRANSLATION starts at the ___ and ends at the

start codon; stop codon or nonsense codon

what is the start codon

AUG

mutation

a change in genotype which may or may not affect the phenotype

mutagen

agent that causes mutations

spontaneous mutation

* occur naturally
* happen one in a billion times (10^9)

Induced mutation

induced by a chemical or physical agent

silent mutation

changes in genotype, but not phenotype

types of mutations

* base substitution mutations
* frameshift mutations

base substitution mutations include

* silent mutations
* missense mutations
* nonsense mutations

missense mutation

changes an amino acid

nonsense mutation

stop/nonsense codon; results in a completely different sequence

base substitution mutation (point mutation)

* change in ONE BASE
* the most common type

frameshift mutations include

* frameshift insertion of one or more nucleotide pairs
* frameshift deletion of one or more nucleotide pairs

spontaneous mutation rate

* 1 in 10^9 in replicated base pairs
* 1 in 10^6 in replicated genes

nitrous acid

* causes adenine to bind with cytosine instead of thymine
* example of chemical mutagen

Double mutation (DM)

double mutation in specific genes in a single cell that initiate cancer

inducers

start mutations

promoters

make mutations multiply

chemicals in cigarettes

* cyanhydric acid
* ammoniac
* urethane
* toluene
* arsenic
* DDT

induced mutations can be caused by

mutagens: chemicals, radiation, or physical

UV light exposure at ________ leads to the formation of thymine dimers

260 nm

endonuclease

cut thymine dimers

exonuclease

remove thymine dimers

photolyases

separates thymine dimers

final effect of UV light exposure depends on

* presence of barriers
* time exposed

nucleotide excision repair

1. thymine attaches to adjacent thymine
2. endonuclease cuts the DNA
3. exonuclease removes the DNA
4. DNA polymerase fills the gap
5. ligase seals the gap

genetic recombination

exchange of genes between two DNA molecules; creates genetic diversity

crossing over

two chromosomes break and rejoin, resulting in the insertion of foreign DNA to the chromosome

vertical gene transfer

transfer of genes from an organism to its offspring; from one generation to the next

horizontal gene transfer

transfer of genes between cells of the same generation

expression and recombination are examples of

horizontal gene transfer

the ONLY example of vertical gene transfer is

replication

types of genetic transfer

* transformation
* conjugation
* transduction

transformation

transfer of genetic information between DEAD (donor) cells and LIVING (recipient) cells as naked DNA in solution

conjugation

* the transfer of PLASMIDS
* transfers DNA horizontally

2 requirements of conjugation

* cell to cell contact with pilli
* cells must be of opposite mating types

conjugation in bacteria

* donor cells carry the plasmid (F factor) and are called F+ cells
* Hfr cells contain the F factor on the chromosome

transduction

transferring genetic material between cells using bacteriophage

2 types of transduction

* generalized
* specialized

generalized transduction

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

specialized transduction

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

in generalized transduction

ANY PEICE of chromosomal or plasmid DNA is packaged at random into the viral capsid during LYTIC lifecycle

in specialized transduction

ONLY pieces adjacent and attached to phage dNA are packaged into the viral capsid during LYSOGENIC cycle

plasmids are

* self replicating
* circular
* made of DNA

conjunctive plasmid

carries genes for sex pili and transfer of the plasmid

dissimilation plasmids

encode enzymes for the catabolism of unusual compounds

catabolism

breaking large molecules into small molecules which RELEASES energy

resistance factors (R factors)

encode antibiotic resistance

transposons

segments of DNA that can move from one region of DNA to another - jumping pieces of DNA

insertion sequences

code for transposase that cuts and reseals DNA

mutations and recombination create

cell diversity

diversity is the raw material for

evolution

natural selection

acts on populations of organisms to ensure the survival of organisms FIT for a particular environment

True or False: The is NO selective toxic medications

True

Selective toxicity

selectively finding and destroying pathogens WITHOUT damaging the host

chemotherapy

the use of CHEMICALS to treat a disease

* chemotherapy is NOT only cancer related; its most medications (ex: ibuprofen)

antibiotic

a substance produced by a microbe that, in small amounts, inhibits another microbe

* ex: penicillin

antimicrobial drugs

synthetic substances that interfere with the growth of microbes