Microbio CH 8-9

Gene

A sequence of nucleotides that codes for the production of a functional product, usually a protein

Genotype

The genetic code, the information found in the genes

Phenotype

The physical trait that results from the expression of a gene, when the product of the gene is made

Are genes always expressed?

no

What does genotype direct?

Phenotypic expression

What are the two processes involved in the central dogma?

Transcription and translation

What is the Central Dogma?

The flow of genetic information

The 4 Major Types of RNA synthesized from DNA

Primers, mRNA, tRNA, and rRNA

Messenger RNA (mRNA)

Contains the code for the order of amino acids in a protein

Transfer DNA (tRNA)

Carries amino acids to ribosomes

Ribosomal RNA (rRNA)

A structural component of the ribosomes

Transcription

Synthesis of mRNA from DNA, carried out by RNA polymerase, and only one strand of the double stranded DNA serves as a template

What direction is RNA synthesized in?

5’ to 3’ direction

Transcription makes _____ using ____ template

mRNA; DNA

What is the enzyme that carries out transcription?

RNA polymerase

What is the starting point for transcription initiation?

RNA polymerase binds promoter sequence, and the DNA double helix is opened up

Elongation stage of DNA transcription

DNA used as a template, complementary nucleotide is added and the double helix unwinds in short segments

Termination stage of DNA transcription

Transcription ends at the terminator

Is sigma factor required in all types of cells?

No

What is sigma factor? What does it do?

A protein subunit in bacteria, required for the recognition of the promoter

Does RNA polymerase require other factors during elongation?

Yes

In what direction is DNA template read in?

3’ to 5’ direction

In what direction is RNA synthesized in?

5’ to 3’ direction

RNA Polymerase compared to DNA polymerase

No need for helicase or primer, slower, uracil added, and poor proofreading

Where does transcription occur in eukaryotes?

In the nucleus

Does transcription in eukaryotes require a sigma factor?

No sigma factor, many transcription factors and elongation factors instead

Capping

Addition of G nucleotides at 5’ end

Polyadenylation

Addition of 200 adenine to 3’ end

Splicing

Removal of introns or intervening sequences from pre mRNA by ribozymes

How do DNA codes occur?

In triplets

A triple is..

Any sequence of three consecutive nucleotide bases in a strand

What is a codon?

Any sequence of three consecutive nucleotides that specifies an amino acid

Why is genetic code redundant?

Most amino acids are coded for by more than one codon

Translation makes _____ using ____ template

proteins; mRNA

Where does translation occur?

In ribosome

Is ribosome an enzyme or a ribozyme?

A ribozyme

What are ribosomes composed of?

rRNA and proteins

What is tRNA? What is its function?

Carrier of amino acids, contains an anticodon, and is the link between RNA codons and amino acids

What do ribosomes do in translation?

Brings together mRNA and charged-tRNAs during translation

The three sites of translation

The acceptor site, the peptide site, and the exit site

What is the acceptor site (A-site) in translation for?

For tRNA carrying an amino acid

What is the peptide site (P-site) in translation for?

For tRNA carrying a polypeptide

What is the exit site (E-site) in translation for?

For the empty tRNA

tRNA

The link between RNA codon and an amino acid

Does charging of tRNA require an enzyme?

Yes

The three stages of translation

Initiation, elongation, and termination

What happens in the initiation stage of translation?

AUG (start codon) recognized by initiator tRNA carrying formyl-methionine

What happens in the elongation stage of translation?

The ribosome moves along the mRNA strand, amino acids are joined to form a growing polypeptide, and the mRNA is read in the 5’ to 3’ direction

What happens in the termination stage in translation?

The ribosome reaches a stop codon on the mRNA

Are additional proteins factors and energy (GTP) required in translation?

Yes

What recognizes stop codons in the termination stage of translation?

Release factors, and polypeptide from final tRNA is released from ribosomes

What happens in the initiation stage of translation in eukaryotes?

Ribosomal subunit binds to 5’ guanine cap, not RBS

Can multiple ribosomes be translating the mRNA at the same time?

Yes

Which mRNA can code for several polypeptides?

Prokaryotic mRNA

Polycistronic

More than a single gene

Operon

Genes that are transcribed together from promoter

What is coupling of transcription and translation? In which type of cells does it occur?

Process where the synthesis of mRNA and its decoding into a protein by a ribosome occur at the same place and time, occuring in prokaryotic cells

Microbial Growth

An increase in the number of cells

How is microbial growth defined differently from growth in other organisms?

It is an increase in the number of cells, rather than in size

Requirements for microbial growth

Chemical and physical

Chemical requirements for growth

Carbon, nitrogen, and oxygen

In general, nutrients provide ______ and ______ for growth and survival

Energy; building blocks

What is the role of carbon?

Provides the backbone of all organic molecules

What is the role of oxygen?

Essential for obligate aerobes, deadly for obligate anaerobes

What is the role of nitrogen?

For protein and nucleic acid synthesis

Based on the energy source, organisms are either:

Phototrophs, whose energy source is light; Chemotrophs, whose energy source is chemical compounds

Based on the Carbon source, organisms are either:

Autotrophs, whose carbon source is CO2; Heterotrophs, whose Carbon source is organic compounds

In which group are medically important microbes? Why?

Chemoheterotrophs, because the human body has many organic molecules that provide an ideal environment to extract both the energy and carbon needed

Why is oxygen toxic for anaerobes?

Toxic forms of oxygen are highly reactive and excellent oxidizing agents, which resulting oxidation causes irreparable damage to cells

The Four Toxic Forms of Oxygen

Singlet oxygen, superoxide radicals, peroxide anion, and hydroxl radical OH

Hydroxyl radical OH

Most reactive, from ionizing radiation

Peroxide Anion

Formed during lipid breakdown and through reactions catalyzed by enzymes

What does Superoxide dismutase (SOD) do?

Protects, but absent in anaerobes

What does catalase do?

Converts hydrogen peroxide (2H2O2) into water (2H2O) and oxygen gas (O2)

What does peroxide do?

Converts hydrogen pyroxide (H2O2), without producing oxygen gas (O2)

Superoxide radicals

Byproduct of metabolism in the presence of O2

Singlet oxygen

High energy electrons from aerobic respiration

Effect of oxygen on growth in Obligate aerobes

Only aerobic growth; oxygen required

Effect of oxygen on growth in Facultative anaerobes

Both aerobic and anaerobic growth; greater in oxygen

Effect of oxygen on growth in Obligative anaerobes

Only anaerobic growth; ceases in oxygen

Effect of oxygen on growth in Aerotolerant anaerobes

Only anaerobic growth, but continues in presence of oxygen

Microaerophiles

Only aerobic growth; oxygen required in low concentrations

What does growth look like in obligate aerobes?

Growth occurs only where high concentration of oxygen have diffused

What does growth look like in facultative anaerobes?

Growth is best where most oxygen is present, but occurs throughout tube

What does growth look like in obligate anaerobes?

Growth occurs only where there is no oxygen

What does growth look like in aerotolerant anaerobes?

Growth occurs evenly; oxygen has no effect

What does growth look like in microaerophiles?

Growth occurs only where a low concentration of oxygen has diffused

Nitrogen fixation

Process that converts nitrogen gas (N2) into compounds like ammonia (NH3) or nitrates (NO3)

At the temperature extremes, how are membranes affected?

Too low temperature makes membranes rigid and fragile, while too high temperature makes membranes too fluid and leaky

Protein denaturation

Collapse of the cytoplasmic membrane; thermalysis

Membrane gelling

Transport processes so slow that growth cannot occur

Thermophile

Organism that grows best in high temperatures

Mesophile

Organism that grows best in moderate temperatures

How does temperature effect proteins?

Protein folding, and enzyme denaturation

What is the temperature “Danger Zone”?

Between 40 and 140 degrees farenheit

Psychrophile

Organism that grows best in permanently cold environments

Hyperthermophile

Organism that grows best in extremely hot environments

Which type of microbe based on temperatures for growth, cause diseases in humans?

Mesophiles

Neutrophile

Organisms that grow best in neutral pH environments

Acidophiles

Organisms that grow best in acidic environments