4- Chapter 4 & 5

Question 1

What is the difference between eukaryotes and prokaryotes in the flow of genetic information?

Answer 1

Eukaryotes- each gene is on a single mRNA
Replication and transcription occur in the nucleus
RNA must be moved outside nucleus for translation
Prokaryotes- multiple genes may be on one mRNA
Coupled transcription and translation occur producing proteins at a maximal rate
Some viruses violate central dogma

Question 2

What are the 3 types of DNA packing?

Answer 2

1. Relaxed circular DNA
2. Relaxed nicked circular DNA
3. Supercoiled circular DNA
   Page 105 and 106 diagram

Question 3

What are plasmids?

Answer 3

Circular or linear double stranded DNA molecules that replicate separately from the chromosome and are typically much smaller than chromosome

Question 4

What direction is the leading strand in DNA replication and what direction is the lagging?

Answer 4

Leading- 5’ -> 3’
Lagging is same direction just follows behind the leading strand
Diagram on page 112 and 113
Lagging just works up the strand while leading works down

Question 5

What are intrinsic terminators and rho-dependant terminators?

Answer 5

Intrinsic- transcription is terminated without any additional factors
Rho-dependant- rho protein recognizes specific DNA (rna) sequences and causes a pause in the rna polymerase

Question 6

What does DNA helicase, primer, primase, and DNA ligase do?

Answer 6

Primer- in order to start a new chain, a nucleic acid molecule primer is added so DNA polymerase can attach
Primase- makes rna primer once DNA helix is first opened
Dna helicase- unwinds the double helix
DNA ligase- makes the very last phosphodiester bond
Seals nicks in DNA

Question 7

What is the unit of transcription?

Answer 7

Unit of chromosome bounded by sites where transcription of DNA to rna is initiated and terminated

Question 8

What is a polycistronic mRNA?

What is an operon?

Answer 8

Polycistronic mRNA- a mRNA encoding group of a cotranscribed genes
Operon- a group of related genes cotranscribed on a polycistronic mRNA
Allows for expression of multiple genes to be coordinated

Question 9

What are polysomes?

Answer 9

Highly expressed mRNAs can be translated by multiple ribosomes at the same time

Question 10

How does translation end?

Answer 10

When the ribosome reaches a “stop” codon

Release factors recognize the stop codon and cleave the polypeptide from the tRNA

Question 11

How is a stalled ribosome rescued?

Answer 11

Ribosomes become trapped if no stop codon remains at the end of a translated mRNA
TmRNA binds stalked ribosomes and allows completion of translation

Question 12

What are signal sequences?

Answer 12

Found on proteins requiring transport from cell
15-20 residues long
Found at beginning of protein molecule
Prevent protein from completely folding

Question 13

What is the tat system?

Answer 13

A transport system from a cells secretory system that export proteins that have folded in the cytoplasm

Question 14

What are the 4 types of one step secretion systems?

Answer 14

Type I- has a cytoplasmic membrane transporter coupled to an outer membrane pore by a membrane fusion protein
Type III- uses by pathogenic bacteria
Type IV- present in many bacteria and archaea
Type VI- gram negative bacteria can deliver diversity of proteins

Question 15

What is exponential growth?

Answer 15

Growth of microbial population in which cell numbers double within a specific time interval
Increases in cell number are initially slow but increases at a faster rate

Question 16

What is a batch culture?

Answer 16

A closed-system microbial culture of fixed volume
Growth conditions are constantly changing impossible to independently control both growth parameters
Lag phase
Exponential phase
Stationary phase
Death phase

Question 17

What is continuous culture?

What is chemostat?

Answer 17

Continuous- an open system microbial culture of fixed volume
Like a stream of nutrients and there’s a connected pool off to the side you use to study and it has constant volume
Chemostat- most common type of continuous culture device
Both growth rate and population density of culture can be controlled independently and simultaneously
Dilation rate- rate at which fresh medium is pumped in and spent medium is pumped out (controls growth rate)

Question 18

What is steady state chemostat culture?

Answer 18

Sensitive to the dilation rate and limiting nutrient concentration
Too high of a dilution rate will wash organism out
Too low dilution rate will kill cells from starvation
Graph on page 144

Question 19

What are the two methods for enumerating cells in liquid samples (counting)

Answer 19

1. Microscopic counts
   Unreliable results where you use the amount of cells in a section to estimate the amount
   Can’t tell if life or dead without stains
   Moving cells need to stop
2. Flow cytometer
   Uses laser beams, fluorescent dyes and electronics

Question 20

What are the two methods to perform plate counts?

Answer 20

Spread plate method- spread sample evenly over plate

Pour-plate method- sterile medium is added and mixed well with inoculum

Question 21

What is the great plate anomaly?

Answer 21

Direct microscopic counts of natural samples reveal far more organisms than those recoverable on plates
Because microscopic methods count dead cells, where as viable methods do not and different organisms has vastly different requirements for growth

Question 22

How is spectrophotometry used to count cells?

Answer 22

Turbidity measurements are indirect, rapid and useful measuring microbial growth
Turbidity of measured using a spectrophotometer
Quick and easy
Don’t require destruction or disturbance of sample

Question 23

What are extremophiles, psychrophiles, psychotolerants, thermophiles, and hyperthermophiles?

Answer 23

Extremophiles- can grow under very hot or very cold
Psychrophiles- organisms with cold temperature optima, inhabit permanently cold enviroments
Psychotolerant- organisms that can grow at 0C but have optima of 20C to 40C
More widely distributed in nature than psychrophiles
Thermophiles- growth optima between 45C and 80C
Hyperthermophiles- greater than 80C (hot springs) chemoorganotrophic and chemolithotrophic species are present

Question 24

What are the molecular adaptations that support psychrophily (cold)?

Answer 24

Production of enzymes that function optimally in the cold
More alpha helicase than beta sheets
More polar and less hydrophilic amino acids
Fewer weak bonds
High unsaturated fatty acid content in cytoplasmic membrane

Question 25

What is acidic pH and what is alkaline pH? What is each microbes pH range?

Answer 25

Acidic pH<7
Alkaline pH>7
Each Microbe has a pH range of roughly 2-3 pH units while most natural environments are pH 3-9

Question 26

What are neutrophiles, acidophiles, and alkaliphiles pH’s?

Answer 26

Neutrophiles- pH 5.5-7.9
Acidophiles- pH < 5.5
Alkaliphiles- pH > or equal to 8

Question 27

What is water activity (aw)?

What is osmosis?

Answer 27

Water availability defined as ratio of vapour pressure of air in equilibrium with a substance or solution to the vapour pressure of pure water

Osmosis is water diffusing from high to low concentrations

Question 28

Why is there a tendency for water to move into the cell?

Answer 28

The cytoplasm has a higher solute concentration that the surrounding environment typically so water tends to move into cell

Question 29

What are aerobes, microaerophiles, facultative organisms, anaerobes, aerotolerant anaerobes, and obligate anaerobes?

Answer 29

Aerobes- requires oxygen and grow at full oxygen tension
Microaerophiles- can use oxygen when it is present at levels reduced from that in air
facultative organisms- can live with or without oxygen
Anaerobes- cannot respire oxygen
Aerotolerant anaerobes- tolerations oxygen and grow in its presence even though they cannot respire
Obligate anaerobes- inhibited or killed by oxygen

Question 30

How do you control microbial growth?

Answer 30

Growth control by heat
Other physical control methods: radiation and filtration
Chemical control of microbial growth