Genetics and Phenotype

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Questions and Answers

What is the term used to describe the observed expression of the genetic determinants?

Mutagenesis

Genotype

Allele

Phenotype (correct)

What are the alternative forms of a gene that result from nucleotide sequence changes?

Alleles (correct)

Genotype

Mutations

Phenotype

What is the process of change in genetic material?

Mutagenesis (correct)

Recombination

Replication

Repair

What are the altered genes that result from mutations?

Mutant alleles Signup and view all the answers

What are the physical, chemical, or physicochemical agents capable of increasing the frequency of mutations?

Mutagens Signup and view all the answers

Why are mutants usually easier to recognize in bacterial cells?

Because bacterial cells are haploid Signup and view all the answers

What is the system used to designate genes based on their function?

A three-letter code Signup and view all the answers

What is the term used to describe the mutations that occur at a constant frequency in the absence of external influences?

Spontaneous mutations Signup and view all the answers

What is the approximate weight of a teaspoon of packed E. coli cells?

1 gram Signup and view all the answers

What is the percentage of water in an average cell?

70% Signup and view all the answers

What is the approximate volume of a cell?

9 × 10^−13 ml Signup and view all the answers

What is the approximate number of ribosomes in a rapidly growing cell?

18,700 Signup and view all the answers

What is the approximate number of different varieties of protein in a cell?

1000-2000 Signup and view all the answers

What is the approximate time it takes for an E. coli cell to make a perfect copy of itself?

40 minutes Signup and view all the answers

How many precursor metabolites are needed to copy a cell?

13 Signup and view all the answers

What is the percentage of the cell volume that the periplasmic space forms?

30% Signup and view all the answers

What is the main function of endospores in microbial physiology?

To provide a selective advantage for survival and dissemination of the species Signup and view all the answers

What is the structure shown in Fig. 1-15?

A mature spore of Clostridium botulinum Signup and view all the answers

What is the correct order of events in the growth of a cell?

Entrance of basic nutrients, replication of the chromosome, conversion of compounds into energy, increase in size and mass, division of the cell Signup and view all the answers

What is the term for the increase in population of microorganisms?

Population increase Signup and view all the answers

What is the function of ribosomes in the spore interior?

To synthesize proteins Signup and view all the answers

What is the term for the process of cell growth and division?

Growth cycle Signup and view all the answers

What is the function of the exosporium in a mature spore?

To protect the spore from extreme conditions Signup and view all the answers

What is the correct definition of growth in microbial physiology?

The culmination of an ordered interplay among all physiological activities of the cell Signup and view all the answers

What determines growth rate in a batch culture?

Properties of the bacteria themselves Signup and view all the answers

What is the purpose of a chemostat?

To grow bacteria at high cell density and slow growth rates Signup and view all the answers

What is the primary source of carbon for lithotrophs?

Carbon dioxide Signup and view all the answers

What is the term for organisms that gain energy through the oxidation of inorganic compounds?

Chemolithotrophs Signup and view all the answers

What is the primary source of energy for photoorganotrophs?

Light Signup and view all the answers

What do microorganisms require to support growth?

Sources of carbon, nitrogen, energy, and essential growth factors Signup and view all the answers

What is the purpose of the overflow device in a chemostat?

To remove medium and cells from the culture vessel Signup and view all the answers

What determines the growth rate in a chemostat?

Rate of fresh medium added to the culture vessel Signup and view all the answers

What is the approximate relationship between the number of viable cells and nonviable cells during the stationary phase?

The number of viable cells is approximately equal to the number of nonviable cells Signup and view all the answers

What is the primary factor that determines the shape of the death phase?

The type of organism being observed Signup and view all the answers

What is the formula for determining the generation time (tg) or doubling time?

tg = t / n Signup and view all the answers

What type of culture is typically used to grow bacteria?

Batch culture Signup and view all the answers

What is the relationship between the number of cells in a population (b) and the number of cells in the initial inoculum (a)?

b = a × 2n Signup and view all the answers

What is the primary reason for the decline in viable population during the death phase?

The death of organisms in the population Signup and view all the answers

What is the purpose of solving the equation for n?

To determine the number of generations that occurred between inoculation and sampling Signup and view all the answers

What is the first step in the process of protein synthesis?

The enzyme RNA polymerase locates the beginning of a gene (promoter). Signup and view all the answers

What is the role of ribosomal ribonucleic acids (rRNA) in protein synthesis?

They form the architectural scaffolding that directs assembly of the proteins to form a ribosome. Signup and view all the answers

What is the term for the RNA molecule that carries genetic information from DNA to the ribosome?

Messenger RNA (mRNA) Signup and view all the answers

What is the process by which the genetic information contained within DNA is processed to produce proteins?

Both transcription and translation Signup and view all the answers

What is the role of the anticodon in translation?

It base-pairs with the codon in mRNA. Signup and view all the answers

What is the term for the enzyme responsible for transcribing RNA from DNA?

RNA polymerase Signup and view all the answers

What is the term for the process by which the enzyme RNA polymerase locates the beginning of a gene (promoter)?

Initiation Signup and view all the answers

What is the term for the tRNA molecule that has an attached amino acid?

Charged tRNA Signup and view all the answers

What is the term used to describe the inhibition of enzyme 1 activity due to excessive production of intermediate B?

Feedback inhibition Signup and view all the answers

What is the result of an excess intracellular concentration of end-product C on enzyme 1?

Genetic repression of enzyme 1 Signup and view all the answers

What is the genetic process by which substrates stimulate the transcription of genes?

Induction Signup and view all the answers

What is the mechanism by which amino acids regulate their own biosynthesis?

Genetic repression Signup and view all the answers

What is the purpose of genetic repression in amino acid biosynthesis?

To prevent the overproduction of amino acids Signup and view all the answers

What is the difference between feedback inhibition and genetic repression?

Feedback inhibition occurs at the enzyme level, while genetic repression occurs at the transcriptional level Signup and view all the answers

What is the outcome of the sequence of purine and pyrimidine bases in a gene?

Specification of the sequence of amino acids incorporated into a polypeptide chain Signup and view all the answers

What is the role of transcription in the central dogma?

Synthesis of RNA from DNA Signup and view all the answers

What is the end result of the process shown in Fig. 1-9?

Repression of enzyme synthesis Signup and view all the answers

What is the term for a heritable unit of function composed of a specific sequence of purine and pyrimidine bases?

Gene Signup and view all the answers

What is the relationship between the genotype and the sum total of all hereditary units of genes?

The genotype is the sum total of all hereditary units of genes Signup and view all the answers

What is the outcome of the base sequence in an RNA molecule?

Specification of the sequence of amino acids incorporated into a polypeptide chain Signup and view all the answers

What is the role of the sequence of purine and pyrimidine bases in a gene?

Specification of the sequence of amino acids incorporated into a polypeptide chain Signup and view all the answers

What is the relationship between the sequence of amino acids in a polypeptide chain and the genotype of an organism?

The genotype determines the sequence of amino acids Signup and view all the answers

What is the characteristic feature of Type III interpeptide bridges?

All of the above Signup and view all the answers

What type of interpeptide bridge is found in B.rettgeri?

Type IV Signup and view all the answers

What is the common feature of Type III and Type IV interpeptide bridges?

Both are composed of peptides Signup and view all the answers

What is the function of lipoprotein molecules in E. coli?

To anchor the outer membrane to the peptidoglycan layer Signup and view all the answers

What is the function of LamB in E. coli?

To serve as a receptor for bacteriophage λ Signup and view all the answers

What is the function of interpeptide bridges in peptidoglycan?

To provide structural support Signup and view all the answers

What is the difference between Type III and Type IV interpeptide bridges?

Type III is found in Micrococcus luteus, while Type IV is found in B.rettgeri Signup and view all the answers

Which of the following porins forms a single, small, highly anion-selective channel?

OmpP Signup and view all the answers

What is the result of mutants lacking Lpp and OmpA in E. coli?

Spherical morphology and abundance of blebbing of the outer membrane Signup and view all the answers

What is the composition of Type III interpeptide bridges?

One to several peptides with the same amino acid sequence as the peptide unit attached to muramic acid Signup and view all the answers

What is the function of the outer membrane in E. coli?

To protect the cell from hydrophobic antibiotics Signup and view all the answers

What is the primary function of OmpC and OmpF in E. coli?

To constitute components of general porins Signup and view all the answers

What is the structure of the OmpF porin of E. coli?

Coalescing channels Signup and view all the answers

What is the common feature of OmpF and PhoE porins?

They both form multiple channels Signup and view all the answers

What is the characteristic feature of Type IV interpeptide bridges?

They extend between carboxyl groups belonging to D-alanine or D-glutamate Signup and view all the answers

What is the purpose of studying interpeptide bridges in peptidoglycan?

To understand the structure of bacterial cell walls Signup and view all the answers

What is the primary difference between OmpF and OmpC?

Their expression regulation by osmolarity Signup and view all the answers

What is the function of porin proteins in E. coli?

To regulate nutrient transport Signup and view all the answers

What is the common feature of most porins from E. coli, P. aeruginosa, and Y. pestis?

They are all cation-selective Signup and view all the answers

What is the name of the protein porin that forms a single anion-specific channel in P. aeruginosa?

Protein P Signup and view all the answers

What is the function of OmpP porin in P. aeruginosa?

To form a single, small, highly anion-selective channel Signup and view all the answers

What is the effect of losing outer membrane lipoprotein (Lpp) and OmpA on the cell envelope and shape of E. coli?

Spherical morphology and abundant blebbing of the outer membrane Signup and view all the answers

How many separate channels do PhoE porins form?

Three Signup and view all the answers

What is the significance of Mg2+ and Ca2+ for the growth of E. coli mutants lacking Lpp and OmpA?

They are required in increased amounts for growth Signup and view all the answers

What is the function of the enzymes encoded by genes in the rfe and rfb gene clusters?

To catalyze the biosynthesis of ECA Signup and view all the answers

What is the composition of the trisaccharide repeat units of ECA?

GlcNAc, ManNAcA, and Fuc4NAc Signup and view all the answers

What is the function of the genes in the rff gene cluster?

To catalyze the biosynthesis of ECA Signup and view all the answers

What is the name of the enzyme responsible for the first stage of lipid A biosynthesis?

LpxA Signup and view all the answers

What is the product of the second stage of lipid A biosynthesis?

Disaccharide-1-P Signup and view all the answers

What is the function of the third stage of lipid A biosynthesis?

KDO transfer and late acylation Signup and view all the answers

Why are the rfe and rfb gene clusters involved in both LPS and ECA biosynthesis?

Because both LPS and ECA require common intermediates for their synthesis Signup and view all the answers

What is the structure of the ECA cell surface glycolipid?

A heteropolymer containing GlcNAc, ManNAcA, and Fuc4NAc Signup and view all the answers

What is the main component of the nucleosome core in eukaryotic chromosomes?

146 bp of DNA and an octomer of four major histone proteins Signup and view all the answers

What is the function of the histone-like protein HU in E. coli?

To stabilize higher-order nucleoprotein structures Signup and view all the answers

What is the configuration of nucleosomes in the repeating unit of DNA organization?

A beads-on-a-string Signup and view all the answers

How many major histone proteins form the octomer in the nucleosome core?

Four Signup and view all the answers

What is the approximate size of the bar in the diagram?

1.0 µm Signup and view all the answers

What is the role of histones in eukaryotic chromosomes?

To determine the conformation of chromatin Signup and view all the answers

How many kDa subunits are present in the HU protein?

10 Signup and view all the answers

What is the purpose of X-ray diffraction in studying nucleosomes?

To visualize the structure of nucleosomes Signup and view all the answers

What is the term used to describe the DNA-containing region of the cell in most bacteria?

Nucleoid Signup and view all the answers

What is characteristic of the nuclear membrane in eukaryotic cells?

It has prominent pores Signup and view all the answers

What can be seen lining the rough endoplasmic reticulum in Figure 7-1?

Ribosomes Signup and view all the answers

What is the term used to describe the region between the nucleus and the plasmalemma in Figure 7-1?

Cytoplasm Signup and view all the answers

What is the function of the structures shown in Figure 7-2 (b)?

Protein synthesis Signup and view all the answers

What is the characteristic of the cell wall in Figure 7-2 (a)?

It is a rigid structure Signup and view all the answers

What is the term used to describe the distinct region within a bacterium where the chromosome is folded?

Nucleoid Signup and view all the answers

What is the difference between eubacteria and archaebacteria in terms of their nuclear membrane?

Some species of eubacteria and archaebacteria have a nuclear membrane Signup and view all the answers

What is the purpose of having multiple nucleoids in fast-growing bacterial cells?

To facilitate rapid cell doubling during fast growth Signup and view all the answers

During cell division, when does the separation of the duplicating nucleoid occur?

During the S phase Signup and view all the answers

What is the role of proteins like ParB in Caulobacter crescentus and SpoOJ in Bacillus subtilis?

To direct the oriC region toward the poles Signup and view all the answers

What is the term used to describe the occurrence of multiple copies of nucleoids or entire chromosomes in bacteria?

Multiploidy Signup and view all the answers

What is the purpose of fluorescence microscopy studies in bacteria?

To study the movement of immunolabeled nucleoids during replication and cell division Signup and view all the answers

What is the stage of the cell cycle during which DNA replication occurs?

S phase Signup and view all the answers

What is the result of having multiple nucleoids in bacteria?

Faster cell growth Signup and view all the answers

What is the mechanism by which nucleoids are segregated during cell division in bacteria?

Mitosis-like movement Signup and view all the answers

What is the primary function of histones in eukaryotic chromosomes?

To determine the conformation of chromatin Signup and view all the answers

What is the term used to describe the repeating unit of DNA organization in eukaryotic chromosomes?

Nucleosome Signup and view all the answers

What is the approximate mass of the DNA and histone proteins in a nucleosome core?

146 bp of DNA and an octamer of histone proteins Signup and view all the answers

What is the term used to describe the structure formed by the interaction of genomic DNA with DNA-binding proteins in E. coli?

Nucleoid Signup and view all the answers

What is the function of the HU protein in E. coli?

To stabilize higher-order nucleoprotein structures Signup and view all the answers

What is the approximate size of the subunits of the HU protein in E. coli?

10 kDa Signup and view all the answers

What is the proposed role of the HU protein in E. coli?

To confer specificity during DNA interactions Signup and view all the answers

What is the result of extensive digestion of chromatin with micrococcal nuclease?

Release of nucleosome core Signup and view all the answers

Study Notes

Genetic Determinants

The observed expression of genetic determinants is referred to as the phenotype
An individual gene can exist in different forms as a result of nucleotide sequence changes, known as alleles
Genetic material can change or mutate through a process called mutagenesis
Altered genes are referred to as mutant alleles, in contrast to normal or wild-type alleles

Mutations

Spontaneous mutations can occur during replication, repair, and recombination of DNA due to errors made by enzymes involved in DNA metabolism
Mutations can be increased by environmental influences such as radiation, chemicals, and physical or chemical agents (mutagens)
Induced mutations occur as a result of external influences, whereas spontaneous mutations occur at a constant frequency without external influences

Bacterial Cells

Bacterial cells are haploid, making it easier to recognize mutants
The total weight of an average cell is 9.5 × 10^(-13) g, with water making up 70% of the cell
The dry weight of a cell is 2.8 × 10^(-13) g, composed of protein, RNA, DNA, lipids, lipopolysaccharides, peptidoglycans, and other components

Cell Structure

The periplasmic space makes up 30% of the cell volume
One teaspoon of packed E. coli weighs approximately 1 gram (wet weight) and contains about one trillion cells
The bacterial cell contains two copies of the chromosome when growing rapidly, as well as 18,700 ribosomes and over 2 million total molecules of protein

Cell Growth

Growth is the culmination of an ordered interplay among all physiological activities of the cell
The growth cycle consists of five stages: entrance of basic nutrients, conversion of nutrients into energy and vital cell constituents, replication of the chromosome, increase in size and mass, and division of the cell into two daughter cells

Growth Curve

A typical growth curve for a bacterial culture shows a lag phase, exponential phase, stationary phase, and death phase
The stationary phase represents an equilibrium between the number of cells able to divide and the number that are unable to divide
The death phase may assume a linear function depending on the nature of the organism and factors contributing to cell death

Growth Rate

The number of cells in a population (b) is equal to the number of cells in the initial inoculum (a) × 2^n
The generation time (tg) or doubling time can be determined by dividing the time elapsed (t) by the number of generations (n)

Continuous Culture

Continuous culture allows for the growth of bacteria at different rates and high cell density
A chemostat is used to add fresh medium containing a limiting nutrient at a set rate, allowing for external control of growth rate

Factors Affecting Growth

Nutrition: all living organisms require sources of carbon, nitrogen, energy, and essential growth factors
Microorganisms vary widely in their nutritional requirements, with two main groups classified based on their ability to gain energy from certain sources:
- Lithotrophs: utilize carbon dioxide as the sole source of carbon and gain energy through oxidation of inorganic compounds or light
- Organotrophs: prefer organic substrates as a source of energy and carbon

Chromosomal Segregation and Cell Division

Chromosomal segregation must occur before the cell completes construction of the cross-wall that separates the two offspring cells.

Protein Synthesis (Translation)

The genetic information in DNA is processed in two steps to produce proteins.
The enzyme RNA polymerase locates the beginning of a gene (promoter) and transcribes RNA from the DNA template.
The RNA, called messenger RNA (mRNA), is transcribed before being completely translated into protein.
A ribosome attaches to the beginning of the mRNA and translates it into protein by reading three nucleotides (triplet codon) as a specific amino acid.
Each amino acid must be attached to an adaptor or transfer RNA (tRNA) molecule specific for that amino acid.
The tRNA molecule containing an attached amino acid is referred to as a charged tRNA molecule.
The anticodon of the tRNA molecule base-pairs with the codon in mRNA.

Transcription and Translation

The sequence of events involved in transcription and translation is depicted in Figure 1-8.
The ribosome translates mRNA into protein by reading three nucleotides (triplet codon) as a specific amino acid.

Genetic Terms

A gene is a heritable unit of function composed of a specific sequence of purine and pyrimidine bases.
The genotype of an organism is the sum total of all of the hereditary units of genes.

Genetic Regulation

Genetic repression is the inhibition of enzyme synthesis by the end product of the reaction.
Induction is the stimulation of enzyme synthesis by the substrate of a pathway.
Hypothetical pathways illustrating genetic repression and induction are presented in Figure 1-9.
Feedback or end-product inhibition occurs when excessive production of an intermediate results in the inhibition of an enzyme activity.
Genetic repression occurs when an excess of end-product C inhibits the transcription of genes encoding the biosynthetic enzymes.

Nucleosomes

Eukaryotic chromosomes are organized into DNA-protein complexes called nucleosomes
Proteins, mainly histones, play an important role in determining the conformation of eukaryotic chromosomes, referred to as chromatin
Nucleosomes are frequently seen in a "beads-on-a-string" configuration
Extensive digestion of chromatin with micrococcal nuclease releases the nucleosome core, a small, well-defined particle
The particle mass is equally distributed between 146 bp of DNA and an octomer formed by two each of four major histone proteins (H2A, H2B, H3, and H4)

Histone-like Proteins in E. coli

The genomic DNA of E. coli is compacted into a nucleosome-like structure by interaction with several DNA-binding proteins
As many as 12 species of nucleoid proteins have been identified
Histone-like protein HU contains two closely related 10 kDa subunits, HU-α and HU-β, encoded by hupA and hupB
HU protein is involved in stabilizing higher-order nucleoprotein structures to confer specificity during DNA interactions

Peptidoglycan and Interpeptide Bridges

Type III bridge: composed of one to several peptides, each having the same amino acid sequence as the peptide unit attached to muramic acid; found in Micrococcus luteus
Type IV bridge: extending between carboxyl groups belonging to either D-alanine or to D-glutamate and a diamino acid residue or a diamino acid-containing short peptide; found in B. rettgeri

Porins and Cell Surface

Porins facilitate the entry of specific metabolites into the cell
OmpF and OmpC are general porins that allow hydrophilic solutes of a molecular weight less than 700 to traverse the outer membrane
OmpF forms coalescing channels, while PhoE porin forms three separate channels
Pseudomonas aeruginosa forms a single, small, highly anion-selective channel (OmpP)
Most porins appear to be cation selective, while only a few show anion selectivity

Outer Membrane and Lipoprotein

Lipoprotein molecules serve to anchor the outer membrane to the peptidoglycan layer
Mutants lacking lipoprotein and OmpA display spherical morphology and abundant blebbing of the outer membrane
Lipoprotein is essential for maintaining the association of the murein layer with the outer membrane

Lipopolysaccharide Biosynthesis

The three components of LPS (O-antigen, core oligosaccharide, and lipid A) are synthesized independently of each other and later ligated in or on the inner membrane
LPS is translocated to the outer membrane after assembly
Enterobacterial common antigen (ECA) is a cell surface glycolipid synthesized by all members of the Enterobacteriaceae
ECA is a heteropolymer containing N-acetyl-D-glucosamine, N-acetyl-D-mannosaminuronic acid, and 4-acetamido-4,6-dideoxy-D-galactose linked together to form chains of trisaccharide repeat units

Lipid A Biosynthesis

Lipid A biosynthesis in E. coli involves three stages: UDP-GlcNAc acylation, disaccharide formation and 4' kinase action, and KDO transfer and late acylation
Enzymes encoded by genes in the lpxA, lpxC, lpxD, lpxB, and kdtA genes are involved in lipid A biosynthesis

Bacterial Nucleoids

Bacterial nucleoids are not bound by a nuclear membrane, unlike eukaryotic nuclei.
Fast-growing cells can display multiple nucleoids due to multifork replication, facilitating rapid cell doubling.
The presence of multiple copies of nucleoids or entire chromosomes (multiploidy) is common in many bacterial species.
Separation of duplicating nucleoids during cell division occurs during the S phase.
Fluorescence microscopy studies reveal a mitosis-like movement of immunolabeled nucleoids during replication and cell division in bacteria.

Protein Components of Chromosomal Segregation Apparatus

Protein components, such as ParB in Caulobacter crescentus and SpoOJ in Bacillus subtilis, direct the oriC region toward the poles.
These proteins appear to move toward the poles in a mitosis-like manner in concert with oriC.

Nucleosomes

Eukaryotic chromosomes are organized into DNA-protein complexes termed nucleosomes.
The proteins, mainly histones, play an important role in determining the conformation of eukaryotic chromosomes, referred to as chromatin.
Nucleosomes are frequently seen in a "beads-on-a-string" configuration.
The nucleosome core is a small, well-defined particle that has been crystallized, with a particle mass equally distributed between 146 bp of DNA and an octomer formed by two each of four major histone proteins (H2A, H2B, H3, and H4).

Nucleoid Proteins in E. coli

The genomic DNA of E. coli is compacted into a nucleosome-like structure by interaction with several DNA-binding proteins.
As many as 12 species of nucleoid proteins have been identified, including the histone-like protein HU.
HU protein contains two closely related 10 kDa subunits, HU-α and HU-β, encoded by hupA and hupB.
HU protein is involved in stabilizing higher-order nucleoprotein structures to confer specificity during DNA interactions.

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Description

This quiz covers the basics of genetics, including the concept of phenotype, alleles, and mutagenesis. It explores the changes in genetic material and their effects on an organism.