Microbiology Ch 6. Microbial Genetics

Genetics

the study of inheritance or heredity:

• transmission of biological properties (traits) from parents to offspring

• How those traits are expressed

• Structure and function of genetic material

• how material changes

Chromosomes in Eurkaryotes and Prokaryotes are different

Eukaryotic chromosomes consist of DNA tightly wound around histone proteins located; nucleus

Prokaryotic chromosomes are condensed and jammed into a packet form by histone-like proteins;located; cytoplasm

Accurate statement regards to genotype or phenotype of an organism

The alleles contained within the cells of an organism comprise its genotype

Genome

Sum total of the genetic material of an organism

** Most genomes exist in the form of chromosomes

*Some of an organisms genome may appear in non chromosomal forms:

-plasmids tiny extra pieces of DNA separate from bacterial chromosome

DNA double stranded characteristics;

2 nanometers in width

10 base pairs per turn

34 nanometers per basepair

DNA sequence is complemtary to 5’TAGAC3’?

3’ATCTG5’

Helicase

The enzyme that unwinds a segment of DNA molecule| unzipping DNA Helix

Primase

Synthesizing an RNA primer

DNA polymerase I

Responsible for removing the primer, closing gaps in the DNA and repairing mismatched bases

Ligase

Responsible for the final binding of nicks in DNA during replication

Topoisomerases I and II

Responsible for supercoiling and untangling of DNA

MRNA processing in Eukaryotes

Transposons

Transposable DNA elements

Which does not directly involve DNA?

Translation

In a protozoal or fungal cell, chromosomes are located in the (blank)

nucleus

DNA segments that code for proteins are referred to s (blank) genes

structural

Genomics

study of complete sets of genes

Genotype

Sum of all genes that constitute an organism’s distinctive genetic makeup

**ALL organisms contain more genes in their genotype than are manifested as a phenotype at any given time. phenotype can change depending on what genes are activated and being expressed

Phenotype

Expression of the genotype;certain structures or functions are created

Sizes; Ecoli has single chromosome with 4000-5000 genes

Chromosome 1mm long if unwound and stretched but it is still 1000 times longer than the cell.

** A human cell has 23,000 genes on 46 chromosomes and about 6 feet long.

Nucleotide

Basic unit or building block

-phosphate group

-Deoxyribose sugar

Purines and pyrmidines

*Adenine always pairs with Thymine

*Guanine always pairs with Cytosine )

^ always called complementary base pairing

DNA;

has an antiparrallel arrangement

**SIgnificance of DNA structure- genetic code is maintained during reproduction

*this is assures by the constancy of base pairing in a DNA molecule

Semiconservative replication:

DNA molecule unzips the hydrogen bonds between complementary nitrogenous bases are broken

*the original DNA strands are called parental strands in the new daughter strand

-Each strand is made up of one conservative and one new one.

DNA Polymerase III

*Synthesizes a new daughter strand of DNA using the parental strand as a template

*DNA molecule must be unwound and separated before DNA polymerase III can function

Replication Fork;

A place in the helix where two DNA strands are unwound and replication is taking place

-In bacteria each circular DNA molecule will have two replication forks from a single origin,

Eukaryotes have multiple replication forks from multiple origins

*Leading strand: strand of new DNA that is synthesized continously in a 5’ to 3’ direction-heading towards the opening replication fork

*Lagging strand: strand of new DNA that must be synthesized non-continously heading away from the opening replication fork

Primer

*A length of RNA that is inserted initially during replication by DNA primase for DNA polymerase III to start making a new DNA strand

Concept Check: A gene is:

a. A fundamental unit of heredity

b. a specific portion of DNA along on a chromosome

c. A segment of DNA that codes for a protein or RNA molecule

d. comfortable pants

a,b, and c

Central Dogma

states genetic information in a cell flows from DNA to RNA to a protein

What is the connection between DNA and an organisms trait?

proteins primary structure determines its characteristics shape and function

*Proteins ultimately determine phenotype

Proteomics: study of organisms complete set of expressed proteins.

DNA vs RNA

DNA- double stranded while RNA is single stranded

DNA sugar is deocyribose while RNA is ribose

Structural Genes

DNA segments that code for proteins

Characteristics resulting from interaction of that particular genetic makeup of an organism and the environment is the (blank) of that organism

phenotype

Different type of nucleotides in DNA contain

Same sugar and phosphate but different nitrogenous bases

Adenine and Guanine

both are purines

Antiparallel orientation of strands in DNA

One strand is 5’to 3’ and the other is 3’to5’

Match number of genes with its genome:

Virus- few dozen

Bacterium- few thousand

Human- ten thousand

Ensuring that the DNA code will be maintained during cell growth and cell (blank) is one of the two essential effects of the structure of DNA

replication

In DNA replication (blank) unwinds (unzips) the double helix, primase synthesize the short RNA primer and DNA (blank) adds nucleotides to the new chain

helicase, polyermase

what is true regarding DNA replication?

Each new DNA helix contains one parent strand and one newly synthesized strand

What is the main enzyme in elongation of a DNA strand during replication?

DNA polymerase

During DNA replication the newly made double helices are composed of one parent template and one newly synthesized strand and therefore the replication is considered (blank)

semiconservative

During DNA replication, the lagging strand is replicated in a discontinous manner forming (blank) fragments

okazaki

Enzymes that function in DNA replication

-Helicase

-ligase

-DNA polymerase

The Y-shaped point on a replicating DNA molecule where the DNA polymerase is synthesizing new strands of DNA is (blank) fork

replication

DNA polymerase synthesize new strands of DNA in

the 5’ to 3’ direction only

Ligase

final sealing of nicks in a newly synthesized DNA strand

How many replication forks are formed from opening a section of a circular DNA molecule during replication

2

During DNA replication why are primer sequences necessary?

Primers provide DNA polymerase with the 3’end needed for synthesis

In central dogma;

DNA is copied to RNA in a process called transcription and RNA is used to direct the synthesis of a protein in a process called translation

What is the function of mRNA

it carries a copy of DNA sequence to the ribosome

rRNA

RNA comprises ribosomal subunits

Length of typical tRNA molecule

75-95 bases

What occurs during Transcription termination?

RNA polymerase reaches a terminator region

The process of transcription (blank) results in release of a completed RNA transcript

termination

Translation Elongation

-formation of peptide bond between amino acids in A and P sites

-tRNA delivers amino acid to empty A site

How many stop codon are contained within the genetic code

3

Which 3 events in protein synthesis occur post translationally?

• Removal of formyl methiononine

• Protein folding

• Addition of cofactor

Stop Codon-

UAA,UAG, UGA

The genes of which microorganism are arranged as operons

bacteria

Finishing touches on proteins are (blank) modification

posttranslational

The (blank) of the lac operon is comprised of three genes, each encoding a different enzyme needed to catabolize lactose

structural locus

The lactose operon has 3 important components;

the regulator, a gene that codes for a protein (a repressor) capable of repressing the operon

Phase variation

process of bacteria turning on or off a group of genes that chages their phenotype in a heritable manner

The lactose repressor protein binds to the (blank) of the lac operon

operator

which process in bacteria do abx in group erythromycin inhibit?

Protein synthesis

• they also prevent translation

Three methods of gene transfer:

Conjugation, transformation and generalized transduction

Plasmid

A small circular piece of DNA that replicates its nonessential genes independently of the chromosome

During which method of gene transfer are bacterial cells in direct contact?

Conjugation

Transformation

Acceptance by a bacterial cell of small fragments of DNA from the surrounding environmnent; uptake of free DNA by competent bacterial cells

Transduction

Method of DNA recombination in bacteria that involves transfer of DNA via bacteriophages

Transposons also called “jumping genes”

Insertion sequences that can lead to changes in genotype within a cell or between cells

*Involved in; changes in traits such as

1.) colony morphology, pigmentation, and antigenic characteristics

2.) replacement of damaged DNA

3.)transfer drug resistance between bacteria

Pathogenicity Islands

Areas of genome contain multiple genes which contribute to a new trait for the organism that increases its ability to cause disease

Transposons;

Replacement of damagede DNA

Inter-microbial transfer of drug resistance

Phenotypic changes in colonies

Missense mutation

Any changes in the code that leads to placement of a different amino acid;

functions’

*1.) create faulty nonfunctional protein

2.) produce a protein that functions in a different manner

3.)cause no significant in protein function

Which of the following is repsonisble for spontaneous mutations?

Errors in DNA replication

A mutation that affects only a single base pair in DNA is termed (blank)

point

When a mutation changes a base, but does not change amino acids sequence of the encoded protein

silent mutation

Nonsense mutation

Early termination of a protein

A mutation that changes a base but does not change amino acid sequence of endoded protein

Silent mutation

Photoactivation

process repairs DNA that has been damaged by UV radiation using visible light

Frameshift mutation

Most harmful mutations to cells

Which test is a method of detecting mutagenic and potentially carcinogenic agents based upon genetic alteration of nutritionally defective bacteria

Ames