Microbiology Ch 8

Point mutations

(Base substitution) single base at one point is replaced w/ a different base.

What two ways can mutations be repaired?

1. Nucleotide excision repair- enzymes are cut out and replace the damaged portion of DNA. (Not restricted) 2. Photolyases (light repair enzymes)- use visible light energy to separate the dimer back to the original two thymines in UV-induced damage.

DNA replication

1. The double helix of the parental DNA separates as weak hydrogen bonds between the nucleotides on opposite strands break in response to the action of replication enzymes. 2. Hydrogen bonds form between new complementary nucleotides and each strand of the parental template to form new base pairs. 3. Enzymes catalyze the formation of sugar-phosphate bonds between sequential nucleotides on each resulting daughter strand.

Protein synthesis

1. Transcription- enzyme RNA polymerase synthesizes a strand of RNA from one of the double-stranded DNA, which serves as a template. (RNA binds to the DNA at the promoter and stops when it reaches the terminator) 2.RNA processing (transcription)- rRNA is an integral part of ribosomes. tRNA transports amino acids during protein synthesis. mRNA carries coded information from DNA to ribosomes. 3. Translation- begins at start codon AUG, ends at nonsense codons UAA, UAG, UGA. Codons of mRNA read sequentially, tRNA (each has an anticodon) transport ribosomes and amino acids are joined by peptide bonds.

Operon

A set of operator and promoter sites and the structural genes they control.

DNA polymerase

Adds nucleotides to the growing DNA strand. Proofreads and repairs DNA. Removes primers.

Mutagen

Agents that cause mutations

Genome

All genetic information in a cell.

Horizontal gene transfer

Bacteria passing there genes laterally to other microbes of the same generation.

Nonsense mutation

Base substitution results in a nonsense/stop codon

Missense mutation

Base substitution results in change in an amino acid.

Why is one strand of DNA synthesized discontinuously?

Because it's the lagging strand.

Why can translation begin before transcription is complete in prokaryotes but not in eukaryotes?

Because mRNA is produced in the cytoplasm in prokaryotes, the start codons of an mRNA being transcribed are available to ribosomes before the entire mRNA molecule is made.

Why can't the RNA transcript be used for translation?

Because translation is the decoding of nucleic acids and converting it to proteins by using the language of mRNA in the form of codons.

Chromosomes

Contain DNA that physically carry hereditary information; chromosomes contain genes.

Transduction

DNA is transferred from a donor cell to a recipient via a bacteriophage.

Genetic recombination

Exchange of genes between two DNA molecules, creates genetic diversity.

Phenotype

Expression of genes

Vertical gene transfer

Genes are passed from an organism to its offspring.

What is the advantage of semiconservative replication?

Genetic information can be transferred vertically to the next generation of cells. (One original and one new.)

Genotype

Genetic makeup

Frameshift mutation

Insertion or deletion of one or more nucleotide pairs.

What is the advantage of degeneracy of the genetic code?

It allows for a certain amount of misreading of or mutation in the DNA without affecting the protein ultimately produced.

DNA ligase

Makes covalent bonds to join DNA strands, Okazaki fragments, and new segments in excision repair.

Do all mutagens cause cancer?

Most are carcinogens.

Does a base substitution always result in a different amino acid?

No because the resulting new codon might still code for the same amino acid.

Spontaneous mutations

Occur in the absence of a mutagen.

What is the origin of replication?

Parental strand

Mutation

Permanent change in the base sequence of DNA

What are the functions of plasmids and transposons?

Plasmids are self replicating circular pieces of DNA. Transposons are segments of DNA that can move from one region of DNA to another.

Conjugation

Plasmids transferred from one bacterium to another. Requires cell-to-cell contact.

DNA gyrase

Relaxes the strands before the replication fork.

Gene

Segments of DNA that encode functional products, usually proteins.

Genomics

Sequencing and molecular characterization of genome.

Genetic code

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

What is an open- reading frame?

Span of genetic material that can be read by genetic machinery to produce a protein.

Why is base pairing in DNA important?

The base sequence of one DNA strand determines the base sequence of the other strand, which makes the 2 stands complementary.

What causes transcription of an inducible enzyme?

The inducer

How does DNA serve as genetic information?

The linear sequence of bases provides actual information. The genetic information is encoded by the sequence of bases along a strand of DNA, like our language it it uses linear sequence of letters to form words/sentences.

What causes transcription of a repressible enzyme?

The repressor

What is a clinical application of genomics?

The use of genomics to track the West Nile virus.

Why are transposons sometimes referred to as "jumping genes"?

They consist of DNA segments that can move from one position on a chromosome to another.

Crossing over

Two chromosomes break and rejoin, resulting in the insertion of foreign DNA into the chromosome.

When does transcription stop?

When RNA polymerase reaches the terminator.

Genetics

the science of heredity; how genes carry information, how information is expressed, and how theyre replicated.

When glucose and lactose are present, why will cells use glucose first?

they grow at their maximal rate with glucose as their carbon source because they can use it more efficiently.