Microbiology Chapter 8: Microbial Genetics

Define genome.

genetic information in a cell

Define chromosomes.

structures containing DNA and protein that physically carry genes

Define genes.

segments of DNA that code for a functional product

Describe the components that make up the nucleotides.

phosphate, pentose sugar, nitrogenous base

Describe some differences between RNA and DNA

DNA: double stranded, thymine as a nucleotide, pentose sugar deoxyribose has no -OH on the second carbon

RNA: single stranded, uracil as a nucleotide, pentose sugar ribose has an -OH on the second carbon

Why does DNA have two strands of DNA?

the base pairs make DNA more stable

What are characteristics of DNA strands?

antiparallel and base pairs are complementary

What are the base pairings in DNA?

adenosine (A) with thymine (T)

cytosine (C) with guanine (G)

Describe the process of DNA replication.

DNA unwinds, creating a replication fork with one strand acting as a template strand. 2 DNA strands are synthesized by DNA polymerase in opposing directions (bidirectionally) from 5' to 3', then DNA rewinds.

How does DNA replication proceed?

bidirectionally from the origin of replication

How does DNA polymerase replicate DNA?

reads and adds complementary nucleotides in DNA replication

Describe the central dogma of molecular biology.

genetic information is contained in DNA, which is transcribed into RNA, then RNA is utilized and translated into proteins

What are the three types of RNA?

mRNA, rRNA, tRNA

What is mRNA?

messenger RNA -- this carries coding info for making specific proteins from DNA to ribosomes

What is rRNA?

ribosomal RNA -- this is an integral component of ribosomes as it is the functional core

What is tRNA?

transfer RNA -- this carries the amino acid to ribosome for protein synthesis

Describe the process of transcription.

genetic material from DNA is transcribed as RNA by RNA polymerase, with all synthesis occuring in 5' to 3' direction, antiparallel, and complementary base pairs

Where does transcription occur in prokaryotes? Eukaryotes?

prokaryotes: cytoplasm, eukaryotes: nucleus

What is the template for transcription?

the DNA strand that corresponds to the desired gene

Which enzyme transcribes the genetic material?

RNA polymerase

Describe the process of translation.

the transcribed RNA strand is translated into amino acids that designate the function of the protein

How does the RNA determine the function of the protein?

by specifying the order of the amino acid in the protein

Define a codon.

a 3-nucleotide sequence that codes for an amino acid

What does it mean for the genetic code to be degenerate?

some amino acids have more than one codon, but each codon only has ONE meaning (unambiguous)

How many codons are accounted for in the genetic code? How many are considered sense and stop codons?

there are 64 codons -- 61 sense codons, 3 nonsense codons

What is the MET/start codon?

AUG codes for methionine/start

What are the three stop codons?

UGA, UAA, UAG

How does the ribosome know when to stop translation and release the polypeptide?

a release factor (stop codon) will bind to the A site and the ribosome will release the polypeptide

Define polyribosomes.

many ribosomes can bind to a single mRNA strand and translate it

Why can translation occur before transcription is completed?

because prokaryotes lack a nucleus, translation and transcription occur in the same area

How do polyribosomes affect protein synthesis?

increases rate of output

If transcription proceeds to the left and reads 5' to 3', what direction will the DNA strand be read?

3' to 5'

Define a mutation.

permanent change in base sequence of DNA

Define point mutation.

change in one nucleotide base pair

Define missense mutation.

nucleotide change causes substitution of one amino acid for another

Define nonsense mutation.

nucleotide change results in a premature stop codon

Define silent mutation.

change in nucleotide base pair does not result in a change of the amino acid coded by the gene

How is sickle cell anemia caused?

by a point mutation that causes glutamic acid (GAG) to become valine (GTG), which distorts hemoglobin

Define frameshift mutation.

a nucleotide is added or deleted, resulting in a shift in the entire sequence from that point on

What is the most damaging mutation?

frameshift mutations

How does UV radiation cause mutations?

UV can cause thymine-thymine dimerization and, unless repaired, will result in damage or death to the cells because it inhibits transcription + replication

How can thymine-thymine dimers be repaired?

nucleotide excision repair

How does nucleotide excision repair occur?

Series of enzymes create a break, excise the problem area, and create a new one to add in. Must be fixed before DNA is copied

In Frederick Griffith's experiment with streptococcus pneumoniae, what happened to the mouse that was injected with the smooth (S) strain?

mouse died

In Frederick Griffith's experiment with streptococcus pneumoniae, what happened to the mouse that was injected with the rough (R) strain?

mouse lived

In Frederick Griffith's experiment with streptococcus pneumoniae, what happened to the mouse that was injected with the heat-killed smooth (S) strain?

mouse lived

In Frederick Griffith's experiment with streptococcus pneumoniae, what happened to the mouse that was injected with the heat-killed smooth (S) strain and living rough (R) strain?

mouse died

Why did the mouse die when injected with both the heat-killed S strain and living R strain?

the living R strain absorbed the DNA from the dead S strain, causing the R strain to become virulent

Why was the smooth (S) strain virulent?

the smooth (S) strain was protected by a polysaccharide capsule that prevents its detection by the host's immune system

What is the "transforming principle"?

DNA

What are two other ways that DNA can be transferred between cells?

conjugation and transduction

Define conjugation.

attachment of two related species via bridge (pilus) to transport DNA

Define transduction.

DNA transferred via virus -- bacteriophages infect the donor bacterial cell. bacterial DNA is then packaged in the phage capsid and is released to infect a new host cell, which can facilitate recombination and increase genetic diversity.