Some questions to guide your study:

• What is the difference between a gene, a chromosome, the genome, a nucleotide, and a base pair?
• How do procaryote and eucaryote chromosomes differ? In what ways are they the same?
• How can the genetic alphabet, with only four letters, code for tens of thousands of different proteins?
• When is DNA replicated, and for what reason? What is the difference between replication and transcription?
  • What is different between procaryote and eucaryote replication?
  • What is meant by leading strand and lagging strand? What does this have to do with Okazaki fragments?
  • How do viruses replicate?
    
• During transcription, what is being copied, and why?
  • What is the difference between DNA and mRNA?
  • In eucaryotes, what is an exon and what is an intron? What is alternative splicing?
    
• What is the difference between transcription and translation? What structures are involved in translation? What is the role of tRNA?
• What is an operon? What is meant by "promoter," "operator," "regulator," and "structural genes?"What about a repressor?
• In what ways could an antibiotic target bacterial transcription or translation?
• In considering point mutations, how is a missense mutation different than a nonsense mutation?
  • Why is a "silent mutation" silent?
  • How is a frameshift mutation caused?
• In what ways besides mutation can bacteria get new genetic combinations?
  • How does conjugation differ from transformation or transduction?

Microbial Genetics
If you are new to genetics, or want a quick review, check out the guided tour of the basics at the U of U Learn Genetics site.

Genetics
Genetics is the scientific study of inherited characteristics given to offspring from parent. It applies to humans and all other living organisms. There are four levels of genetics that are recognized:
Organism level, cell level, chromosome level, and molecular level.



Organism Level: observes the heredity of the whole organism.
Cell Level: examines the heredity of the cell.
Chromosome Level: examines the characteristics and actions of chromosomes.
Molecular Level: deals with the biochemistry of the genes.

Genome: the sum total of genetic material of a cell.
Gene: Fundamental unit of heredity responsible for a given trait.
Chromosome: discrete cellular structure composed of a neatly packaged elongate DNA molecule.

Gene: fundamental unit of heredity responsible for a given trait in an organism.
Nucleotide: the basic unit of DNA structure and main component of DNA. A gene in a bacteria contains several million nucleotides linked end to end. Nucleotides are composed of a phosphate, a deoxyribose sugar, and a nitrogenous base. Nucleotides covalently bond to form a sugar-phosphate linkage that is the backbone of each strand. Each sugar attaches in a repetitive pattern to two phosphates. The nitrogenous bases, purines and pyrimidiens, attach by covalent bonds at the 1' position of the sugar.
Intron: a section of DNA within a gene that doesn't actually code for anything. a sequence of bases in DNA that codes for a protein.
Exon: a sequence of bases in DNA that codes for a protein.
Replicon: the circular bacterial DNA molecule replicates by means of a special configuration.
Transcription: the formation of mRNA using DNA as a template.
Translation: the synthesis of proteins using mRNA as a template.
Transduction: the transfer of genetic material from one microorganism to another by a viral agent (as a bacteriophage).
RNA is encoded like DNA, but its general structure is different in several ways.
Messenger RNA (mRNA): a copy of a structural gene or genes complementary DNA, synthesized by a process similar to the synthesis of the leading strand during DNA replication and the complimentary base-pairing rules ensure that the code will be faithfully copied in the mRNA transcript.
Codons: a series of triplets that read the message transcribed on the mRNA strand.


The DNA Code

The basic unit of DNA structure is the nucleotide. Each of the nucleotides have phosphate, deoxyribose sugar, and a nitrogenous base.
Enzymes Involved in DNA Replication Helicase: Unzipping the DNA helix Primase: Synthesizing as RNA primer DNA polymerase III: Adding bases to the new DNA chain; proofreading the chain for mistakes DNA polymerase I: Removing primer, closing gaps, repairing mismatches Ligase: Final binding of nicks in DNA during synthesis and repair Gyrase: Supercoiling.

Deoxyribose- is a pentose (5-carbon) sugar - formula C5H10O4. It is found in DNA.

Notice the 5 carbon atoms (grey) forming the backbone of the molecule, and the oxygen atom (red) in the ring - which is a 5 sided ring, unlike glucose.
The hydrogen atoms (white) are either attached directly to the carbons, or via oxygen as OH groups - at an angle. The carbon outside the ring has 2 single hydrogen's and an OH group.



Deoxyribose differs from ribose in that it lacks an oxygen at carbon 2 (labelled) - and so has only 2 hydrogen atoms (white).

Q: What term is defined as a certain segment of DNA that contains the necessary code to make a protein or RNA molecule?
a. genome
b. chromosome
c. gene
A: gene

Q: Which statement regarding the structure of the DNA molecule is correct?
a. DNA is anti parallel
b. the nitrogenous bases of the two strands are linked by hydrogen bonds
c. the sequence of base pairs along the DNA molecule is invarient
A: the sequence of base pairs along the DNA molecule is invarient


Enzymes Involved in DNA Replication
Helicase: Unzipping the DNA helix.
Primase: Synthesizing as RNA primer.
DNA polymerase III: Adding bases to the new DNA chain; proofreading the chain for mistakes.
DNA polymerase I: Removing primer, closing gaps, repairing mismatches.
Ligase: Final binding of nicks in DNA during synthesis and repair.
Gyrase: Super-coiling

Q: What enzyme is responisible for coiling the chromosome into a tight bundle by introducing a reversible series of twists into the DNA molecule?
a. DNA Gyrase
b. Helicase
c. Primase
A: DNA Gyrase
Types of Ribonucleic Acid

RNA Type	Contains Codes For	Function in Cell	Translated
Messenger (mRNA)	Sequence of amino acids in protein	Carries the DNA master code to the ribosomes	Yes
Transfer (tRNA)	A cloverleaf tRNA to carry amino acids	Brings amino acids to ribosomes during translation	No
Ribosomal (rRNA)	Several large structural rRNA molecules	Forms the major part of a ribosomes and participates in protein synthesis	No
Micro (miRNA) (siRNA)	Regulatory RNAs	Regulation of gene expression and coiling of chromatin	No
Primer	An RNA that can begin DNA replication	Primes DNA	No
Ribozymes	RNA enzymes, parts of splicer enzymes	Remove introns from other RNAs in eucaryotes	No

Mutations are permanent changes in the genome of a microbe. They may be spontaneous or induced.
Point mutations entail a change in one or a few bases and are categorized based on the effect of the change on the nucleotide(s).
1. Missense mutations: a mutation in which a change in the DNA sequence results in a different amino acid being incorporated into a protein, with varying results. ie: Sickle Cell Anemia they can create a faulty, non functional, (or less functional) protein, they produce a protein which functions in a different manner or cause no significant alteraltion in protein function.
2. Nonsense mutations: a mutation that changes an amino acid-producing codon into a stop codon, leading to premature termination of a protein. ie: Cystic Fibrosis.
3. Silent mutations: a mutation that, because of the degeneracy of the genetic code, results in a nucleotide change in both the DNA and mRNA but not the resultant amino acid and thus, not the protein.
4. Back mutations: a mutation that counteracts an earlier mutation, resulting in the restoration of the original DNA.

Mutations are caused two different ways, by the DNA not pairing up correctly, or by mutagens which are things that damage DNA. With point mutagens there is an alteration of one or more of the bases. Frame-shift mutagens is where there is an insertion or deletion of bases that can interrupt the reading pattern.
Spontaneous mutations are a random change in the DNA that come from errors happening during replication. The cause of these changes are unknown. Induced mutations are caused by being exposed to known mutagens. These known mutagens are physical or chemical and interact with DNA in a negative way. Some physical objects that are able to alter DNA are radiation, UV , X-rays, and high energy gamma rays. Some chemical objects that are able to alter DNA are acridine dyes, agricultural chemicals, and industrial chemicals.
Induced mutations result from exposure to known mutagens, which are primarily physical or chemical agents that interact with DNA in a disruptive nammer. The carefully controlled use of mutagens has provided a useful wy ti induce mutant strains of microorganisms for study.

The Ames Test

The Ames test is a test to determine if a chemical is a mutagen or not. It is based on assuming that any chemical that is a mutagen can turn out to be a carcinogen that causes cancer. A lot of chemicals may not be mutagens but can turn into mutagens once the body has had a chance to metabolize them.
The Ames test uses Salmonella bacteria that are exposed to chemicals. After being exposed, the bacteria is observed for any changes in their growth. One problem with this test is that some of the chemicals that actually do cause cancer do not test positively with the Ames test, and some of the chemicals that test positive do actually cause cancer. It is not always accurate.

Positive and Negative Effects of Mutagens

While some mutations of genes are helpful by causing organisms adapt to changes , others are harmful.


E. coli has single chromosome that have 4,288 genes, imagine only having more in a human cell that is ten times as many into 46 chromosomes.

Questions:

Q&A~~Home Page~~Top of Page

1. ________ is the study of the inheritance, or heredity, of living things.
a. DNA Code
b. Replicon
c. Genetics
d. Translation

2. ______ is the sum total of genetic material of a cell.
a. Chromosome
b. Cell Level
c. DNA Code
d. Genome

3. ________ is the basic unit of DNA structure.
a. DNA Code
b. Replicon
c. Nucleotide
d. Genome

4. _________is a mutation that changes an amino acid-producing codon into a stop codon, leading to premature termination of a protein.
a. Back mutations
b. Silent mutations
c. Missense mutations
d. Nonsense mutations

5. Sickle cell anemia is caused by what kind of mutation?
a. Back Mutation
b. Silent Mutation
c. Nonsense Mutation
d. Missense Mutation

6. Rifamyicins, Tetracyclines and Aminoglycosides are classes of antibiotics that are effective because they:
a. interfere with transcription and translation processes in microorganisms
b. catalyze transcription and translation processes in microorganisms
c. interfere with transcription processes in microorganisms
d. catalyze with translation processes in microorganisms

7. The Ames Test measures:
a. the mutagenicity of chemicals by determining the ability of a chemical to induce mutations in bacteria.
b. the genetic material contained in 'naked' DNA fragments from a donor cell to a competent recipient cell
c. the mutagenicity of organic molecules by determining the ability of molecules to induce mutations in bacteria
d. the severity of Sickle Cell Anemia

8. Cystic Fibrosis is cased by what kind of mutation?
a. Missense Mutation
b. Nonsense Mutation
c. Silent Mutation
d. Back Mutation

9. As a general rule, the template strand on DNA will always begin with?
a. TAC
b. AUG
c. ATG
d. UAC

10. The base pairs are held together primarily by?
a. covalent bonds
b. hydrogen bonds
c. ionic bonds
d. gyrases

11. The replication process includes
a. uncoil the parent DNA molecule
b. unzip the hydrogen bonds between the base pairs
c. synthesize two new strands
d. all of these are correct