Exam 3: Microbial Genetics I- Structures and Replication Flashcards
What is genetics? How does it relate to other units we have studied in this course?
Genetics is the study of inheritance. Genes code for all the enzymes and proteins that we have discussed previously. Everything else occurred because it was coded in the genes.
At what levels is genetics studied? Give a specific example of each.
Subcellular (molecular) level- looking at the genes, how they work.
Individual- specific genes of an individual including mutations.
Population- trends within a population, evaluating evolution.
Describe the structure of a single strand of DNA.
Backbone is alternating sugars and phosphates. Nitrogenous bases protrude from sugars. Nitrogenous bases interact with each other via hydrogen bonds. A-T and G-C.
Describe the specific interactions between the two strands of a double-stranded DNA molecule.
The two strands are connected via hydrogen bonds resulting in a 3D double helix. Base sequence of the first strand dictates the base sequence of the second strand. The second strand does not encode for additional information.
The two strands of a double helix are antiparallel. Explain the meaning of this term.
parallel but “pointing” in opposite directions. 3’ to 5’ and 5’ to 3’, determined by counting the carbons on the end nitrogenous base, the open carbon determines the name.
Describe the structure of the typical bacterial genome. In what ways do different bacterial genomes often differ from each other?
Circular, one chromosome, haploid (generally but not always), not membrane bound, consists of DNA and associated proteins.
Describe the nature of a typical eukaryotic genome.
Linear, multiple chromosomes, DNA and associated proteins, often two copies of each chromosome (diploid), membrane bound in a nucleus.
In what ways is a typical bacterial chromosome like a eukaryotic chromosome? In what ways are they different?
Both consist of DNA and associated with proteins.
Bacteria are circular while the eukaryotic chromosome is linear.
Bacteria have one chromosome, eukaryotes multiple chromosomes.
Bacteria haploid (generally), eukaryotic chromosomes often diploid.
Bacteria localized in nucleoid not true membrane bound. While eukaryotes have a nucleus.
Bacteria are generally haploid, whereas eukaryotes are often diploid. How does the haploid nature of bacteria (or even of haploid eukaryotes) make studying their genetics easier?
With only a single chromosome vs two copies they are unable to mask mutations. In diploids if there is a mutation in one gene there is another normally functional copy that gets used for expression so phenotypic results are not seen.
What are histones? How does eukaryotic DNA interact with histones? In what way is this interaction important?
Histones are a type of protein associated with eukaryotic DNA. The DNA is wrapped around the histone proteins to form nucleosomes. Purpose is to help give chromosomes their shape, and help control the activity of genes.
Is all eukaryotic DNA in the nucleus? Explain.
No, in certain endosymbiotic organelles there is extracellular DNA. For example the mitochondria, chloroplasts, and some other organelles contain DNA. These organelles have bacterial origins and contain circular chromosomes.
What is a plasmid? In what ways are bacterial plasmid like typical bacterial chromosomes? In what ways are they different?
Small, circular, double-stranded DNA molecule that is distinct from a cell’s chromosomal DNA. 1-10% the size of a normal chromosome. Has the ability to direct its own replication. Often possess genes for one or more cellular traits but are not essential for normal metabolism.
Are plasmids essential for bacteria? Can they be helpful? Explain the difference between your answers to these two questions.
Not essential, but often helpful for example they can hold genes for antibiotic resistance.
Do eukaryotes ever contain plasmids? Explain.
Some possess plasmids, for example some fungi, algae, and protozoa. Encoded genes involved solely in plasmid replication.
Describe at least three different groups of plasmids, differing in the nature of the products they encode.
Fertility (F) plasmids: carry instructions for conjugation, a type of gene transfer.
Resistance (R) plasmids: Carry genes for providing resistance to antimicrobial agents.
Bacteriocin plasmids: Carry genes for protein toxins called bacteriocins, which can kill competitors.
Virulence plasmids: carry instructions for pathogenic features.
In a single sentence and in basic terms, describe the semi-conservative nature of DNA.
One DNA separates and complementary strands of each are built. Results in two daughter strands each containing one strand from the original strand.
In a single sentence and in basic terms, describe the semi-conservative nature of DNA.
One DNA separates and complementary strands of each are built. Results in two daughter strands each containing one strand from the original strand.
Is DNA synthesis an anabolic or a catabolic process? Explain.
Anabolic because it is an energy requiring process to build something big.
In what form are the deoxyribonucleotides supplied for DNA synthesis? Why is this form important?
Supplied as triphosphates which all possess 3 linked phosphate groups. dATP, dTTP, dGTP, and dCTP. When these groups are broken during polymerization they provide energy needed for the process.
What is an origin of replication?
Enzyme helicase locally unzips the DNA strand by breaking hydrogen bonds. Single strands are separated producing a replication bubble with two replication forks one on either end. Helicase also removes proteins already bound to DNA but other proteins stabilize the separated strands.
