Micro Exam 2 Flashcards
Define a genome
All genetic material of an organism, including genes that encode proteins, rRNA, tRNA, and small RNAs
Describe the function of a genome
Store and transmit all genetic info necessary for the organism to function, develop, and reproduce
Briefly describe the size and nature (circular) of microbial genomes in comparison to eukaryotic genomes and the human genome
Microbial genomes: typically circular, range from 490-9,400 kb
Eukaryotic genomes: larger, linear, contian more noncoding DNA
Distinguish between monocistronic and polycistronic genes
Monocistronic: one gene, one protein (transcribes individually)
Polycistronic: multiple genes transcribed as a unit (operon)
Define an operon
A set of genes controlled by a single promoter (cluster of genes; 2 or more)
Describe the structure of DNA with respect to its constituent monomers (nucleotides) and its helical structure; what holds the strands together?
Structure:
-Nitrogenous base (ATGC)
-Deoxyribose sugar
-Phosphate group
DNA Strands: antiparallel (5’ –> 3’ and 3’ –> 5’)
Describe the bonds between adjacent nucleotides in a DNA chain
Base pairing
-A-T (2 hydrogen bonds)
-G-C (3 hydrogen bonds)
Describe the hydrogen bonds between complementary bases
Base pairing
-A-T (2 hydrogen bonds)
-G-C (3 hydrogen bonds)
Name the complementary base pairs and compare the two types of pairs with respect to their relative strength and number of H bonds
Base pairing
-A-T (2 hydrogen bonds)
-G-C (3 hydrogen bonds)
Describe the polarity of DNA strands relative to one another in double stranded DNA
Antiparallel
Describe how DNA strand polarity (5’, 3’) gets its name
from the numbering of the carbon atoms in the deoxyribose sugar molecule that makes up the backbone of the strand
Describe the difference between RNA and DNA in terms of the 2’ position and be able to identify this in a diagram
RNA: has an OH on 2’ position
DNA: Has an H on 2’ position (more stable)
Briefly describe supercoiling and its relationship to DNA packing
Supercoiling: DNA helix twists upon itself to fit inside the cell
Describe the difference between positive and negative supercoiling with respect to overwinding or underwinding of the DNA helix
Positive: overwound
Negative: underwound (favored by bacteria for ease)
Identify the electrostatic charge of DNA
Negative because of all the phosphate bonds (each phosphate is negative)
Explain why most bacteria keep their chromosomes in a state of negative supercoiling
Make it easier to unwind
Identify the enzymes that alter the supercoiling state of DNA
Topoisomerases
Briefly explain how these topoisomerase enzymes change the supercoiling state of DNA
temporarily breaking one or both strands of the DNA double helix, allowing a section of DNA to pass through the break, and then rejoining the broken strands
Define DNA replication
Semiconservative, has three steps: initiation, elongation, and termination
Explain what it means for DNA replication to be semiconservative
Each daughter cell gets on original and one new strand
Name the main steps in DNA replication
Initiation: starts at the origin (ori), helicase unwinds DNA
Elongation: DNA polymerase III adds nucleotides in the 5’ –> 3’ direction
Termination: occurs at ter sites, Tus protein halts replication
Identify the loci on DNA where replication begins and ends
Begins at the ori, ends at the ter site
Define the functions of: the initiator protein DnaA; helicase; DNA primase; DNA polymerase III; DNA polymerase I; DNA ligase; RNAse H
-DnaA: initiates replication by melting separate DNA strands
-Helicase: unzips DNA strands
-DNA primase: synthesizes RNA primers
-DNA Polymerase III: main replication enzyme
-DNA Polymerase I: replaces RNA primers with DNA
-DNA Ligase: seals Okazaki fragments (seals nicks on the backbone)
-RNAse H: Digest RNA primers so that they they can be filled with DNA
Explain why DNA primase is needed in replication
DNA polymerase 3 cannot begin making DNA molecule on its own –> it can only elongate existing molecule
Primase makes an RNA primer that can be elongated by DNA polymerase 3