Chapter 8 - Microbial Genetics Flashcards
Gene
-a segment of DNA
-produces a functional product (usually a protein or an RNA - mRNA, rRNA, tRNA)
Genome
-the genetic information in a cell
-includes genes and nucleotide sequences
Chromosomes
-structures containing DNA that physically carry hereditary information
-contain the genes
DNA
-macromolecule comprised of repeating units call nucleotides (GCAT)
Antiparallel Nature of DNA
-the sugar in one strand is upside down
-creates stability (hydrogen bonds)
-allows the bases to remain close together
Leading Strand
-Carbon #5 is at the top and is in line with carbon #3 at the bottom
-synthesized continuously in the same direction
Lagging strand
-Carbon #3 is at the top and carbon #5 is in line with it at the bottom
-synthesized discontinuously in fragments of about 1000 nucleotides
Okazaki Fragments
-lagging strand
-the discontinuously synthesized fragments that are later joined to make a continuous strand
Genetic Code
-set of rules that determines how a nucleotide sequence is converted to the amino acid sequence
Importance of Complementary Base Pairs
- linear sequence provides information
- allows for DNA replication during cell division
Genotype
-genetic makeup of an organism
Phenotype
-actual, expressed properties
Central Dogma of DNA
-describes how DNA is transcribed into mRNA
-mRNA is in turn translated into proteins that carry out functions
Base Substitution Mutations
-single DNA base pair is altered
Frameshift Mutations
-DNA base pairs are added or removed from sequence causing a shift in the reading
DNA Replication
-one double stranded DNA molecule is converted to two identical offspring molecules
Semiconservative Replication
-consists of an original strand and a newly synthesized daughter strand
DNA Polymerase
-enzyme that joins the nucleotide to the DNA strand in DNA replication
-adds nucleotides to hydroxyl group at the 3’ end of each nucleic acid
DNA Replication Steps
- parental DNA double helix separates, hydrogen bonds break in response to enzyme action
- hydrogen bonds form between new complementary nucleotides, forming new base pairs
- enzymes catalyze the formation of sugar-phosphate bonds on each resulting daughter strand
Energy Needs
-DNA replication requires a great deal of energy
Step 1: Unzipping (DNA Replication Fork)
-enzyme DNA Helicase unwinds the parental double helix
Step 2: Stabilization (DNA Replication Fork)
-enzyme DNA gyrase stabilizes the unwound parental DNA
-relieves tension
-forms the replication fork (steps 3 and 4)
Step 3: Leading Strand (DNA Replication Fork)
-Enzyme DNA Polymerase is synthesized continuously from the primer
-the proof reader
-used ATP
-results in 5’→3’ (old) and then forms 3’→5’ (new)
Step 4: Lagging Strand (DNA Replication Fork)
-synthesized discontinuously
-Enzyme RNA polymerase (Primase) synthesizes a short RNA primer which is extended by DNA polymerase
-helps DNA polymerase add new nucleotides
Step 5: After step 4 (DNA Replication Fork)
-DNA polymerase digests RNA primer and replaces it with DNA
-Okazaki fragments
-leave a gap
Step 6: Follows step 5 (DNA Replication Fork)
-the gaps are sealed
-DNA ligase joins the discontinuous fragments of the lagging strand
-results in 5’→3’ (old) and then forms 3’→5’ (new)
Bacteria Replication
-replication of DNA is quicker and this allows colonies to appear quickly
-replication moves bidirectionally around the chromosome
-the replication forks meet when replication is completed
Transcription
-copying
-the template to make RNA
-info in DNA is copied as a RNA nucleotide sequence
Translation
-cell uses encoded RNA info to make specific proteins
-decoding the language of nucleic acids converting it to the language of proteins
Ribosomal RNA
-cellular machinery for protein synthesis
-larger in eukaryotes
Messenger RNA
-carries the coded information for making proteins from DNA to ribosomes
-the codon = 3 nucleotides
Transfer RNA
-“box car”
-brings the amino acid to the site of protein synthesis
Ribosomes
-where proteins are synthesized
Prokaryotes
-DNA replication occurs in cytoplasm
-there is no nuclear envelope
Eukaryotes
-DNA replication occurs in the nucleus
-involves RNA splicing
RNA Splicing
-mRNA is processed before translation
-alternating exons (good regions) and introns, introns are removed and exons are left
-the exon chain travels to the cytoplasm where it directs protein synthesis
Steps in Transcription
- RNA polymerase binds to the promotes, DNA unwinds at the beginning of the gene
- RNA is synthesized by complementary base pairing with bases on the template DNA strand
- site of synthesis moves along the DNA, transcribed DNA rewinds
- transcription reaches the terminator
- RNA and RNA polymerase are released and the DNA helix reforms
mRNA Vaccine
-a copied gene froma virus
-won’t affect your genetics
-decoded viral gene
Exons
-regions of DNA that are expressed
Introns
-intervening regions of DNA that do not encode protein
Steps in Translation
- the components needing to begin translation come together
- tRNA carrying the first aa is paired with the start codon on the mRNA, tRNA carrying second aa approaches
- second codon of mRNA pairs with tRNA carrying second aa, first aa joins the second via a peptide bond
- ribosome moves along the mRNA
- second aa joins the third by another peptide bond and the first tRNA is released
- ribosome continues to move along the mRNA and new aa’s are added to the polypeptide chain
- when ribosome reaches a stop codon, the polypeptide is released
- tRNA is released and the ribosome comes apart, released polypeptide forms a new protein
