Chapter 7 Flashcards
The DNA code
discovered in 1953 by James Watson and Francis Crick
Nucleotide
basic unit of DNA;
phosphate, deoxyribose, nitrogenous base
Transcription
1) RNA polymerase binds to the promoter, and DNA unwinds at the beginning of the gene
2) mRNA is synthesized by complementary base pairing
3) the site of synthesis moves along DNA; DNA that has been transcribed rewinds
4) transcription reaches terminator
5) RNA and RNA polymerase are released, and the DNA helix reforms
mRNA
tRNA
rRNA
encodes proteins
moves amino acids
forms the ribosomes
Enzymes in DNA replication
Helicase
Primase
DNA Polymerase III
DNA Polymerase I
Ligase
Gyrase/Topoisomerase
Helicase
unzipping
Primase
synthesis of RNA primer
DNA Polymerase III
Adding bases to DNA strand, proofreading
DNA Polymerase I
Removing primer, closing gaps, removing mismatches
Ligase
binds and repairs DNA
Gyrase/Topoisomerase
supercoiling
DNA Polymerase
in 5’ to 3’ direction
Okazaki fragments
formed during the discontinued lagging strand synthesis
Prokaryotic Transcription
occurs in nucleoid
Bacteria (chracteristics of microbial genomes)
of chromosomes: single (haploid) copies of one or rarely two
type of nucleic acid: circular or linear
no histones, through chromosomes are associated with a small amount of nonhistone protein
Archaea (Characteristics of Microbial Genomes)
of chromosomes: 1 haploid
plasmids: in some cells
circular DNA
histones present
Eukarya (Characteristics of Microbial Genomes)
chromosomes: two or more (typically diploid)
plasminds: in some fungi, algae, and protozoa
linear DNA in nucleus; circular DNA in mitochondria and chloroplasts, and plasmids
First X-Ray picture of DNA
taken in 1952;
created by Rosalind Franklin
Nitrogenous Bases of DNA
guanine, cytosine, adenine, thymine
DNA Ligase
links the Okazaki fragments to form the lagging strand;
catalyzes the formation of bonds between adjacent nucleotides in DNA;
seals nicks in the sugar-phosphate backbone of DNA
Gyrase/Topoisomerase
facilitates supercoiling that allows chromosomes to fit in the space of a bacterial cell
Codons
mRNA is translated in;
three nucleotides
start codon
translation begins at;
AUG
end codon
translation ends at nonsense codons: UAA, UAG, UGA
Anticodon (tRNA);
Codon (mRNA)
codes for a single amino acid
P site (ribosome)
the place where the first tRNA sits
A site (ribosome)
the second codon of the mRNA pairs with the second anticodon of the tRNA, carrying the second amino acid at the A site;
the seond amino acid bonds to the first one by a peptide bond;
this attaches the polypeptide to the tRNA in the P site
E site
last site in the ribosome; releases the tRNA
Trnascription and Translation
5’ to 3’ (DNA)
3’ to 5’ (antisense)
5’ to 3’ (sense)
5’ to 3’ (mRNA; gene copy)
Ionizing Radiation
inducing DNA breaks on a sugar-phophate backbone (caused by X-rays or Y-rays);
can cause a single-strand break or a double-strand break;
has enough energy to break away an electron
Nonionizing Radiation
causes cellular distress through heat generation that eventually leads to the formation of free radicals;
causes atoms to vibrate and heats substances;
does not have enough energy to break away electrons
Nucleotide analogs
disrupt DNA and RNA replication
Frameshift mutagens
result in nonsense mutations
Types of mutations
point mutations
frameshift mutations
Point mutations
most common;
one base pair is affected;
insertions, deletions, and substitutions
Frameshift mutations
nucleotide triplets after a mutation are replaced;
inseritions or deletions
The effect of a chemical mutagen (nitrous acid; NHO2)
chemically modifies adenine to hypoxanthine;
cytosine pairs with hypoxanthine;
resulting mutation: cytosine-guanine base pair
Plasmids
can replicate independently of the bacterial chromosome;
chromosomal fragments must integrate themselves into the bacterial chromosome in order to replicate
Three means of genetic recombination in bacteria
conjugation
transformation
transduction
Conjugation
a mean of genetic recombination in bacteria;
direct contact through pilus;
conjugative proteins replicate the plasmid
Transformation
DNA uptake by a bacteria;
must include the specific expression of proteins that can take up the DNA
Trnasduction
transfer through a virus;
bacteriophage transfers DNA from one bacteria to another;
virus enters; replicates itself;
by mistake replicates bacterial DNA as well;
using its protein transfers DNA to another bacetria
Genetics
the study of heredity;
concerned with
1) how information in nucleic acids is expressed
2) how nucleic acids are duplicated and transmitted to progeny (genotype)
3) these processes account for the characteristics of progeny (phenotype)
Additional DNA
plasmids;
account for nonessential genes;
types: fertility, bacteriocin, virulence, resistance
Bacteriocin
antimicrobial peptide that inhibits or kills another bacteria
The DNA Code
discovered in 1953 by James Watson Francis Crick;
a large molecule;
a nucleic acid;
two strands form a double helix
