TERMS FOR UNIT 2 Flashcards
What are the 3 main events of Meiosis I?
prophase I: homologous pair undergoes synapsis & crossing over between non sister chromatids with subsequent appearance of chiasmata
metaphase I: chromosomes line up as homologous pairs on metaphase plate
anaphase I: homologues seperate from each other, sister chromatids remain joined @ centromere
synapsis
The pairing of replicated homologous chromosomes during prophase I of meiosis.
crossing over
The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis.
tetrad
A paired set of homologous chromosomes, each composed of two sister chromatids. Form during prophase I of meiosis.
chiasma
An X-shaped region in each tetrad; represents homologous chromatids that have exchanged genetic material through crossing over during meiosis.
complete dominance of 1 allele
Heterozygous phenotype
same as that of homozygous dominant
PP or Pp
incomplete dominance of either allele
Heterozygous phenotype
intermediate between the
two homozygous phenotypes
C^R C^R, C^R C^W, or C^W C^W
codominace
Both phenotypes
expressed in heterozygotes
I^A I^B
multiple alleles
In the population, some
genes have more than two
alleles
I^A, I^B, i
Epistasis
The phenotypic expression
of one gene affects the
expression of another gene
helicase
unwinds parental double helix @ replication forks
single-strand binding protein
binds to and stabilizes single-stranded DNA until it is used as a template
topoisomerase
relieves overwinding strain ahead of replication forks by breaking, swivelling and rejoining DNA strands
primase
synthesizes RNA primer at 5’ end of leading strand and 3’ end of each Okazaki fragment of lagging strand
DNA pol III
Using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to an RNA primer or a preexisting DNA strand
DNA pol I
Removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides
DNA ligase
Joins Okazaki fragments of lagging strand; on leading strand, joins 3’ end of DNA that replaces primer to rest
of leading strand DNA
messenger RNA - mRNA
Carries information specifying amino acid sequences of proteins from DNA to ribosomes
transfer RNA - tRNA
Serves as translator molecule in protein synthesis; translates mRNA codons into amino-acids
ribosomal RNA - rRNA
Plays catalytic (ribozyme) roles and structural roles in ribosomes
primary transcript
Is a precursor to mRNA, rRNA, or tRNA, before being processed; some intron
RNA acts as a ribozyme, catalyzing its own splicing
small nuclear RNA - sRNA
Plays structural and catalytic roles in spliceosomes, the complexes of protein and RNA that splice pre-mRNA
chromosome
condensed complex of DNA & histone proteins
sister chromosomes
while joined 2 sister chromatids make up one chromosome
exons & introns
coding regions for expressed DNA
space holders, eventually get spliced out
homozygous vs heterozygous
having 2 identical alleles for gene
having 2 different alleles for gene
note lecture 6
Explain Griffith’s experiments:
rat & bacteria strains
- s strain (smooth, capable of infection), r strain (rough)
- S cells into mouse it dies
- R cells into mouse it lives
- heated S cells so they couldn’t cause infection
- mixed heated S cells & R cells into mouse but it died
- transformation caused by DNA
Bacteriophages & radioactive phosphorus & sulfur experiments
- DNA contains phosphorus but no sulfur.
- Protein contains sulfur but no phosphorus.
- Both sulfur and phosphorus have radioisotopes (355, 32P)
- If only DNA is radioactively labelled, then when you detect radioactivity you can conclude that it is coming from DNA.
- protein was only on outer coating
- DNA being injected into cell by bacteriophages
Structure of DNA - Xray
- Helical structure
- Sugar-phosphate backbone on the outside
- Uniform width of 2 nm
Chargaff’s rules
% of A & T equivalent
% of C & G equivalent
Double helix model
- 2 antiparallel strands held together by hydrogen bonding between bases
- base pairing
- DNA uses semiconservative model to replicate
RNA polymerase in transcription
RNA polymerase attaches to DNA, makes sure the free nucleotide bases match up in complementary way w/ bases on the template strand of DNA (ensures they are lined up, attacted and assembled) then RNA transcript can let them leave nucleus
Ribosome role in translation
- ribosome (organizes translation)
- attaches to mRNA transcript
- reads it and brings in amino acids by tRNAs that have anticodon tag at one and that matches up w/ codons on RNA transcript & at other and there is an amino acid.
- ribosome attaches all these amino acids together
Overview of transcription
- strands of DNA separate along a stretch of the molecule
- free bases attach to corresponding bases on template strand to make mRNA
- newly formed mRNA moves into the cytoplasm (eukaryotes; already in cytoplasm in prokaryotes)
Overview of translation
- ribosome moves along the stand of mRNA three bases at a time
- ribosome brings specific amino acids into place according to the sequence of bases in the mRNA triplets
- at end of the mRNA strand ribosome detaches from the assembled chain of amino acids
- chain folds / subunits combine form the newly completed protein
trp operon overview
- The trp operon is expressed (turned “on”) when tryptophan levels are low and repressed (turned “off”) when they are high.
- The trp operon is regulated by the trp repressor.
- repressible operon (tryptophan binds and prevents RNA polymerase from reading)
lac operon overview
- Lac operon contains genes involved in metabolism.
- The genes are expressed only when lactose is present and glucose is absent.
- The operon is turned on and off in response to the glucose and lactose levels: catabolite activator protein and lac repressor.
- inducible operon
restriction enzymes
- Enzymes, naturally present in bacteria, protect against vial infection
- “Cut” DNA at sequence- specific sites
gene cloning (define plasmid too)
plasmid - circular DNA present in bacteria, used to move genes into it
applications:
- Antibiotic production
move genes into bacteria
- Synthesis of human proteins for therapeutic use ex.: clotting factors, insulin)
- pesticide-resistant crops
PCR
- Make thousands of copies of a piece of DNA
- Check for the presence of a sequence of interest
- Used to verify species
- Identify illegal import/export/food products
- “DNA-barcoding”
DNA sequencing
- Human genome project
- Many subsequent full genomes have been sequenced
- Purpose: to find & characterize genes with deleterious phenotypes
