TERMS FOR UNIT 2

Question 1

What are the 3 main events of Meiosis I?

Answer 1

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

Question 2

synapsis

Answer 2

The pairing of replicated homologous chromosomes during prophase I of meiosis.

Question 3

crossing over

Answer 3

The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis.

Question 4

tetrad

Answer 4

A paired set of homologous chromosomes, each composed of two sister chromatids. Form during prophase I of meiosis.

Question 5

chiasma

Answer 5

An X-shaped region in each tetrad; represents homologous chromatids that have exchanged genetic material through crossing over during meiosis.

Question 6

complete dominance of 1 allele

Answer 6

Heterozygous phenotype
same as that of homozygous dominant

PP or Pp

Question 7

incomplete dominance of either allele

Answer 7

Heterozygous phenotype
intermediate between the
two homozygous phenotypes

C^R C^R, C^R C^W, or C^W C^W

Question 8

codominace

Answer 8

Both phenotypes
expressed in heterozygotes

I^A I^B

Question 9

multiple alleles

Answer 9

In the population, some
genes have more than two
alleles

I^A, I^B, i

Question 10

Epistasis

Answer 10

The phenotypic expression
of one gene affects the
expression of another gene

Question 11

helicase

Answer 11

unwinds parental double helix @ replication forks

Question 12

single-strand binding protein

Answer 12

binds to and stabilizes single-stranded DNA until it is used as a template

Question 13

topoisomerase

Answer 13

relieves overwinding strain ahead of replication forks by breaking, swivelling and rejoining DNA strands

Question 14

primase

Answer 14

synthesizes RNA primer at 5’ end of leading strand and 3’ end of each Okazaki fragment of lagging strand

Question 15

DNA pol III

Answer 15

Using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to an RNA primer or a preexisting DNA strand

Question 16

DNA pol I

Answer 16

Removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides

Question 17

DNA ligase

Answer 17

Joins Okazaki fragments of lagging strand; on leading strand, joins 3’ end of DNA that replaces primer to rest
of leading strand DNA

Question 18

messenger RNA - mRNA

Answer 18

Carries information specifying amino acid sequences of proteins from DNA to ribosomes

Question 19

transfer RNA - tRNA

Answer 19

Serves as translator molecule in protein synthesis; translates mRNA codons into amino-acids

Question 20

ribosomal RNA - rRNA

Answer 20

Plays catalytic (ribozyme) roles and structural roles in ribosomes

Question 21

primary transcript

Answer 21

Is a precursor to mRNA, rRNA, or tRNA, before being processed; some intron
RNA acts as a ribozyme, catalyzing its own splicing

Question 22

small nuclear RNA - sRNA

Answer 22

Plays structural and catalytic roles in spliceosomes, the complexes of protein and RNA that splice pre-mRNA

Question 23

chromosome

Answer 23

condensed complex of DNA & histone proteins

Question 24

sister chromosomes

Answer 24

while joined 2 sister chromatids make up one chromosome

Question 25

exons & introns

Answer 25

coding regions for expressed DNA

space holders, eventually get spliced out

Question 26

homozygous vs heterozygous

Answer 26

having 2 identical alleles for gene
having 2 different alleles for gene

Question 27

note lecture 6

Question 28

Explain Griffith’s experiments:
rat & bacteria strains

Answer 28

• 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

Question 29

Bacteriophages & radioactive phosphorus & sulfur experiments

Answer 29

• 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

Question 30

Structure of DNA - Xray

Answer 30

• Helical structure
• Sugar-phosphate backbone on the outside
• Uniform width of 2 nm

Question 31

Chargaff’s rules

Answer 31

% of A & T equivalent
% of C & G equivalent

Question 32

Double helix model

Answer 32

• 2 antiparallel strands held together by hydrogen bonding between bases
• base pairing
• DNA uses semiconservative model to replicate

Question 33

RNA polymerase in transcription

Answer 33

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

Question 34

Ribosome role in translation

Answer 34

• 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

Question 35

Overview of transcription

Answer 35

• 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)

Question 36

Overview of translation

Answer 36

• 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

Question 37

trp operon overview

Answer 37

• 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)

Question 38

lac operon overview

Answer 38

• 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

Question 39

restriction enzymes

Answer 39

• Enzymes, naturally present in bacteria, protect against vial infection
• “Cut” DNA at sequence- specific sites

Question 40

gene cloning (define plasmid too)

Answer 40

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

Question 41

PCR

Answer 41

• 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”

Question 42

DNA sequencing

Answer 42

• Human genome project
• Many subsequent full genomes have been sequenced
• Purpose: to find & characterize genes with deleterious phenotypes