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BIO 102 > Quiz 6 > Flashcards

Quiz 6 Flashcards

1
Q

timeline of discoveries for DNA structure

A
  • Morgan’s lab: genes located on chromosomes, 2 components (DNA and protein)
  • Griffith (1928): used bacteria to show DNA is genetic material
  • Chargaff (1950): DNA composition varies among species but ratios of purine and pyrimidine bases remains constant
    • hereditary info encoded in DNA found in all cells; directs biochemical, anatomical, physiological, and behavioral traits
  • Watson and Crick (1953): double helical DNA model, images stolen from Franklin and Wilkins
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2
Q

DNA structure

A
  • nucleotide polymer (nitrogenous base, sugar, phosphate group)
  • 3’ and 5’ end
  • bases for Chargaff’s rules about equal A/T and G/C not understood until discovery of double helix
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3
Q

Watson and Crick’s discoveries

A
  • deduced DNA is helical, helix width, spacing of nitrogenous bases, and that DNA has 2 strands in double helix
  • ***models built to conform to chemistry
  • Franklin had already concluded 2 outer sugar-phosphate backbones with nitrogenous bases paired in interior
  • Watson-Crick model found that backbones were antiparallel (subunits run in opposite directions)
  • model explains Chargaff’s rules: purine/pyramidine pairing resulted in uniform width
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4
Q

purines and pyramidines

A

purines: adenine and guanine (2 rings)
pyrimidines: thymine and cytosine (1 ring)

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5
Q

semi-conservative model of replication basics and how did Watson and Crick’s work provide evidence for this?

A
  • Watson and Crick’s discovery of specific base paring suggested a possible copying mechanism (since 2 strands are complementary, each strand acts as a template for building a new strand)
  • parent molecule unwinds and 2 new daughter strands are built based on base-pairing rules
  • “Semi-conservative” because each daughter molecule has one parent strand and one newly made strand (proven using nitrogen isotopes)
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6
Q

where does DNA replication happen?

A

*fast and accurate process with more than a dozen enzymes

  • begins at origins of replication, where 2 DNA strands separate to form a replication bubble (eukaryotic chromosomes may have thousands of these)
  • replication proceeds in both directions from the site until the entire molecule is copied
  • at the end, the replication bubble is a y-shaped replication fork, where new DNA strands elongate
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7
Q

important enzymes before replication

A
  • helicase: untwist double helix at replication fork by breaking hydrogen bonds
  • single-stranded binding proteins: bind to stabilize single-stranded DNA
  • topoisomerase: corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands
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8
Q

how does DNA replication begin?

A
  • primase starts RNA chain at 3’ end using parent DNA as a template (initial nucleotide strand is a short RNA primer 5-10 nucleotides long)
  • works around 50 nucleotides/sec in humans
  • nucleotides are added to the 3’ end of the growing strand (new strand elongates in 5’ –> 3’ direction due to antiparallel structure)
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9
Q

how does antiparallel structure impact DNA replication? (2 strands)

A

2 strands are synthesized differently, replication goes in both directions from the origin of replication

leading strand: synthesized continuously moving towards replication fork (where DNA is unzipped)

lagging strand: synthesized as a series of Okazaki fragments moving away from the replication fork and then shifting back towards it; fragments joined by DNA ligase

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10
Q

DNA replication machine

A

name for the large complex of proteins that participate in DNA replication

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11
Q

how is DNA proofread and repaired? how is it protected?

A
  • DNA polymerases replace incorrect nucleotides
  • repair enzymes correct errors in mismatched base pairing
  • nucleotide excision repair: nuclease cuts out and replaces damages DNA stretches

*DNA is protected by telomeres, special nucleotide sequences at the end of chromosomes that prevent erosion of genes

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12
Q

what damages DNA?

A
  • exposure to harmful chemicals
  • physical agents (x-rays)
  • mutations (although some good)
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13
Q

important enzymes during DNA replication

A
  • DNA polymerase: catalyze elongation of new DNA at replication fork
    * can’t initiate synthesis (requires a primer and template strand) and can only add nucleotides to 3’ end
  • DNA primase: starts RNA chain
  • DNA ligase: joins together Okazaki fragment
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14
Q

makeup of nucleic acids

A
  • polymer “polynucleotides” made up of nucleotide mononers
  • monomers joined by covalent bonds to create backbone
  • include 2 types of nitrogenous bases: purines (adenine, guanine) and pyramidines (cytosine, thymine, uracil)

nucleotides without phosphate: nucleosides

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15
Q

difference between DNA and RNA

A

DNA - 2 polynucleotide chains; antiparallel double helix; complementary base pairing for A/T and G/C
RNA - single polypeptide chains; T replaced by U; complementary base pairing can occur between 2 RNA molecules of parts of the same RNA molecule

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16
Q

types of RNA

A

mRNA (nucleus) - carries genetic info from nucleus to ribosomes in cytoplasm
tRNA (cytoplasm) - carries amino acids to mRNA in ribosomes to form polypeptides
rRNA (ribosomes) - makes up the ribosome, along with proteins

17
Q

what is a gene?

A

region of DNA that can be expressed to produce a final functional product, either a polypeptide or a RNA molecule

18
Q

Beadle and Edward’s mold experiments for the flow of genetic info

A
  • initial “one gene one enzyme” hypothesis
  • changed to “one gene one protein” hypothesis (not all proteins are enzymes)
  • changed to “one gene one polypeptide” hypothesis (some proteins multiple polypeptides)

***proteins are the link between genotype and phenotype!

19
Q

what is gene expression, and its basic steps

A

gene expression: process where DNA directs protein synthesis

  • transcription: synthesis of RNA from DNA using a template strand; producing mRNA
  • translation: synthesis of polypeptides at the ribosomes using mRNA base triplets (codons) to specify amino acid sequence
20
Q

central dogma of gene expression

A

concept that there is a cellular chain of command

DNA - RNA - protein

21
Q

the genetic code

A

universal code for assembling 20 amino acids into proteins using the 4 nucleotide bases in DNA

22
Q

transcription and the role of RNA polymerase

A
  • one of 2 DNA strands provides a template for nucleotide sequence in a RNA transcript
  • RNA polymerase pries DNA apart and hooks in RNA nucleotides
23
Q

transcription initiation

A

formation of the transcription initiation complex: RNA polymerase attaches to the promoter “TATA box” (initial DNA sequence) and transcription factors

24
Q

transcription elongation

A
  • RNA polymerase moves along DNA; untwists helix 10-20 bases at once
  • 40 nucleotides/sec transcribed in eukaryotes
  • several RNA polymerases can transcribe a gene at once!
25
Q

transcription termination

A

pre-mRNA is cleaved from growing RNA chain, polymerase continues transcribing and eventually falls off DNA

26
Q

translation

A
  • mRNA base triplets (codons) specify amino acids to translate mRNA into polypeptides
  • tRNA carries amino acids attached to anticodons that complement mRNA codons
  • occurs at ribosomes in cytoplasm (2 subunits made of proteins and rRNA)
  • enzyme mediated process–all 3 stages require protein factors
27
Q

translation initiation

A
  • mRNA, tRNA, and ribosome come together
  • small subunit moves along mRNA until reaching a start codon (AUG)
  • initiation factors bring in large subunit to make the translation initiation complex
28
Q

translation elongation

A
  • amino acids added by complementary mRNA codon/tRNA anticodon pairings
  • each addition involves elongation factor proteins
29
Q

translation termination

A
  • stop codon in mRNA reaches ribosome; release factor proteins activated
  • ***polypeptide chains often modified after translation to make functional proteins!
30
Q

how does DNA give clues about evolution?

A

linear sequences of nucleotides passed from parents to offspring; 2 closely related species will be more similar in DNA

31
Q

what are mutations? point mutations?

A

mutations: changes in the genetic material of a cell or virus
point mutations: chemical changes in just one base pair of a gene; can lead to the production of an abnormal protein

32
Q

codon

A

codon: small triplet that specifies an addition of one amino acid to the polypeptide (codes for gene to protein)
- 64 codons; 61 code for amino acids and 3 “stop” codons end translation
- redundant (more than one codon may specify a certain amino acid) but not ambiguous (no codon specifies more than one amino acid)
- codons must be read in correct reading frame (correct groupings)

33
Q

transcription unit

A

stretch of DNA being transcribed to synthesize RNA

BIO 102 (14 decks)

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