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MCAT Biochem > Chapter 6 > Flashcards

Chapter 6 Flashcards

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MCAT flashcards
1
Q

Nucleoside

A

Five-carbon sugar (pentose) and nitrogenous base

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2
Q

Nucleotide

A

Nucleoside plus 1-3 phosphate groups
Nucleotides linked by phosphodiester bonds

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3
Q

Watson-Crick Model

A

Base-Pairing RUles:
DNA: A pairs with T (2 H bonds)
RNA: A pairs with U (2 H bonds)
C pairs with G (3 H bonds)

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4
Q

Structural Differences DNA vs RNA

A

DNA:
* contains deoxyribose
* contains thymine
* usually double stranded

RNA:
* contains ribose
* contains uracil (excluded from DNA because results from cytosine degradation)
* single stranded

Both proceed in 5’ to 3’ direction

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5
Q

Aromaticity in Nucleic Acids

A

Ex: purines and pyrimidines
Make compounds very stable and unreactive
Stability: important for storing genetic information and avoiding spontaneous mutations

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6
Q

Chargaff’s Rules

A

With RNA, complementarity seen in DNA doesn’t exist
%C doesn’t equal %G, %A doesn’t equal %U

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7
Q

5 Histone Proteins in Eukaryotic Cells

A
  1. H1 (only one not in histone core where DNA wraps to form chromatin)
  2. H2A
  3. H2B
  4. H3
  5. H4
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8
Q

Heterochromatin

A
  • Dense chromatin packing
  • Dark appearance under light microscopy
  • Silent transcriptional activity
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9
Q

Euchromatin

A
  • Uncondensed chromatin packing
  • Light appearance under light microscopy
  • Active transcriptional activity
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10
Q

Telomeres and Centromeres

A

Stay tightly raveled even when rest of DNA is uncondensed due to high GC-content increaing H bonding

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11
Q

Helicase

A

Unwinds DNA double helix
Found in prokaryotes and eukaryotes

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12
Q

Single-stranded DNA-binding Protein

A

Prevents reannealing of DNA double helix during replication
Found in prokaryotes and eukaryotes

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13
Q

Primase

A

Places ~10-nucleotide RNA primer to begin DNA replication
Found in prokaryotes and eukaryotes

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14
Q

DNA Polymerase III

A

Adds nucleotides to growing daughter strand
Found in prokaryotes

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15
Q

DNA Polymerase a

a as in alpha

A

Adds nucleotides to growing daughter strand
Found in eukaryotes

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16
Q

DNA Polymerase I

A

Fills in gaps left behind after RNA primer excision
Found in prokaryotes

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17
Q

RNase H

A

Excises RNA primer
Found in eukaryotes

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18
Q

DNA ligase

A

Joins DNA strands (especially between Okazaki fragments)
Found in prokaryotes and eukaryotes

19
Q

DNA topoisomerases

A

Reduces torsional strain from positive supercoils by introducing nicks in DNA strand
Found in prokaryotes and eukaryotes

20
Q

Lagging Strand

A

More prone to mutations because must constantly start and stop process of DNA replication
Contains many more RNA primers that must be removed and filled in with DNA

21
Q

Telomere

A

Ends of eukaryotic chromosomes
* Contain repetitive sequences of noncoding DNA
* Protect chromosome from losing important genes from incomplete replication of 5’ end of DNA strand

22
Q

Oncogenes (AKA proto-oncogenes)

A

Code for cell cycle-promoting proteins
When mutated, proto-oncogene -> oncogene promoting rapid cell cycling
Like stepping on gas pedal

23
Q

Tumor Suppressor Genes

A

Code for repair/cell cycle-inhibiting proteins
* When mutated, cell cycle allowed to proceed unchecked
Like cutting brakes
* Most likely to result in cancer from inactivation/loss of function mutations

24
Q

DNA Polymerase Distinguishment

A

Parent strand: more heavily methylated
Daughter strand: barely methylated
Can distinguish based off of this during proofreading

25
Q

DNA Polymerase

A

Proofreading
Cell Cycle Phase: S
Key enzymes/genes: DNA polymerase

26
Q

Mismatch Repair

A

Cell Cycle Phase: G2
Key enzymes/genes: MSH2, MLH1 (MutS and MutL in prokaryotes)

27
Q

Nucleotide Excision Repair

A

Corrects lesions that are large enough to distort double helix
Cell Cycle Phase: G1, G2
Key enzymes/genes: Excision endonuclease

28
Q

Base Excision Repair

A

Corrects lesions small enough not to distort double helix
Cell Cycle Phase: G1, G2
Key enzymes/genes: Glycosylase, AP endonuclease

29
Q

Genomic Libraries

A

Include all DNA in organism’s genome including noncoding regions
* Useful for studying DNA in introns, centromeres, or telomeres

30
Q

cDNA Libraries

A

Only include expressed genes from given tissue
* Can be used to express recombinant proteins or to perform gene therapy

cDNA formed from processed mRNA strand by reverse transcription

31
Q

PCR

A

Increases the number of copies of a given DNA sequence
Can be used for a sample containing very few copies of DNA sequence

32
Q

Southern blotting

A

Useful when searching for particular DNA sequence because seperates DNA fragments by length and then probes for sequence of interest

33
Q

Dideoxyribonucleotides

A
  • Lack 3’ -OH group required for DNA strand elongation
  • Once added to growing DNA molecule no more nucleotides can be added because can’t form a bond
34
Q

Transgenic Mouse

A

Gene introduced into germ line/embryonic stem cells to look at effect of that gene
* Best suited for studying effects of dominant alleles

35
Q

Knockout Mouse

A

Gene of interest has been removed instead of added

36
Q

Melting Temperature DNA

A

Temperature where DNA double helix seperates into two single strands (AKA denatures)
* H bond linking base pairs broken
* Higher GC-content higher melting point vs AT

37
Q

Aromatic Rings

A
  • Contain conjugated pi electrons (alternating single and multiple bonds or lone pairs)
  • Won’t exist in carbohydrate ring structures (only single bonds present)
  • Nucleic acids are aromatic heterocycles
  • Proteins have at least one aromatic amino acid usually (ex: tryptophan, phenylalanine, tyrosine)
38
Q

Aromatic

A
  • Cyclic, planar, and conjugated (every atom has at least one unhybridized p-orbital)
  • Contain 4n + 2 pi electrons
  • Most have alternating single and double bonds
  • Can be aromatic with triple bonds (would permit at least one unhybridized p-orbital)
39
Q

Polymerase Chain Reaction

A

Used to clone sequence of DNA using DNA sample (complementary sequence to part of DNA of interest), primer, free nucleotides, and enzymes
* Polymerase from thermus aquaticus used because reaction regulated by thermal cycling (would denature human enzymes)
* Repeated heating/cooling allow enzymes to act specifically and replaces helicase
* Each cycle doubles amount of DNA of interest

40
Q

Restriction Endonucleases

A

Used in gene therapy, southern blotting, and DNA repair

41
Q

Prokaryotic DNA

A
  • Lacks nucleosomes (circular and lacks histone proteins)
  • Replicated by different DNA polymerase (occurs in both but vary in identities)
  • Circular chromsomes
42
Q

Eukaryotic DNA

A
  • Has telomeres
  • DNA organized into chromatin that can condense to form linear chromsomes
43
Q

Gene Sequencing

A

Issues of consent and privacy
* Genetic screening provides information on direct relatives (invasion of privacy in communicating information to family members at risk)
* Fairly accurate
* No significant physical risks
* Not invasive

MCAT Biochem (7 decks)

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