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Genetics > DNA Structure and Replication > Flashcards

DNA Structure and Replication Flashcards

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Biology 101 flashcards
1
Q

Genes

Locus

Alleles

A
  • segments of DNA that encode proteins by serving as template for mRNA molecules
  • precise location of ea gene on a chromosome
  • identical genes on pairs of chromosomes
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2
Q

Centromere

Telomere

A

-where spindle fibers attach during chromosome segregation

  • specialized structures that maintain integrity of chromosomes at their ends
  • Define ends of all human chromosomes
  • Usually contain multiple tandem repeats of TTAGGG sequence
  • Important for stability and replication of chromosomes
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3
Q

Nucleosome

A
  • Basic unit of chromatin
  • ~147 Bps and a histone octomer (octomer has 2 of ea H2A H2B H3 H4 proteins)
  • Individual nucleosomes connected by linker DNA (~50 Bps bound by H1 histone)
  • can be remodeled by remodeling complexes
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4
Q

Nucleotide

A
  • nitrogenous base + deoxyribose sugar + a phosphate

- Purines (AG) and pyrimidines (CT or U if RNA)

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5
Q

Bonds in DNA molecules

A
  • Glycosidic bonds- link bases to sugars
  • Phosphodiester bonds- link adjacent nucleotides together; covalent; join 3’ carbon of one deoxyribose or ribose to 5’ carbon of the next (SO KEEP EA SEP STRAND INTACT)
  • Hydrogen bonds- holds 2 strands of DNA together
    • A-T pairs held together by 2 H+ bonds
    • C-G pairs held together by 3 H+ bonds
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6
Q

Watson Crick DNA Structure

A

dbl helix/R handed of ~10 bp /turn

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7
Q

Sense v Antisense Strands

A
  • Sense strand- DNA strand w/in gene whose sequences is same as that of mRNA copy that is translated into protein
  • Antisense strand- complementary to sense strand
    • **Which strand is sense and which is antisense can vary in diff parts of chromosome
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8
Q

DNA replication and Cell Cycle

A

Interphase (G1 S G2) and mitosis (M)
-Chromosome contains 1 DNA dbl helix from anaphase of mitosis -> DNA duplication in S phase (2C)

    • DNA duplicates in S phase
      • From this point until end of metaphase the chromosome consists of 2 chromatids (ea containing DNA duplex) (4C)
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9
Q

DNA Helicase

A

Unwinds DNA by breaking H+ bonds

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10
Q

Features of DNA Replication

A
  • Origins of replication (initiator proteins bind to sequences w/in these)
  • Semi-conservative
  • Semi-continuous (leading strand is synthesized continuously starting from origin of replication while lagging strand is synthesized as small Okazaki fragments)
  • Bi-directional
  • Replication Fork (Region b/n unwound parental duplex and newly replicated daughter duplexes)
  • Low frequency of error
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11
Q

Replication Bubble

A

formed by replication fork initiation

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12
Q

DNA Polymerases General Function

A

Enzymes that catalyze addition of deoxyribonucleoside to free 3’ hydroxyl group of growing DNA strand

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13
Q

DNA Ligases

A

ligases connect the Okazaki fragments

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14
Q

DNA Primase

A
  • Synthesizes small RNA primers used as primers for synthesis of short initiator DNA (both leading and lagging strands)
    • Leading strand needs 1 RNA primer while lagging strand needs multiple RNA primers
  • Associated w/ alpha DNA polymerase
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15
Q

Steps of DNA Replication

A
  • 1-Primase subunit of DNA polymerase alpha complex synthesizes short RNA primer (7-12 nuc long)
  • 2- Then DNA polymerase portion of gamma polymerase synthesizes about 30 nuc of DNA
  • 3- epsilon polymerase takes over for leading strand AND delta polymerase takes over for lagging strand
  • 4- RNA primers removed by RNase H activity
  • 5- Gap in strand is filled by DNA polymerase delta or epsilon
  • 6- DNA sealed by DNA ligase
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16
Q

Topoisomerases

A
  • Bind DNA ahead of replication fork, leave phosphate backbone allowing 2 strands to unwind; then reseal DNA
  • *Inhibitors of topoisomerases used as anti-bacterial and anti-cancer agents
17
Q

Telomerase

A
  • Telomerase extends the TG-rich strand of telomeres by DNA synthesis using internal RNA template
  • Ribonucleoprotein complex (reverse transcriptase)
  • Important role in cell aging and cancer development
  • Present in embryonic stem cells and germ cells but most normal somatic cells lack telomerase
  • Telomerase activated in many types of cancer cells (potential target for anti tumor drugs)
18
Q

SSBs

A

Single-strand binding proteins

Hold replication fork open in DNA replication

Genetics (30 decks)

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