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MCAT Biochemistry > DNA Replication, Mitosis, and Mutations > Flashcards

DNA Replication, Mitosis, and Mutations Flashcards

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MCAT flashcards
1
Q

Cell Division in human cells

A

Not all cell types undergo cell division including fully differentiated cells (e.g. neurons)

Cells with short lifespans have progenitor cells to routinely replace them (skin cells and intestinal cells)

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2
Q

DNA replication

A

Synthesis of an exact copy of the genome to be included in the newly created cell after division

Takes place during S phase of interphase portion of cell cycle

Semiconservative, as resulting DNA double helix has one new and one old strand

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3
Q

Replisome

A

Group of proteins that governs mechanism of DNA replication
Attaches to the chromosome at origin of replication, marked by epigenetic factors
Creates a replication fork that moves along chromosome over course of replication
DNA helicase, DNA polymerase, primase, DNA ligase

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4
Q

DNA Helicase

A

Enzyme in replisome which unwinds the double helix, separating the two DNA strands

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5
Q

DNA polymerase

A

Enzyme in replisome which synthesizes new DNA strands by pairing complementary free-floating deoxynucleotides which sequence of nucleotides on exposed DNA strand

Reads parental strand in 3’ to 5’ direction, can only add nucleotides to existing strand

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6
Q

Primase

A

RNA polymerase that creates an RNA primer of around 10 ribonucleotides to initiate replication

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7
Q

Single Strand Binding Tetramer Proteins

A

AKA helix destabilizer proteins or SSB

stabilizes the looped around lagging strand to prevent it from folding back on itself

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8
Q

Leading Strand

A

Continuously synthesized strand in DNA replication from which the direction of DNA polymerase movement (3’ to 5’) on the template strand is the same as the direction of the replication fork across the DNA helix

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9
Q

Lagging Strand

A

Strand synthesized by series of disconnected strands (Okazaki fragments) during DNA replication.
This is due to the direction of movement of the replication fork being 5’ to 3’ on the template strand. DNA polymerase is always moving 3’ to 5’ on template strand, so has to create discrete fragements

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10
Q

Okazaki Fragments

A

Series of disconnected fragments in DNA replication produced on lagging strand
Around 200 nucleotides long in Eukaryotes and 1000-2000 long in Prokaryotes

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11
Q

DNA Ligase

A

Joins together adjacent Okazaki fragments on lagging strand in DNA replication

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12
Q

RNAase H

A

Removes RNA primers in DNA replication after DNA strands are synthesized

Gaps are then filled in by DNA polymerase

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13
Q

Telomeres

A

Repeated six nucleotide units from 100 to 1000 units long that protect the ends of chromosomes

Can become shortened through by repeated rounds of replication- linked to aging and disease

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14
Q

Telomerase

A

Catalyzes lengthening of telomeres in Eukaryotic organisms by adding many 5’ TTAGGG 3’ nucleotide sequences to ends of chromosomes

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15
Q

Five main steps of DNA Replications

A
  1. Helicase unzips double helix
  2. RNA polymerase (primase) binds a primer
  3. DNA polymerase assembles leading and lagging strands
  4. RNAase H removes primers
  5. DNA ligase joins Okazaki fragments together
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16
Q

How does DNA polymerase function to correct errors in DNA replication?

A

One of the subunits in DNA polymerase is an exonuclease that removes nucleotides from the strand

Automatically proofreads each new strand during synthesis and repairs mismatched nucleotides
1 out of every 10^9-10^11 base pairs is incorrect

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17
Q

Mitosis

A

Process by which two cells are created that are identical to both each other and to original cell

Occurs in succession with DNA replication

Nuclear division without genetic change
Four main stages: prophase, metaphase, anaphase, telophase

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18
Q

Prophase

A

Condensation of chromatin into chromosomes
Tightly coiled chromosomes down-regulates gene expression during mitosis
Centrioles move to opposite poles of cell
Nucleolus and then nucleus disappear
Spindle apparatus begins to form

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19
Q

Sister Chromatids

A

Two identical copies of duplicated chromosomes

Joined near centers, called centromeres

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20
Q

Centrosomes

A

Structure in which the centrioles are located in the cell

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21
Q

Spindle Apparatus

A

Consists of asters (microtubules radiating from centrioles), kinetochore microtubules growing from centromeres, and spindle microtubules connecting the two centrioles

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22
Q

Kinetochore

A

Structure of protein and DNA located at centromere of joined chromatids of each chromosome

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23
Q

Metaphase

A

Chromosomes align along the equator of the cell

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24
Q

Anaphase

A

Sister chromatids split at attaching centromeres and segregate to opposite sides of cell
Kinetochore microtubules shorten to pull sister chromatids apart (disjunction)

25
Q

Cytokinesis

A

Actual separation of cellular cytoplasm due to constriction of microfilaments around center of cell

Can happen at end of anaphase or in telphase

26
Q

Telophase

A

Nuclear membrane reforms, followed by reformation of nucleolus
Chromosomes de-condense (difficult to see under light microscope)

Cytokinesis finishes

27
Q

Mutation

A

Any alteration in the genome that is not due to genetic recombination
Source of genetic variation within populations
- Evolution
Spontaneous or Induced

28
Q

Spontaneous Mutation

A

Mutations that occur due to random errors in the natural process of replication and genetic recombination

29
Q

Induced Mutations

A

Mutations that occur due to physical or chemical agents called mutagens
- cause damage to DNA and increase frequency of mutations above baseline error rates

30
Q

Effect of Mutation

A

Advantageous, deleterious, or no effect at all

Can occur at the level of the nucleotide or the level of the chromosome

31
Q

Gene mutation

A

Alteration in the sequence of DNA nucleotides in a single gene

32
Q

Chromosomal Mutation

A

Structure of chromosome is changed

33
Q

Somatic Mutation

A

Mutation in somatic cell

Somatic mutation of a single cell may have very little effect on an organism with millions of cells

34
Q

Point Mutation

A

Mutation that changes a single nucleotide in a double strand of DNA

Includes a base substitution mutation, addition mutation, and deletion mutation

35
Q

Base substitution mutation

A

One nucleotide is swapped for another during DNA replication
Transition mutation: swaps a purine for other purine or pyrimidine for other pyrimidine
Transversion mutation: exchanges a purine for a pyrimidine or vice versa

36
Q

Addition mutations

A

Inserting a new nucleotide into the sequence

Can have profound effect on function of gene

37
Q

Neutral Mutation

A

Has no effect on organism’s fitness

Could change amino acid without a change to protein’s function, or could change codon without changing resultant amino acid (silent mutation)

38
Q

Silent mutation

A

A base pair change without a change to the resultant amino acid

Possible through wobble in genetic code

39
Q

Missense Mutation

A

Base substitution changes a codon which results in the translation of a different amino acid

Can be neutral, or can significantly change polypeptide’s function

40
Q

Nonsense Mutation

A

Change to the nucleotide sequence creates a stop codon where none previously existed

Usually create a truncated, non-functional protein

Serious consequences

41
Q

Frameshift Mutation

A

Deletions or additions occur in multiples other than three

This changes the reading frame of the code, which means that the entire sequence after the mutation will be shifted
Most often results in a completely non-functional protein

42
Q

Structural Mutations

A

Point mutation

  • base substitution mutation
  • addition mutation
  • deletion mutation
43
Q

Functional Mutation

A
  • Silent mutations
  • Missense mutations
  • Nonsense mutations
  • Frameshift mutations
44
Q

Chromosomal Mutations

A

Structural changes may occur to a chromosome in the form of:

  • deletions
  • duplications
  • translocations
  • inversions
45
Q

Chromosomal Deletions

A

Portion of chromosome breaks off or is lost during homologous recombination or crossing over

Serious consequences for organism

46
Q

Chromosomal duplications

A

DNA fragment breaks free of one chromosome and incorporates into a homologous chromosome

Gene duplication/amplification: can increase amount of a gene’s product
Aneuploidy: entire chromosome duplicated
Polyploidy: set of chromosomes duplicated

47
Q

Chromosomal Translocation

A

Segment of DNA from one chromosome is exchanged for a segment of DNA on another chromosome (reciprocal translocation)

48
Q

Chromosomal Inversions

A

Orientation of a section of DNA on a chromosome is inverted

49
Q

Transposition

A

A process in Eukaryotic and Prokaryotic cells in which DNA segments called transposable elements or transposons can excise themselves from a chromosome and reinsert themselves at another location
Mechanism by which a somatic cell of multicellular organism can alter its genetic makeup without meiosis

50
Q

What are some causes of DNA damage?

A
  1. Oxidation by free radicals
  2. Errors in DNA replication
  3. Exposure to environmental carcinogens
51
Q

Effect of Ultraviolet light on DNA

A

Covalently links two neighboring thymine bases together
- causes kink in DNA strand

DNA repair enzymes can cleave cross-links

52
Q

How are oxidized nucleotide bases repaired?

A

Can be corrected through excision repair in which damaged nucleotides are removed and replaced

53
Q

Cancer

A

Unrestrained and uncontrolled growth of cells that results when the regulation of the cell cycle has gone awry

54
Q

Proto-oncogenes

A

Genes that stimulate normal growth in human cells

Can be converted to oncogenes by mutagens such as UV radiation or chemicals, or random mutations
Oncogenes: genes that cause cancer

55
Q

Carcinogens

A

Mutagens that can cause cancer

56
Q

Tumor suppressor genes

A

Genes that help regulate normal cell growth

Can be checkpoints during the cell cycle

  • retinblastoma (Rb)
  • p53 proteins
57
Q

Deletion mutation

A

Deleting a nucleotide from the sequence

Can have profound effects on function of gene

58
Q

Replication Units

A

AKA replicons
Discrete segments of DNA replication in Eukaryotic cells

Eukaryotic chromosomes contain multiple origins of replication due to long length of chromosomes

59
Q

What direction does DNA replication proceed from replication fork?

A

DNA replication is a bidirectional process, because replisomes proceed in opposite directions from origin of replication

MCAT Biochemistry (11 decks)

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