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MOLECULES GENES AND DISEASE > DNA replication and Inheritance of genes > Flashcards

DNA replication and Inheritance of genes Flashcards

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0
Q

What main enzyme carries out DNA replication?

A

-DNA polymerase

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1
Q

Why does DNA need to be replicated?

A

-In order to produce an identical daughter cells

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2
Q

What does helicase do?

A

-Unwinds the DNA molecule for replication

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3
Q

What is the substrate of DNA replication?

A

-dNTPs

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4
Q

In which direction does chain elongation occur?

A

-Growth is in 5’->3’ direction

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5
Q

At what stage of the cell cycle does DNA replication occur?

A

-S phase

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6
Q

Why is DNA replication described as semi-conservative?

A

-One parent strand in each daughter cell

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7
Q

How is initiation of DNA replication defined?

A

-By origins of replication

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8
Q

What is the end product of DNA replication?

A

-Two DNA molecules

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9
Q

What are the two strands named during DNA replication?

A
  • Leading strand

- Lagging strand

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10
Q

How are the two strands synthesised (in what manner?)

A
  • Leading strand is synthesised continually

- lagging strand is synthesised discontinually

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11
Q

Why is the lagging strand synthesised discontinuously?

A

-The lagging strand is synthesised discontinually because elongation occurs in a 5’->3’ drection. As helicase unwinds, DNA pol binds nearest the site where DNA is still wound and works backwards on itself as this is the 5’-3’ direction of the new strand. As helicase unwinds some more and DNApol has finished that segment, it unbinds and rebinds further down the strand

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12
Q

What does the lagging stand produce and what enzyme is needed?

A
  • Okazaki fragments

- Ligase to join the fragments together

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13
Q

What two bonds are involved in the addition of a dNTP and where?

A
  • Phosphodiester bond between a phosphate of one dNTP and the -OH at C3
  • Hydrogen bonds between the complementary nitrogen bases
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14
Q

Describe cell cycle

A
  • G0= resting phase (non-dividing cells; some cells can pass to G1)
  • G1= cell content replication
  • S= DNA replication
  • G2= double check and repair
  • 0=interphase
  • M= cell division
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15
Q

Where are the two cell cycle checkpoints in cell cycle?

A

-Between G1:S and G2:M

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16
Q

Describe initiation of DNA replication

A
  • Helicase unwinds DNA creating replication fork
  • Primase binds to the strand to be replicated, adding a primer to the strand and recruits DNA pol
  • Simultaneous recruitment of specific proteins
  • DNA pol replication begins
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17
Q

Describe the process of elongation during DNA replication

A
  • Helicase unwinds DNA

- Primer and DNApol bind and move towards the 5’ ends of the strands, adding complementary dNTPs

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18
Q

Where will the primer be located in the new strands of DNA?

A

-At the start at the 5’ end

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19
Q

Describe termination of DNA replication

A
  • There are several DNApol on one DNA molecule due to there being multiple origins of replication, and thus multiple replication forks
  • When replication forks meet, DNApol unbinds and elongation stops
  • The separate stand segments produced by the various replication forks are fused together by DNA ligase to produce one continuous molecule of DNA
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20
Q

What is the end result of DNA replication

A

-Pair of sister chromatids connected by a centromere -> still called a chromosome

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21
Q

What determines the position of the centromere?

A

-It is sequence dependant

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22
Q

In what cells is mitosis used and what is its purpose?

A
  • In somatic cell lines

- To produce 2 identical daughter cells

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23
Q

At what stage of the cell cycle does mitosis occur and which processes have already happened?

A
  • Happens in M

- G1, S and G2 already occured

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24
Q

Name locations where mitosis is necessary?

A
  • Epidermis
  • Mucosae
  • Bone marrow
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25
Q

Describe prophase of mitosis?

A
  • Breakdown of nuclear membrane
  • Spindle fibres and centrioles appear
  • Chromosomes condense
  • C46, SC92
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26
Q

Describe prometaphase

A
  • Spindle fibres attach to chromosomes

- Chromosomes condense

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27
Q

Describe metaphase in mitosis

A

-Chromosomes align by random assortment (In any order) at the metaphase plate

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28
Q

Describe anaphase in mitosis

A
  • Centromeres divide

- Sister chromatids move to opposite poles (Each cell receives a mC1 and a pC1; they are identical)

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29
Q

Describe telophase in mitosis

A
  • Nuclear membrane reforms
  • Chromosomes decondense (euchromatin)
  • Spindle fibres disappear
  • Cleavage furrow appears
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30
Q

Describe cytokinesis

A
  • Cytoplasm divides
  • Parent cell becomes two daughter cells
  • C46, SC46
31
Q

What is a kinetochore?

A

-Protein complex structure which binds the centromere to the spindle fibres

32
Q

What is the purpose of meiosis?

A

-To produce 4 non-identical gametes, i.e sperm and egg

33
Q

What are the two main differences between mitosis and meiosis?

A
  • Meiosis has one round of replication but then two rounds of division
  • Meiosis produces cells with haploid chromosome number
34
Q

Describe prophase I of meiosis

A
  • Disintegration of nuclear membrane
  • Spindle fibres appear
  • Chromosomes condense
  • C46, SC92
35
Q

What is crossing over?

A

-The exchange of maternal chromosome material with paternal chromosome material between non-sister chromatids

36
Q

What are non-sister chromatids?

A

-Chromatids of non-homologous pairs within the same tetrad, eg mC1 and pC1

37
Q

What is the result of crossing over?

A

-Results in chromosomes with mixed genetic material

38
Q

Describe metaphase I of meiosis

A

-Independant assortment of chromosomes at the metaphase plate
ie
-Sister chromatids find there homologous pair and form a tetrad at the metaphase plate
-Crossing over occurs

39
Q

Describe independent assortment in metaphase I of meiosis

A

-Homologous pairs of chromosomes find each other and line up to form a tetrad, i.e. mC1 finds pC1 and line up

40
Q

Describe anaphase I of meiosis

A
  • Tetrad divides as spindle fibres retract (no splitting of centromeres)
  • One daughter cell gets mC1 and other gets pC1 and so on
41
Q

Describe telophase I

A
  • Nuclear membrane reforms
  • Spindle fibres disappear
  • Cleavage furrow
  • 2 non-identical daughter cells produced
  • C23, SC46
42
Q

Describe prophase II of meiosis

A
  • Nuclear membrane disintegrates
  • Spindle fibres appear
  • C23, SC46
43
Q

Describe metaphase II of meiosis

A

-Chromosomes with sister chromatids randomly assort on the metaphase plate

44
Q

Describe anaphase II of meiosis

A
  • Spindle fibres contract
  • Sister chromatids separate
  • Each cell will only be haploid
  • They will be non-identical due to crossing over of tetrads
45
Q

Describe telophase II of meiosis

A
  • Nuclear membrane reforms
  • Chromosomes decondense to exhibit euchromatin
  • Spibdle fibres disappear
  • Cell Division
  • C23 SC23
46
Q

What are the consequences of meiosis?

A
  • Generates genetic diversity through independent assortment and crossing over
  • Maintains the chromosome number as two haploid cells fuse during fertilisation
47
Q

How long does spermatogenesis take?

A

-approx. 48 days from spermatid to mature sperm

48
Q

What is different about oogenesis?

A

-Only one gamete becomes a mature ovum, the rest become polar bodies

49
Q

What happens if crossing over does not occur?

A
  • Crossing over is essential
  • Without crossing over sister chromatids will not separate
  • Produces empty gametes and some with double genetic info
50
Q

Faulty meiosis is the leading cause of…

A

…mental retardation

51
Q

Define genotype?

A

-Genetic make up of an individual as either a whole, or for one specific gene locus

52
Q

Define phenotype

A

-All the observable characteristics of an individual or the observable trait as a result of the genotype at one (or more) specific loci

53
Q

How can environmental factors affect the phenotype?

A

-Environmental factors can influence and overcome the genotype and therefore alter the natural phenotype

54
Q

Define gene

A

-A unit of hereditary; a length of DNA on a chromosome which codes for a protein

55
Q

Define allele

A

-An alternate form/copy of a gene

56
Q

List some environmental factors which can effect genotype/phenotype

A
  • Radiation
  • Mutagens
  • Chemicals which effect growth
  • Diet
  • Lifestyle
  • Infection
57
Q

What are the 5 different patterns of inheritance?

A
  • Autosomal recessive
  • Autosomal dominant
  • X-linked recessive
  • X-linked dominant
  • Y-linked
58
Q

Define homozygous

A

-Two alleles of the gene are the same (homozygote)

59
Q

Define heterozygous

A

-Two different alleles of the same gene (heterozygote)

60
Q

Define hemizygous

A

-Only one allele of the gene on the X chromosome (males only)

61
Q

Define dominant allele

A

-The allele which determines the phenotype

62
Q

Define recessive

A

-Th non-dominant allele

63
Q

Describe autosomal recessive inheritance, give an example

A
  • Heterozygotes are not effected but are said to be carriers
  • males/females affected equally
  • Disease can appear to skip generations
  • Two homozygotes will have an affected offspring
  • Cystic Fibrosis
64
Q

What is the chance of two heterozygotes for an autosomal recessive trait having an affected offspring?

A

-25%

65
Q

Describe autosomal dominant inheritance, and give an example

A
  • Heterozygotes will be affect
  • Males/females affected equally
  • Rarely found in homozygous state -> disease usually too severe to take to term
  • Every affected individual will have at least 1 affected parent
  • Disease can not skip a generation
  • Huntingtons disease
66
Q

What are the chances of two heterozygotes for a autosomal dominant trait having an affected offspring?

A

75%

67
Q

Describe X-linked recessive inheritance, and provide an example

A
  • Homozygous females affected
  • All males affected
  • Males affected more than females
  • Every affected female will have an affected father and at least a carrier mother
  • Affected males can not give trait to sons
  • Unaffected daughters of affected males will be carriers
  • Haemophilia A
68
Q

What is the chance of a heterozygous female for an X-linked recessive trait producing an affected son?

A

-50%

69
Q

Describe X-Linked dominant inheritance

A
  • All heterozygotes affected
  • Males/females affected equally
  • Affected males have an affected mother
  • affected daughter has at least one affected parent
70
Q

Describe co-dominance inheritance using an example

A
  • Alleles work together to produce phenotype
  • ABO blood typing (Isoglutamine genes code for glycoproteins on RBC surface)
  • I has three alleles (A, B and O)
  • IA dominant over O
  • IB dominant over O
  • Neither IA or IB are dominant over each other; they are codominant
71
Q

What is complementation, provide an example

A
  • When two different genes complement each other to produce the final phenotype
  • Albinism
  • Recessive inheritance
  • The two genes both have two alleles
  • Complement offspring will be heterozygous for both alleles
  • One genotype complements for faulty genotype of the other
72
Q

When are genes said to be linked?

A

When they are on the same chromosome

73
Q

Why do linked genes not show independent assortment?

A

-genes can not go into different gametes as they are on the same chromosome, especially if they are close together as this reduced the chance of crossing over

74
Q

What is recombination?

A

-The process by which two genes exchange information resulting in the production of a new combination of alleles

75
Q

What is recombination frequency and how is it calculated?

A
  • The frequency with which a single chromosome cross over will take place between 2 genes, dependant on the distance between those genes
  • X-linked only use males because you can be 100% sure that their phenotype is correct
  • Look at the first recombinant generation and count the males affected in that generation and every affected generation after
  • Count the number of recombination events in the first recombinant generation
  • That is the frequency
  • Hint: Recombination is usually identified in X-linked when a male has both disease traits but the father is normal

MOLECULES GENES AND DISEASE (12 decks)

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