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Biology > TH- DNA and inheritance > Flashcards

TH- DNA and inheritance Flashcards

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1
Q

What is transformation according to Griffith?

A

a change in genotype and phenotype due to the assimilation of external DNA by a cell

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2
Q

What experiment lead Griffith to observe transformation?

A

he killed the pathogenic bacteria with heat and then mixed the cell remains with living bacteria of the nonpathogenic strain, some of the living cells become pathogenic

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3
Q

What are bacteriophages?

A

viruses that infect bacteria

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4
Q

Describe Hershey and Chase’s experiment that proved DNA is a genetic material (8)

A
  • 2 samples of phages were grown, one was grown in radioactive isotope of Phosphorus that tagged the DNA and another was grown in radioactive isotope of Sulfur which tagged the protein
  • both samples were mixed with bacteria allowing them to infect the bacterial cells
  • The samples were then mixed in a blender to free the of the phage parts outside the cell
  • then the mixture was centrifuged to separate the bacteria into a pellet at the bottom and the free phages and phage parts, which are lighter, remained suspended in the liquid above.
  • both the samples radioactivity was measured
  • the protein was found in the liquid and the DNA in the pellet
  • this suggests that the DNA entered the bacterial cell
  • hence DNA was carrying the genetic material as it was responsible in entering the cell and reprogramming it to produce viruses
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5
Q

What are Chargaff’s rules? (2)

A

(1) DNA base composition varies between species

(2) for each species, the percentages of A = T bases and G = C

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6
Q

Describe the structure of an individual DNA molecule

A

a deoxyribose sugar bonds to a phosphate group on its carbon 5 and a nitrohenous base on its carbon 1

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7
Q

Describe the structure of DNA strands

A
  • via dehydration reaction phosphate on carbon 5 covalently bonds with Carbon 3 sugar
  • that forms a phosphodiester bond between them and this is repeated many times to form a sugar-phosphate backbone
  • hydrogen bonds form between the nitrogenous bases of the antiparallel strands keeping them together
  • the hydrogen bonding between the bases also twists the strands into its double helix shape
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8
Q

What is double helix?

A

presence of 2 strands interwined

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9
Q

What is meant by antiparallel strands?

A

they run in opposite directions

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10
Q

Which bases are purines and how many rings do they have?

A
  • Adenine and Guanine

- 2 rings

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11
Q

which bases are pyrimidines and how many rings do they have?

A
  • Thymine, Cytosine and Uracil- (UCT)

- 1 ring

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12
Q

How many H bonds does A form with T and C form with G?

A
  • A with T: 2 bonds

- C with G: 3 bonds

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13
Q

State the 3 alternative models for DNA replication

A
  • semi-conservative
  • conservative
  • dispersive
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14
Q

Explain the semi-conservative model

A

two strands of the parental molecule separate, and each functions as a template for synthesis of a new, complementary strand.

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15
Q

explain the conservative model

A

two parental strands somehow come back together after acting as templates for new strands.

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16
Q

explain the dispersive model

A

a mixture of old and new DNA

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17
Q

What are origins of replication?

A

short stretches of DNA that have a specific sequence of nucleotides. and is where the replication process begins

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18
Q

what is a replication fork?

A

Y-shaped region where the parental strands of DNA are being unwound.

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19
Q

What does helicase do?

A

enzymes that untwist the double helix at the replication forks, separating the two parental strands

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20
Q

what does single-strand binding (SSB) protein do?

A

Binds and stabalizes single-stranded DNA until it is used as a template

21
Q

what does Topoisomerase do?

A

it is an enzyme that relieves overwinding strain ahead of replication forks by breaking swiveling and rejoining DNA strands

22
Q

what does primase do?

A

synthesizes RNA primers using DNA template strand

23
Q

what does DNA pol III do?

A

Synthesizes a new DNA strand by adding nucleotides on the 3’ end

24
Q

what does DNA pol I do?

A

Removes RNA nucleotides and adds DNA nucleotides

25
Q

what does DNA ligase do?

A

Joins 3’ end of DNA to rest of the leading strand and joins the Okazaki fragments of lagging strand

26
Q

What is a primer?

A

it is a short RNA strand and without it DNA polymerase wont know where to start

27
Q

How does the replication process start

A
  • proteins recognize the specific sequences of nucleotides at the origins of replication
  • they attach to the DNA and separate the strands opening up a replication bubble
28
Q

Describe the process of DNA replication (9)

A

1- Helicase separates the DNA strands by breaking the hydrogen bonds
2- topoisomerase is added to reduce strain and prevents supercoils ahead of the replication fork
3- SSB proteins binds to single DNA strands to stabilize the strands and prevent them from snapping back together
4- Primase comes in and makes RNA primer on the 3’ end of the template strands
5- DNA pol. III elongates the strand in 5’ to 3’ direction
6- it does that by moving from the 3’ to 5’ on the template strand adding nucleotides to elongate the new DNA strand
7- on the leading strand the DNA polymerase III elongates the strand continuously whereas on the lagging strands it elongates discontinuously forming okazaki fragments
8- DNA pol. I will replace primer with DNA
9- DNA ligase will join the DNA at the 3’ end to the rest of the leading strand and will seal the gaps between Okazaki fragments

29
Q

What is the leading strand?

A

it moves in the direction of the replication fork

30
Q

what is the lagging strand?

A

it moved opposite to the replication fork

31
Q

why do okazaki fragments form?

A

The template of the lagging strand goes from 5’ to 3’ and DNA polymerases can add nucleotides only to
the 3′ end
-as it replicates in the opposite way of the replication fork it forms segments due to the gaps in between

32
Q

How does proofreading take place during DNA replication?

A

If DNA polymerase makes a mistake it can stop remove the wrong nucleotide and replace it with the right one

33
Q

What is mismatch repair?

A

enzymes remove and replace incorrectly paired nucleotides

34
Q

Explain the nucleotide excision repair of DNA damage

A

1-enzymes detect and repair damaged DNA which distorts the DNA molecule.
2- nuclease enzyme cuts the damaged DNA strand at two points, and the damaged section is removed.
3- DNA polymerase adds the missing nucleotides
4- DNA ligase seals the free ends

35
Q

What is nuclease?

A

DNA cutting enzyme

36
Q

What are telomeres?

A

they are short repeated sequences

37
Q

Provide 2 functions of telomeres

A

1- prevent the staggered ends of the daughter molecule from activating the cell’s systems for monitoring DNA damage as that can lead to cell cycle arrest or death.
2- they postpone the erosion of genes near the ends of DNA molecules

38
Q

what are germ cells?

A

egg and sperm cells

39
Q

What prevents telomeres of germ cells from getting shorter?

A

telomerase

40
Q

What does telomerase do?

A

catalyzes the lengthening of telomeres in eukaryotic germ cell

41
Q

why do prokaryotes not need telomeres?

A

Most prokaryotes have a circular chromosome, with no ends, so the shortening of DNA does not occur

42
Q

How does normal shortening of telomeres prevent cancer?

A

by limiting the number of divisions that somatic cells can undergo

43
Q

What is chromatin?

A

complex of DNA and protein found in eukaryotic cells

44
Q

What proteins are responsible for the first level of DNA packing in chromatin and how do the DNA and this protein bind?

A
  • Histones

- DNA backbone has a -ve charge and histones have a +ve charge allowing them to bind tightly together

45
Q

What is a nucleosome?

A

consisting of a length of DNA coiled around a core of histones.

46
Q

How is chromatin organised into fibres to form a metaphase chromosome? mention the final width of the chromatid

A
  • DNA winds around histones to form nucleosome
  • Interactions between nucleosomes cause the thin fiber to coil or fold into this thicker fiber
  • fiber forms looped domains that attach to proteins
  • looped domains coil further forming the metaphase chromosome
  • width of a chromatid is 700 nm
47
Q

What is heterochromatin?

A

tightly packed form of DNA

48
Q

what is euchromatin?

A

loosely packed form of DNA

49
Q

why is it difficult for a cell to express genetic information coded in heterochromatin?

A

DNA is largely inaccessible to the machinery in the cell responsible for transcribing the genetic information coded in the DNA

Biology (15 decks)

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