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π’»π“Šπ“ƒπ’Ήπ’Άπ“‚π‘’π“ƒπ“‰π’Άπ“π“ˆ π‘œπ’» 𝓉𝒽𝑒 𝓁𝒾𝓋𝒾𝓃𝑔 𝒸𝑒𝓁𝓁 > DNA structure > Flashcards

DNA structure Flashcards

1
Q

Describe basic DNA Structure & Function:

A

β†’DNA is the store of genetic information

β†’ it is made of a double helix (consists of major and minor grooves which are receptors for drugs)

β†’DNA bases encode genetic information

β†’DNA is present as chromatin in the nucleus It can be damaged by radiation and chemicals

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2
Q

what are the four bases and describe their composition

A

β†’ adenine, thymine, guanine and cytosine

β†’Adenine and Guanine are Purines, they have 2 benzene rings.
β†’Thymine and Cytosine are Pyrimidine, they have 1 benzene ring.

β†’Adenine and Thymine have 2 H bonds between them.
β†’Guanine and Cytosine have 3 H bonds between them.

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3
Q

how many forms does DNA have?

A

3 forms

A,B and Z

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4
Q

describe A DNA

A 
A-FORM DNA 
β†’The A form is wider than B 
β†’it is clockwise and has right-handed turns. 
β†’A-form is found in RNA and tRNA
β†’ it is 20-25% shorter than B DNA.
β†’ the grooves are identical in width 
β†’ 11 base pairs per turn 
β†’ more tightly coiled than B
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5
Q

describe B DNA

A 
B-FORM DNA: 
β†’ most common form of DNA found in cells 
 β†’It is clockwise 
β†’ right handed helix 
β†’ minor groove is 120 degrees
β†’ major groove is 240 degrees 
β†’ 10 bases per turn
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6
Q

describe Z DNA

A

β†’ Present in small amounts in the cell.
β†’ Z DNA may be found in cells under certain conditions (eg: high salt conditions).
β†’ 12 bps per turn.
β†’ left handed helix.
β†’ alternating purine and pyrimidine bases.

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7
Q

give a summary of the DNA helix

A

β†’two antiparallel polynucleotide strands form a right hand helix
β†’ the bases are on the inside and the sugars and phosphates are on the outside
β†’ the diameter is 2nM
β†’ one strand is complementary in sequence to another
β†’ the polynucleotide chains are held together by H bonds between pairs of bases

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8
Q

Describe bacterial DNA

A

β†’ DNA is circular
β†’ has 3 million base pairs
β†’ supercoiled
β†’ Bacterial cells also have plasmids that only carry certain genes. eg: those for antibiotic resistance.
β†’ E.coli chromosome is circular and organized into 50 independently supercoiled domains.

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9
Q

what is bacterial DNA supercoiled by?

A

DNA gyrase

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10
Q

Describe eukaryotic DNA.

A

β†’ humans have 3 billion base pairs of DNA
β†’ DNA is complexed with histones and made into a fiber called chromatin
β†’ the double helix is wound around 8 histone subunits

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11
Q

What are some reasons as to why mutations may occur in DNA?

A

SPONTANEOUS
β†’ loss of bases
β†’ hydrolysis of C to U

CHEMICALS
β†’ change of base structure
β†’ insert between bases (doxorubicin used as anticancer drugs)

RADIATION
β†’ UV light produces thymine dimers
β†’ ionizing radiation break DNA chromosomes to cause leukemia

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12
Q

what is the importance of DNA repair?

A

β†’ maintains the genome stability.

β†’ 50-100 enzymes/proteins to check that DNA is properly repaired.

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13
Q

what is an example of a disease due to failed repair mechanisms?

A

β†’Xeroderma pigmentosum
β†’ defect in excision repair that deals with UV damage to DNA
β†’prone to skin cancer

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14
Q

describe the Holliday junction and when it forms

A

β†’A Holliday Junction is a cross-shaped structure that forms during the process of genetic recombination.

β†’ two double-stranded DNA molecules become separated into four strands in order to exchange segments of genetic information.

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15
Q

what is tetraplex DNA and where is it found?

A

DNA formed by the DNA folding back on itself found at the telomeres.

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16
Q

describe how the nucleotides are arranged

A

β†’linked by 3’ 5’ phosphodiester bonds
β†’ DNA runs from 5’ to 3’
β†’ the two strands of DNA that are bonded together by H bonds run antiparallel to each other

17
Q

What are 4 main points of DNA structure?

A

β†’ Primary: The sequence of DNA bases (ATCG) and their combinations.

β†’ Secondary: conformational form, A,B,C, or Z which is detected using X-Ray Crystallography.

β†’ Tertiary​: DNA supercoiling, detected using electron microscopes.

β†’ Quaternary​: interlocked chromosomes.

18
Q

When is A - form DNA found in the cell?

A

A - form occurs under dehydrating conditions​.

19
Q

What are the potential consequences of DNA repair defects?

A

β†’ DNA repair defects = cancer likely.
β†’ Hereditary DNA repair defects, due to mutations, so unable to repair DNA properly.
β†’ Mutations in DNA lead to formation of tumours.

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