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Biology A Level > DNA > Flashcards

DNA Flashcards

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1
Q

What is the sugar in DNA known as?

A

Deoxyribose

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2
Q

What are the 4 nitrogenous bases?

A

Adenine, Guanine, Cytosine, and Thymine

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3
Q

which of the nitrogenous bases are the purines?

A

Adenine and Guanine

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4
Q

which of the nitrogenous bases are the pyrimidines?

A

Cytosine and Thymine

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5
Q

How are each nucleotide in the Backbone bonded to each other?

A

Phosphodiester bonds

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6
Q

What are the nitrogenous bases pairs?

A

Adenine + Thymine

Cytosine + Guanine

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7
Q

how are each base pair connected?

A

Hydrogen bonds

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8
Q

What is the function of the Sugar-phosphate backbone?

A

to provide stability, preventing DNA corruption and mutation

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9
Q

What is the function of the hydrogen bonds ?

A

provides more stability

strands can be easily separated when needed

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10
Q

How do the sugars in each Nucleotide connect to each other?

A

The 3rd Carbon in one sugar connects to the 5th, and vice versa

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11
Q

How do the Backbones run together?

A

They run antiparallel, meaning that the 3’ sugar is next to the 5’ sugar

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12
Q

How many bonds are in the Base pairs?

A

2 in A+T

3 in C+G

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13
Q

What are the Nucleotides built of?

A

Nitrogenous base, Deoxyribose and a phosphate group

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14
Q

Describe how DNA is packaged in a cell.

A

1 - DNA is wrapped around histones
2 - The Histones+DNA is wrapped into a double helix
3 - The DNA is looped around a protein core to form a 300nm fibre

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15
Q

What is a gene?

A

A piece of DNA that codes for a particular protein

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16
Q

what does a chromosome consist of?

A

lots of DNA molecules

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17
Q

what does a DNA molecule consist of?

A

Lots of genes

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18
Q

What does a gene consist of?

A

Lots of codons

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19
Q

what does a codon consist of?

A

3 bases

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20
Q

What are coding sequences?

A

Regions of DNA which code for a particular protein or functional RNA, eg tRNA or rRNA

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21
Q

What are non-coding sequences?

A

DNA regions that do not encode for anything, they can be regulatory, protective, or junk DNA

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22
Q

What is a gene?

A

A specific DNA base sequence that codes for a particular protein or functional RNA

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23
Q

What does a codon code for?

A

a particular Amino Acid

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24
Q

How many codons are in most organisms ?

A

64 codons, with 1 being a start (ATG) and 3 being stop codons.

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25
Q

What does a stop codon do?

A

Signal the end of a polypeptide chain

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26
Q

What are some differences between DNA and RNA

A 
DNA
Double stranded
Contains deoxyribose 
Contains thymine
Stable
RNA
Single stranded
Contains ribose 
Contains uracil
Only lasts 20-30 minutes - unstable
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27
Q

What is mRNA?

A

Messenger RNA

28
Q

What does messenger RNA do?

A

It transports information (RNA) from the nucleus to the ribosomes, in order to create proteins (polypeptides)

29
Q

What type of replication does DNA undergo?

A

Semi-conservative replication

30
Q

What enzymes pulls apart the DNA helix?

A

DNA helicase

31
Q

What enzymes bonds the deoxyribose-phosphate backbone?

A

DNA polymerase

32
Q

In a newly replicated DNA helix, what are the strands in relation to their old helix?

A

One strand of the helix is newly replicated,and one is from the old helix, which acts as a template.

33
Q

What is produced when DNA wraps around a histone?

A

nucleosome

34
Q

What is a chain of nucleosomes called?

A

chromatin

35
Q

What is the difference between prokaryotes and eukaryotes in terms of histones ?

A

Prokaryotes
No histones, meaning no chromatin. Looped DNA and a supercoiled nucleus
Eukaryotes
DNA+Histones form nucleosomes, forming chromatin

36
Q

What is the difference between prokaryotes and eukaryotes in terms of chromosomes?

A

Both contain chromosomes, whereas P have short + circular DNA making up a chromosome, whereas E have one long DNA molecule making up a chromosome

37
Q

What is the difference between prokaryotes and eukaryotes in terms of Plasmids

A

Prokaryotes may have circular plasmids, whereas Eukaryotes do not

38
Q

How many chromosomes are present in the body?

A

23 Homologous pairs

39
Q

What is the name for different versions of the same gene in Homologous chromosomes?

A

Alleles

40
Q

What causes Alleles?

A

minor variations in the sequence

41
Q

Where is the start Codon found?

A

at the 5’ end of the gene

42
Q

what are exons?

A

coding regions of the gene, containing codons

43
Q

what are introns?

A

non coding regions found in between exon, which don’t contribute to the final protein

44
Q

where is the stop codon found?

A

at the very 3’ end of the gene

45
Q

What are the stages of mitosis?

A

(Interphase), prophase, metaphase, anaphase, telophase, and cytokinesis

46
Q

What happens during prophase?

A

Chromosomes become visible, forming chromatids as they duplicate. The nuclear membrane breaks down in this stage

47
Q

What happens during metaphase?

A

Spindle figures attach the chromatids and the centrioles together, whilst the chromatids line up along the equator of the cell

48
Q

What happens during anaphase?

A

Identical chromatids are pulled to either poles of the cells by the spindle fibres

49
Q

What happens during telophase?

A

Chromatids (chromosomes) are at the poles, and the nuclear membrane begins to form. Cleavage is visible at this point.

50
Q

What happens during cytokinesis?

A

The cytoskeleton breaks down, splitting the cells forming two identical daughter cells

51
Q

What is cancer?

A

Uncontrolled cell division which causes a malignant tumour

52
Q

What causes cancer?

A

Damage to the DNA/genes which repair DNA and cause faulty cells to apoptosise, through carcinogens or inheritance.

53
Q

What is metastasis?

A

When parts of the tumour break off and spreads through the bloodstream to another part of the body.

54
Q

What are the stages of cell fractionation .

A

Homogenisation
Filtration
Ultracentrifugation

55
Q

Are viruses alive?

A

No, as they cannot replicate/reproduce on their own, and don’t satisfy any of the qualities that make something considered living.

56
Q

How do Viruses replicate?

A

They have particular proteins on their surface which attach to certain cells, they then inject themself into the cell, and using the cell’s organelles (ribosomes, Endoplasmic reticulum, etc) they create more viral DNA/RNA, producing more viruses until the cell explodes, releasing more.

57
Q

What happens in the nucleus during transcription?

A

DNA Helicase unwinds the DNA, revealing a template strand, which free floating nucleotides bond to, whilst RNA polymerase moves along, bonding the bases, forming a pre-mRNA molecule. DNA rejoins behind the pre-mRNA molecule. This continues until a stop codon is reached, when the pre-mRNA detaches.

58
Q

What happens before leaving the nucleus in transcription?

A

The pre-mRNA is spliced, removing introns, which would interfere with the production of a polypeptide. This forms mRNA, which only contains exons.

59
Q

What happens after splicing in transcription?

A

The mRNA leaves the nucleus through a nuclear pore, before moving to a ribosome.

60
Q

What is the first stage of translation?

A

A ribosome attaches to the start codon of a mRNA molecule, and a tRNA molecule joins to the codon on the mRNA molecule with its anticodon. This tRNA carries a specific amino acid, and whilst another tRNA bonds to the next codon, it joins the two amino acids by a peptide bond, and floats off, allowing another tRNA molecule to join next in line. This repeats.

61
Q

What is the final stage of translation?

A

This cycle repeats, creating a long polypeptide chain, until a stop codon is reached, and the ribosome and polypeptide detach.

62
Q

What evidence is there for Semi-conservative replication?

A

Meselson and stahl’s experiment.

63
Q

Describe meselson and stahl’s experiment

A

1) M&S grew Bacteria (e. Coli) in a medium containing 15N (heavy nitrogen).
2) they centrifuged this and found where the DNA settled
3) they removed the bacteria and put them in a medium containing 14N (light) and would allow them to replicate once for one generation and centrifuge the sample.
4) They would repeat this for 3 generations.

64
Q

Describe the findings of Meselson and Stahl’s experiment

A

1) G0 had 100% of DNA being 15N-15N and settled at the bottom after centrifugation
2) G1 had 100% of DNA being 15N-14N and settled slightly higher that G0
3) G2 had 50% 14N-14N and 50% 15N-14N, giving two bands. The lower band contained the heavy nitrogen as it is denser and settled lower.
4) G3 had 75% of DNA as 14N-14N and 25% of DNA as 15N-14N

65
Q

What are two similarities between prokaryotic, mitochondrial and chloroplast DNA

A

Their DNA is circular

Their DNA is not associated with histones

66
Q

Give the differences between mRNA and tRNA

A 
tRNA
-is a folded strand
-has an amino acid binding site
-has an anticodon
mRNA 
-is a straight stand
-has a codon

Biology A Level (23 decks)

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