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Biology-topic 4 DNA, genes, and protein synthesis > DNA > Flashcards

DNA Flashcards

1
Q

What is chromatin?

A

DNA and histones at any stage of the cell cycle

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2
Q

What is a chromosome?

A

compact x-shaped form of chromatin formed and visible during mitosis

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3
Q

What is a chromatid?

A

single arm of an x-shaped chromosome

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4
Q

What is the monomer of DNA?

A

nucleotides

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5
Q

Describe the structure of a nucleotide and draw it

A

a phosphate group, a pentose sugar (deoxyribose), and a nitrogenous base

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6
Q

What are the four nitrogenous bases?

A

guanine, cytosine, adenine, thymine

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7
Q

Which bases are purine bases?

A

adenine and guanine

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8
Q

Which bases are pyrimidine

A

cytosine and thymine

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9
Q

Which bases are complimentary to each other?

A

adenine and thymine, guanine and cytosine

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10
Q

What is different about the bases in RNA?

A

RNA doesn’t have thymine, it has uracil

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11
Q

What type of molecule is DNA?

A

a polymer

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12
Q

How are the mononucleotides joined together/made?

A

by a condensation reaction between the phosphate group of one nucleotide and the deoxyribose sugar of another. water is a by-product

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13
Q

What type of bond joins mononucleotides together?

A

a phosphodiester bond

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14
Q

How are two polynucleotide strands joined together?

A

by hydrogen bonds between the bases

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15
Q

How many hydrogen bonds are between each complementary base pair?

A

3 between guanine and cytosine, 2 between adenine and thymine

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16
Q

How do the two strands of polynucleotides fit together?

A

they run anti-parallel to each other- one is upside down

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17
Q

Why is it a good thing that the hydrogen bonds between the bases are weak?

A

the double helix needs to be able to be undone to allow for replication

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18
Q

Why might G-C base pairs need more energy to break their hydrogen bonds then A-T?

A

they have 3 hydrogen bonds, not 2

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19
Q

Why is DNA a stable molecule?

A

it has a double helix structure and has many weak hydrogen bonds that provide collective stability

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20
Q

Why can DNA self-replicate?

A

the 2 strands can separate easily due to the weak hydrogen bonding

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21
Q

Why are the base pairs within the sugar-phosphate backbone?

A

to prevent corruption from outside chemicals or physical forces

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22
Q

What is RNA’s job?

A

to copy and transfer genetic information from the DNA in the nucleus to the ribosomes

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23
Q

Describe the structure of RNA, and draw it

A

it is made from a phosphate group, a pentose sugar (ribose), and a nitrogenous base

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24
Q

What does Chargaff’s rule state?

A

that the DNA of any species contains equal amounts of adenine and thymine, and equal amounts of cytosine and guanine

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25
How was the structure of DNA discovered?
by using x-ray crystallography
26
When comparing RNA and DNA, what 3 things should you mention?
the type of sugar, the bases involved, and the number of strands
27
Compare the shape of DNA vs RNA
DNA is double stranded and twisted into a double helix, fixed in place by hydrogen bonds, whereas RNA is single-stranded
28
Compare the sugar in DNA vs RNA
DNA has a deoxyribose sugar, whereas RNA has a ribose sugar. both are pentose sugars
29
Compare the bases in DNA vs RNA
DNA has G/C/A/T, whereas RNA has G/C/A/U
30
Compare the relative size of DNA vs RNA
DNA is a large/long molecule, whereas RNA is relatively short
31
What are the different types of RNA?
messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA)
32
What is the job of mRNA?
it carries the genetic information/code from the DNA from the nucleus to the cytoplasm
33
What are the two stages of protein synthesis/DNA replication?
transcription- where the DNA code is copied into mRNA translation- where the mRNA joins with a ribosome and the code is used to synthesise a protein
34
What are the different names for 3 bases in DNA vs 3 bases in RNA?
DNA- 3 bases is a triplet RNA- 3 bases is a codon
35
What is mRNA?
a copy of a gene from DNA
36
Why can't DNA leave the nucleus?
it is too large and would be at risk of being damaged by enzymes which would destroy the genetic code
37
Why can mRNA leave the nucleus?
although it doesn't have a fixed length, it is much shorter than DNA
38
Why does the presence of enzymes not matter for mRNA?
it is only needed temporarily to help create a protein, so by the time enzymes could break it down, it would have already done it's job
39
Every 3 bases code for...
a specific amino acid
40
What is the start codon for all strands of mRNA?
A U G
41
How do you distinguish which is the mRNA strand and what are the two called?
the sense strand contains thymine, the mRNA strand has uracil
42
What is the name of mRNA's structure?
linear
43
Where is tRNA found?
only in the cytoplasm
44
Describe the structure of tRNA
single polynucleotide strand with hydrogen bonding between parts, giving it a fixed clover leaf shaped structure
45
What is the name of the start of the tRNA?
amino acid attachment site
46
What is at the bottom curve of the tRNA molecules?
the anticodon, which is made up of 3 bases that are complementary to the codon on mRNA
47
What are the 3 types theories of DNA replication?
conservative, semi-conservative, dispersive
48
What is the function of tRNA?
to attach to one of the 20 amino acids and transfer it to a ribosome to create the polypeptide chain
49
What does ribosomal RNA do?
combines with protein to make ribosomes
50
What is conservative replication theory?
one molecule of original DNA, new molecule of newly synthesised DNA
51
What is dispersive replication theory?
the double helices are part original and part newly synthesised DNA
52
What is the semi-conservative replication?
when there is one original strand and one newly synthesised strand in each DNA molecule
53
Why does DNA copy itself before replication takes place?
so that each new cell has the full amount of DNA
54
What did Meselson and Stahl's experiment prove?
that DNA replication must be semi-conservative
55
Why are DNA bases called nitrogenous bases?
they contain nitrogen
56
In order to make new DNA nucleotides, what do (bacteria) do?
take in nitrogen isotopes in the medium they're growing in
57
Explain the Meselson and Stahl experiment
-bacterial (E.coli) cells are grown in 15N medium for several generations, then are transferred to 14N medium, then extracted and undergo density gradient centrifugation - the first generation of the bacterial cells that have been transferred to 14N medium and left to replicate, then are extracted and undergo density gradient centrifugation -the second generation of the bacterial cells that have been transferred to 14N medium undergo the same thing, as well as the third generation
58
How does the density gradient centrifugation work?
by using solutions of decreasing density of caesium chloride, with the most dense caesium chloride at the bottom. as the tubes are centrifuged, the DNA moves to the position where their density corresponds to that of the caesium chloride solution, and can then be viewed under UV light
59
What is the general pattern of the position of the bands as the generations increase?
the bands tend to move up the tube as generations progress
60
Give 3 ways in which DNA's structure enables it to carry out it's functions
double helix- makes it stable 2 strands can separate easily due to weak hydrogen bonds- for self-replication large molecule- carries lots of information
61
Give 2 differences between the structures of mRNA and tRNA
mRNA- linear shaped tRNA- clover leaf shaped mRNA- variable length of nucleotides tRNA- fixed length of nucleotides
62
What is meant by specific base pairing?
bases have to be complementary to each other, like A-T
63
Why is specific base pairing important?
as both strands act as a template
64
Explain the process of DNA replication
-replication starts at a specific sequence on the DNA molecule called the replication origin -the enzyme DNA helicase unwinds and unzips the DNA, breaking the hydrogen bonds that join the base pairs, leaving 2 separate strands -free nucleotides from the nucleoplasm are attracted to their exposed complimentary bases on the original template strands of DNA -DNA polymerase joins the new nucleotides to each other adjacently -a winding enzyme then winds up the new strands to form double helices -the new molecule is exactly identical to the original one
65
Why do we need the cell cycle?
for growth and repair
66
What are the stages of the cell cycle?
interphase (g1/s (synthesis)/g2) mitosis cytokinesis
67
What happens during interphase?
the cell grows in size, organelles are replicated, and the DNA is replicated
68
What are the 4 stages of mitosis?
prophase metaphase anaphase telophase
69
What happens in prophase?
chromosomes condense and become more visible, spindle fibres start to form, the nuclear membrane breaks down, and the centrioles move to opposite sides of the cell
70
What happens during metaphase?
the chromosomes attach to the spindle fibres at the centromere, and line up along the equator of the cell
71
What happens during anaphase?
spindle fibres contract which divides the centromere, which separates the sister chromatids and pulls them towards opposite poles
72
What happens during telophase?
the nuclear membrane reforms around each set of daughter chromosomes
73
What is g1?
growth and normal function occurs
74
What is s phase?
DNA replication occurs and there is a build-up of ATP stores
75
What is g2?
growth and checkpoint phase which checks and repairs damage to the DNA
76
What happens during cytokinesis?
the cytoplasm divides
77
What is mitotic index?
number of cells in mitosis/ total number of cells
78
What is cancer?
uncontrolled cell division leading to group of abnormal cells called a tumour
79
What are the two main ways of treating cancer?
preventing DNA from replicating (disrupting s-phase of interphase) inhibiting the metaphase stage of mitosis by interfering with spindle fibre formation
80
What are the problems with chemotherapy and why?
it also disrupts the cell cycle of normal cells, and is more effective on fast growing cells. cancer is fast growing but so are your hair and nails

Biology-topic 4 DNA, genes, and protein synthesis (6 decks)

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