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Biology > Nucleic Acids > Flashcards

Nucleic Acids Flashcards

1
Q

Why are nucleic acids important?

A

They are essential to heredity in living organisms

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2
Q

What does every human cell contain?

A

46 Chromosomes
2 Metres of DNA
Around 3 billion nucleotides

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3
Q

What bonds form between nucleotides?

A

Phosphodiester bond

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4
Q

What bonds form between bases?

A

Hydrogen bonds

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5
Q

What makes up a nucleotide?

A

A nitrogenous base, pentose sugar and a phosphate group

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6
Q

How does the phosphodiester bond form?

A

Through a condensation reaction between the phosphate group at position carbon 5 on one nucleotide and the the hydroxyl group at carbon 3 on the other nucleotide

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7
Q

What are the purines?

A

Adenine and Guanine

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8
Q

What is a purine?

A

Larger bases that contain a double carbon ring structure

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9
Q

What are the pyramidines?

A

Thymine and Cytosine

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10
Q

What is a pyramidine?

A

Smaller bases that contain single carbon ring structures.

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11
Q

What are the differences between DNA and RNA?

A

DNA has 2 strands whereas RNA has 1
DNA contains deoxyribose whereas RNA contains ribose
DNA contains A,T,C,G whereas RNA contains A,U,C,G

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12
Q

Why is the pentose sugar ‘deoxyribose’ named that?

A

Because it is has one less oxygen atoms than ribose

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13
Q

What is the structure of DNA?

A

It is a double-helix

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14
Q

What is complimentary base pairing?

A

A forms two hydrogen bonds with T and G forms three hydrogen bonds with C. This means that purines always bond with a pyramidine due to the difference in size.

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15
Q

Why is RNA less stable than DNA?

A

Because it has one more Oyxgen atom than DNA.

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16
Q

How can you purify DNA by precipitation (part 1)

A
  1. Grind sample in mortar and pestle to break down cell walls
  2. Mix sample with detergent to break down cell surface membrane, releasing the cell contents into solution
  3. Add salt to break the hydrogen bonds between DNA and the water molecules
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17
Q

How can you purify DNA by precipitation (part 2)

A
  1. Add protease to break down proteins associated with DNA in the nuclei
  2. Add layer of alcohol to cause DNA to precipitate out of solution
  3. Use a glass rod to spool the white strands of DNA
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18
Q

What phases of mitosis does DNA replication occur?

A

In interphase.

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19
Q

What does semi-conservative replication mean?

A

That the two daughter strands are made up of one old template strand and one newly replicated strand.

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20
Q

What does degenerate code mean?

A

That one amino acid can be coded for by more than one codon

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21
Q

Why is DNA non-overlapping?

A

Because one nucleotide is only part of one triplet.

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22
Q

Why is DNA replication continuous and discontinuous?

A

Because DNA polymerase works in a 5’ to 3’ direction, it is able to synthesis the leading strand continuously but has to synthesise the lagging strand in a 3’ to 5’ direction in Okozaki fragments.

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23
Q

Where does DNA replication begin?

A

At the origin, which eukaryotic cells have multiple sites of origin.

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24
Q

How did the Meselson and Stahl experiment prove that DNA replication is semi-conservative? (part 1)

A

Because after the first replication the band of DNA was in the middle of the centrifuge tube, which showed that the new DNA was half heavy nitrogen and half light nitrogen. However, this could shows either semi-conservative or dispersive replication.

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25
Q

How did the Meselson and Stahl experiment prove that DNA replication is semi-conservative? (part 2)

A

After a second replication, there were two bands, one of light nitrogen, which showed two daughter DNA of completely new DNA and one in the middle, which was half light and half heavy nitrogen, which showed that there were two DNA with one old and one new strand.

26
Q

What are the steps of DNA replication?

A
  1. DNA helicase breaks the hydrogen bonds between the bases, creating a replication fork. The two strands are now separated.
  2. Free nucleotides that have been activated are attracted to their complementary bases.
  3. Once the free nucleotides have been lined up, they (bottom three nucleotides) are joined together by DNA polymerase, which forms phosphodiester bonds.
  4. Finally, all the nucleotides are joined together to form a polynucleotide. Both strands consist of one old strand and one newly replicated strand.
27
Q

What ability does DNA polymerase have?

A

It has proof-reading ability. DNA polymerase makes 1 mistake for every billion base pairs copied. When an incorrect base is pair is recognised, DNA polymerase moves back one base pair.

28
Q

Does the correct base pair with the complementary base straight away?

A

No, it does not. DNA polymerase waits until the right base has been put in until it can move a long.

29
Q

What is a start codon?

A

A codon that indicates where DNA polymerase should read the genetic code. Every reading frame is ATG.

30
Q

What is the reading frame on every genetic code?

A

ATG

31
Q

What is a stop codon?

A

A codon that indicated where DNA polymerase should stop reading the genetic code.

32
Q

What are examples of stop codons?

A

TAG, TAA, TGA

33
Q

What does DNA polymerase need in order to start synthesis?

A

It requires a free 3’ hydroxyl group on the deoxyribose

34
Q

Why are Okozaki Fragments created?

A

-DNA polymerase can only copy DNA in the 5’ to 3’ direction
-This means that it can continuously replicate the leading strand as it moves from the initial point of separation along the strand.
-To copy the lagging strand, the polymerase has to replicate backwards along the strand to the initial point of separation. -
Replication then stops, moves up the strand and moves backwards again to the segment that has already been copied. -
A series of disconnected DNA segment copies called Okazaki fragments are produced from the lagging strand.

35
Q

What is transcription?

A

Making a copy of something

36
Q

What is translation?

A

Process of converting something from one form into another

37
Q

Why must transcription occur?

A

Because DNA is too long to leave the nucleus so a short section of DNA, equivalent to one gene is transcribed onto a mRNA molecule so it can leave the nucleus.

38
Q

What are the three stages of transcription?

A

Initiation
Elongation
Termination

39
Q

What happens in initiation? TRANSCRIPTION

A
  • RNA polymerase binds to the promoter region near the beginning of a gene held on the DNA
  • The DNA is unzipped to make two strands of single stranded DNA
  • The SENSE strand holds the triplet code for the sequence of amino acids
  • The ANTISENSE strand does not code for the sequence of amino acids but is complementary in base sequence to the SENSE DNA strand.
  • The ANTISENSE DNA strand acts as a template strand for RNA polymerase so that the mRNA sequence is the same as the SENSE DNA strand.
40
Q

What happens in elongation? TRANSCRIPTION

A
  • RNA polymerase travels a long the DNA template strand (antisense)
  • RNA polymerase matches complementary nucleotides to the bases on the DNA to make a complementary base sequence mRNA molecule.
41
Q

What happens in termination? TRANSCRIPTION

A
  • At the end of a gene, RNA polymerase will encounter a stop triplet that terminates the production of mRNA (leaves it the length of one gene)
  • RNA polymerase will detach from the DNA and release the newly made mRNA
  • mRNA molecule is free to leave nucleus through nuclear pore
  • DNA rewinds to form double helix DNA
  • RNA polymerase makes more mRNA molecules.
42
Q

What makes up a ribosome?

A
  • They are made up of rRNA (ribosomal) and proteins

- Ribosomes have a large ribosomal subunit and a small ribosomal subunit.

43
Q

What does the small ribosomal subunit do?

A

Reads the mRNA

44
Q

What does the large ribosomal subunit do?

A

Has two binding sites for tRNA molecules and is a catalytic site for joining amino acids together.

45
Q

What are the stages of translation?

A

Initiation
Elongation
Termination

46
Q

What happens in initiation? TRANSLATION

A
  • Small ribosomal subunit binds to the mRNA at the start codon
  • tRNA with anticodon UAC binds to complementary codon AUG by complementary base pairing, bringing the amino acid methionine
  • Large ribosome subunit attaches to the small subunit.
47
Q

What happens in elongation? TRANSLATION

A
  • Another tRNA molecule binds to the mRNA by complementary base pairing, bringing a specific amino acid
  • Catalytic site on ribosome called peptidyl transferase creates a peptide bond between methionine and the amino acid brought by tRNA through a condensation reaction
  • Ribosome moves a long the mRNA by one codon so the second tRNA bind site is clear
  • Another tRNA molecule joins and the process goes on and on until the polypeptide is complete
48
Q

What happens in termination? TRANSLATION

A
  • Ribosome encounters a stop codon on the mRNA
  • Stop codon causes the ribosomal subunits to detach from each other and from mRNA
  • Polypeptide is processed and modified through the Golgi apparatus to from a protein.
49
Q

What is ATP referred to as?

A

The universal energy currency

50
Q

What is ATP classified as?

A

A nucleoside triphosphate

51
Q

What makes up ATP?

A

Adenine, 3 phosphates, ribose

52
Q

What is ATP used for?

A

Energy transfer in cells of all living things

53
Q

What is the equation for ATP?

A

ATP + H20 <=> ADP + Pi

54
Q

Why is ATP used as an energy source?

A
  • Because the terminal gamma phosphate requires little energy to break the weak bond
  • So, when the bond breaking is coupled with a bond making reaction, that occurs at the same time, a large amount of energy is released.
  • Cell can use this energy
55
Q

How much energy does ATP release?

A

30.6kJmol-1

56
Q

What is the concentration ratio of ATP to ADP in cells?

A

ATP concentrations are 5 fold-fold higher than concentration of ADP

57
Q

Where does ATP production occur?

A

Mainly in the mitochondria

58
Q

What percentage of volume to mitochondria make up in a typical eukaryotic cell?

A

25%

59
Q

What are the properties of ATP that make it a good energy source for cells?

A
  • Short-term storage
  • Made and then consumed by cellular reactors so is an IMMEDIATE source
  • Soluble in water so can dissolve in the cytoplasm, often bound to M2+
  • Small so allows transport around and between cells
  • Easily regenerated as it can be made from ADP and Pi by a condensation reaction
60
Q

What is an anticodon?

A

A trinucleotide sequence, complimentary to the corresponding codon on a mRNA molecule

61
Q

When is ‘triplet’ and when is ‘codon’ used?

A
  • ‘Triplet’ is used in reference to DNA

- ‘Codon’ is used in reference to RNA

Biology (33 decks)

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