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Year 12 - Biology > C4 - Nucleic Acids > Flashcards

C4 - Nucleic Acids Flashcards

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1
Q

What is a nucleotide?

A

A monomer made from a nitrogen containing base, phosphate group and pentose sugar.
Nucleotides can be joined together to form polynucleotides.

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2
Q

What type of pentose sugar is found in DNA, Deoxyribonucleic acid?

A

Deoxyribose

C5 H10 O4

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3
Q

What type of pentose sugar is found in RNA, Ribonucleic acid?

A

Ribose

C5 H10 O5

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4
Q

What are the 3 distinct parts of a nucleotide?

A
  • phosphate group (represented by a circle)
  • pentose sugar (represented by a pentagon)
  • nitrogen-containing base (represented by a hexagon)
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5
Q

What are the 2 main groups of the nitrogen containing base?

A

Purines - have double ring structures (guanine and adenine)

Pyrimidines - have single ringed structures (cytosine, thymine and uracil)

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6
Q

What are the 2 purine bases?

A

Adenine

Guanine

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7
Q

What are the 3 pyrimidine bases?

A

Cytosine

Thymine (found in DNA )

Uracil (found in RNA)

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8
Q

Who discovered the order of the component of a nucleic acid?

A

Phoebus Levene - he discovered the phosphate-sugar base

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9
Q

What type of reaction forms the bonds which hold the phosphate to the sugar and the base to the sugar?

A

Condensation reaction

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10
Q

What type of bond is present between the phosphate & sugar and the base & sugar?

A

A phosphoester bond

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11
Q

What do the purines bind to?

A

Adenine binds to Thymine or Uracil

Guanine binds to Cytosine

Each pair is found in equal numbers

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12
Q

What do the pyrimidines bind to?

A

Thymine or Uracil bind to adenine

Cytosine binds to guanine

Each pair is found in equal numbers

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13
Q

What is ATP?

A

Adenosine triphosphate is used for intracellular transfer of substances and provides energy to the cell.

It can be hydrolysed to release energy from ADP and further hydrolysis forms AMP which can be reverted back through phosphorylation.

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14
Q

Who identified the structure of DNA?

A

Watson and Crick found the double stranded structure.

Franklin identified the double helix structure.

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15
Q

What is DNA?

A

Deoxyribonucleic acid is a double-stranded polymer of nucleotides made from the pentose sugar ‘deoxyribose’ and the A, G, C and T bases.
It consists of 2 anti-parallel chains of nucleotides held in place by hydrogen bonds.

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16
Q

What 2 rules were identified by Chargaff?

A

1) In natural DNA, G units is equal to C units and A is equal to T units.
2) The composition of DNA varies from one species to another.

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17
Q

What are the 4 steps to the formation of DNA?

A

The nucleotides/bases line up.

The bases attach to the sugar to form the sugar-phosphate back bone.

Complementary bases are paired up.

The strands twist to form a helix / helical structure

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18
Q

What are the 4 properties of DNA?

A
  • The two polynucleotide strands are wound in a ‘double helix’
  • Complementary base pairing (A & T, C & G)
  • Anti-parallel strands
  • It’s a stable molecule held together by covalent bonds called phosphodiester bonds which give the s-p-backbone strength. In eukaryotes, its made more stable by coiling around histone proteins to form chromosomes.
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19
Q

How is DNA extracted?

A

You swirl water in your mouth then spit it into a test tube and add detergent solution, salt solution and protease solution.
The test tube is then placed in a warm water bath for 10 mins to provide kinetic energy to speed up the reaction.
Ethanol is then added which is non polar (and the DNA is polar) so the DNA separates and forms a globular, floating precipitate.

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20
Q

Why is detergent, salt and protease solution added to extract DNA?

A

Detergent - breaks down the phospholipid bilayer of the cell membranes and helps break open the cell

Salt - has an ionic structure which separates into positive and negative ions which neutralizes the sugar-phosphate back bone and opens the helix structure.

Protease - helps break down the proteins of the cell membrane and nuclear envelope so the DNA can be obtained (specifically histone proteins)

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21
Q

Why is it necessary that DNA replicates?

A

Cells making up organisms are always produced from pre-existing cells via cell division.

The nucleus and all DNA must be copied exactly to ensure that all daughter cells have the correct genetic info to produce the required proteins.

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22
Q

What are the 3 theories behind DNA replication?

Which is the one we use today?

A

Conservative: makes complete clone with new nucleotides

Semi-conservative: daughter DNA has one old strand and one new strand

Dispersive: has old and new nucleotides in the same strand

(All double helix)

We believe in the semi-conservative mechanism of DNA replication.

23
Q

How does DNA replicate?

Semi-conservative

A

1) Histones are removed from the DNA
2) The DNA molecule is unwound and separated by helicase enzymes which breaks the hydrogen bonds between the base pairs.
3) The two DNA strands are kept apart by single stranded bonding proteins and are exposed, acting as template strands.

4) DNA polymerase enzymes bind to each template strand and catalyse the formation of new strands.
The nucleotides are activated by the addition of 2 phosphate groups from ATP.

5) The activated DNA nucleotides diffuse through the nucleoplasm and align next to their complementary bases on the exposed template strands.
They are then bonded by hydrogen bonds.

6) DNA polymerase reads the parent strand in a 3’ to 5’ direction and builds the leading strand in a 5’ to 3’ direction towards the replication fork.
It also joins the nucleotides to neighbouring nucleotides by catalysing a condensation reaction to form phosphodiester bonds.

7) Synthesis differs slightly on the two strands as they’re anti parallel. The lagging strand is built 3’ to 5’ away from the replication fork discontinuously in Okazaki fragments.
DNA ligase joins the sections to form a long polynucleotide.

8) The DNA helix continues to unwind and separate and the leading strand grows continuously towards the replication fork meanwhile the lagging strand grows discontinuously away from the fork.
9) There are multiple replication forks along single molecules to speed up replication.
10) The double stranded DNA molecules are rewound and wrapped around Histones to form chromosome copies.

24
Q

What are the four key requirements for DNA replication?

A
  • four different types of DNA nucleotides ATCG
  • the original DNA molecule to act as two template strands
  • specific enzymes including DNA polymerase and DNA ligase to catalyse the reaction
  • ATP to provide energy for the process
25
Q

What are the two anti-parallel strands called during DNA replication?

A

The leading strand and the lagging strand

26
Q

What are Okazaki fragments?

A

Short nucleotide sequences

27
Q

What does DNA ligase do?

A

It joins up the short nucleotide sequences (Okazaki fragments).

28
Q

What does DNA helicase do?

A

It separates the 2 DNA strands and breaks the hydrogen bonds between the base pairs.

29
Q

What does DNA polymerase do?

A

It binds to each of the DNA template strands and catalyses the formation of new strands.

30
Q

What is the genetic code?

A

Distributed across the chromosomes are genes which code for the production of a polypeptide chain.
The length of DNA making up a gene carries the instructions to make a specific protein, known as the genetic code.

31
Q

What is the triplet code?

A

By using a combination of three bases there are 64 possible combinations (more than enough to code for the 20 different amino acids)

32
Q

What is a codon?

A

A DNA triplet

Methioine acts as the start

33
Q

What are the 4 facts of the genetic code?

A
  • They’re found in triplets
  • It’s degenerate (there is more than one codon for most amino acids)
  • It’s non-overlapping (each base is only part of one codon)
  • It’s universal (it’s the same for almost all organisms)
34
Q

What are the three types of RNA?

A

mRNA (messenger RNA)

tRNA (transfer RNA)

rRNA (ribosomal RNA)

35
Q

What is RNA?

A

A single stranded molecule made of a pentose sugar (ribose), phosphate group and nitrogen containing base (AUGC)

36
Q

What does mRNA do?

A

When a polypeptide is needed, the triplet code of its gene is converted into a molecule of mRNA.
This is called transcription.

mRNA carries genetic info from the nucleus to the site of protein synthesis (ribosomes in cytoplasm)

37
Q

What does tRNA do?

A

It is a single stranded RNA polynucleotide chain that carries a specific amino acid to the ribosome during translation.

In cytoplasm, amino acids become attached to tRNA.
Each is specific for one amino acid.
Each tRNA molecule has a sequence of 3 bases called an anticodon.
These are complementary to codons on the mRNA.
(Complementary codon binds to the anti codon).

38
Q

What does rRNA do?

A

It joins with proteins to form ribosomes (large and small subunit)
Each subunit is composed of one or more rRNA molecules and a variety of proteins.

39
Q

What is protein synthesis?

A

The process involving the production of a chain of amino acids to form the primary structure of a protein.

40
Q

What occurs during the process of transcription?

A

1) DNA helicase breaks the hydrogen bonds between the bases in a specific region of double stranded DNA in the nucleus.
This causes the strands to separate.

2) RNA polymerase binds to a base called the ‘promoter region’ which determines which way the RNA polymerase faces and which region is used as the template.
It moves along the template strand.

3) RNA nucleotides are activated by the addition of 2 phosphate groups from ATP.
As RNA polymerase moves along the strand, it passes over the DNA bases and forms a ‘complementary mRNA strand’ from free RNA nucleotides in the nucleus.
The strand is bonded by ‘phosphodiester bonds’.

4) As the mRNA strand is produced the 2 DNA strands start to rewind.

5) When a terminator region is reached, the DNA is no longer copied.
The mRNA is ready for the next stage of protein synthesis - ‘translation’

41
Q

What occurs during the process of translation?

A

1) mRNA moves into the cytoplasm through the nuclear pore
2) mRNA attaches to the ribosome (on 5 end moving to 3 end)
3) The first amino acid ‘tRNA complex’ with the correct complementary anticodon binds to the first mRNA codon by hydrogen bonding between complementary bases
4) A second tRNA binds to the vacant mRNA codon (2 at a time)
5) A peptide bond is formed between the 2 adjacent amino acids
6) The ribosome moves along one mRNA codon to the next exposed mRNA codon
7) The empty tRNA molecule is released and returns to the cytoplasm to be activated again
8) This is repeated until a stop codon is reached

42
Q

What is transcription?

A

The formation of mRNA from a section of the template strand of the DNA that corresponds to a gene.

43
Q

What is translation?

A

The production of a polypeptide gene using the sequence of codons on the mRNA.

44
Q

What’s a triplet code?

A

A three-nucleotide codon in a nucleic acid sequence codes for a specific amino acid.

45
Q

What is a codon?

A

A sequence of three bases on the template strand of the DNA or mRNA for one amino acid.

46
Q

What are the properties of the triplet code?

A

It is:
Universal
Non overlapping
Degenerate

47
Q

What does degenerate mean?

A

There is more than one codon for most amino acids.

64 codons for 20 amino acids

48
Q

What does non overlapping mean?

A

Each base is past of only one codon.

49
Q

What does universal mean?

A

The genetic code is the same for almost all organisms

50
Q

How does protein synthesis occur?

A

mRNA formed by transcription from the nuclear DNA passes through pores in the nuclear membrane and attaches to the ribosomes on the rough endoplasmic reticulum.

Specific amino acids are brought to the mRNA my molecules of tRNA which attach to the codons of mRNA by their anticodons.

Adjacent amino acids then join together by peptide bonds to form a polypeptide. This is then released and passes to the Golgi body where is associates with other similar molecules to make a protein.

51
Q

What’s a gene?

A

A sequence of codons on DNA which codes for a specific polypeptide.

52
Q

What’s a chain termination codon?

A

A stop codon which marks the end of a gene/polypeptide.

53
Q

What does tRNA do?

A

It combines with a specific amino acids using energy from ATP.
It carries an amino acid into the ribosome and attaches to appropriate mRNA codons by its anticodon.

Year 12 - Biology (15 decks)

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