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AS Biology > Module 2.3 - Nucleotides and nucleic acids > Flashcards

Module 2.3 - Nucleotides and nucleic acids Flashcards

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1
Q

What is a nucleotide made from?

A

> A pentose sugar (sugar with 5 carbon atoms).
A nitrogenous base.
A phosphate group.

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2
Q

What is a purine base?

A

Contains 2 carbon-nitrogen rings joined together.

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3
Q

What is a pyrimidine base?

A

Only has one 1 carbon-nitrogen ring. So a pyrimidine base is smaller than a purine base.

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4
Q

What nitrogenous bases are purines?

A

Adenine and guanine.

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5
Q

What nitrogenous bases are pyrimidines?

A

Cytosine and thymine.

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6
Q

What is the difference in sugars in RNA and DNA?

A

In DNA, the pentose sugar is called deoxyribose whereas, in RNA contains nucleotides with a ribose sugar.

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7
Q

What base replaces thymine in RNA?

A

Uracil.

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8
Q

What does it mean to phosphorylate a nucleotide?

A

You add one or more phosphate groups to it.

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9
Q

What does ATP stand for and what does it contain?

A

Stands for adenosine triphosphate contains the base adenine, the sugar ribose and three phosphate groups.

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10
Q

How does ATP release energy?

A

Energy is stored in the phosphate bond and when this energy is needed by a cell, ATP is broken back down into ADP and inorganic phosphate.

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11
Q

How do nucleotides join together to form polynucleotides?

A

The nucleotides join up between the phosphate group of one nucleotide and the sugar of another, this forms a phosphodiester bond. The chain of sugar-phosphate backbone.

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12
Q

Describe the structure of the DNA double helix?

A

2 DNA polynucleotide strands join together by hydrogen bonds between the bases and each base pairs up with their complementary base. Two antiparallel polynucleotide strands twist to form the DNA double-helix.

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13
Q

What does adenine pair with?

A

Thymine.

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14
Q

What does cytosine pair with?

A

Guanine.

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15
Q

How many hydrogen bonds are between A-T?

A

2

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16
Q

How many hydrogen bonds are between C-G?

A

3

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17
Q

How does DNA self replicate?

A

> DNA helicase (an enzyme) breaks the hydrogen bonds between the polynucleotide strands and the helix unzips to form 2 single strands.
Each original strand acts as a template for a new strand. Free floating DNA nucleotides join to the exposed bases on each original template strand by complementary base pairing - A with T and C with G.
The nucleotides of the new strand are joined together by the enzyme DNA polymerase. This forms the sugar-phosphate backbone. Hydrogen bonds form between the bases on the original and new strand. The strands twist to form a double-helix.
Each new DNA molecule contains 1 strand from the original DNA molecule and 1 new strand.

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18
Q

What is this type of replication called and why?

A

Semi-conservative replication because half of the strands in each new DNA molecule are from the original piece of DNA.

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19
Q

Why is it important that DNA replication is accurate?

A

To make sure genetic information is conserved (stays the same) each time the DNA in a cell is replicated.

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20
Q

What is a mutation?

A

A mutation is any change to the DNA base sequence.

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21
Q

What is the effect of a mutation?

A

Mutations don’t always have an effect, but they can alter the sequence of amino acids in a protein. This can cause an abnormal protein to be produced, the abnormal protein might function better than the normal protein - or it might not work at all.

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22
Q

What is a gene?

A

A gene is a sequence of DNA nucleotides that codes for a polypeptide.

23
Q

What part of a polypeptide’s structure does the sequence of amino acids make up?

A

Forms the primary structure of a protein.

24
Q

What is a “triplet”?

A

In a gene each amino acid is coded for by a sequence of 3 bases called a triplet.

25
Q

Where are ribosomes are found in a cell?

A

Cytoplasm and the rough endoplasmic reticulum.

26
Q

What is transcription?

A

DNA is too large to move out of the nucleus, so a section is copied into mRNA.

27
Q

What are three adjacent bases called?

A

Codon.

28
Q

Where is mRNA made?

A

The nucleus.

29
Q

What does mRNA stand for?

A

Messenger RNA.

30
Q

What does mRNA do?

A

It carries the genetic code from the DNA in the nucleus to the cytoplasm, where it’s used to make a protein. This process is called translation.

31
Q

What does tRNA stand for?

A

Transfer RNA.

32
Q

Where is tRNA found?

A

In the cytoplasm.

33
Q

What is tRNA structure?

A

It has an amino acid binding site at one end and a sequence of 3 bases at the other end called an anticodon.

34
Q

What does tRNA do?

A

It carries the amino acids that are used to make proteins to the ribosomes during translation.

35
Q

What does rRNA stand for?

A

Ribosomal RNA.

36
Q

What does rRNA form?

A

Forms the 2 subunits in a ribosome (along with proteins).

37
Q

What does the rRNA do?

A

The ribosome moves along the mRNA strand during protein synthesis. The rRNA in the ribosome helps to catalyse the formation of peptide bonds between the amino acids.

38
Q

What is the genetic code?

A

The genetic code is the sequence of base triplets (codons) in DNA or mRNA which codes for specific amino acids.

39
Q

What does it mean that the genetic code is ‘non-overlapping’?

A

Each base triplet is read in sequence, separate from the triplet before it and after it and base triplets don’t share their bases.

40
Q

What does it mean that the genetic code is degenerate?

A

There are more possible combinations of triplets than there are amino acids (20 amino acids but 64 possible triplets). This means that some amino acids are coded for by more than one base triplet.

41
Q

What do start and stop signals/codons do and where are they found?

A

Some triplets are used to tell the cell when to start and stop production of the protein and are found at the beginning and end of the gene.

42
Q

Why is the genetic code described as universal?

A

Because the same specific base triplets code for the same amino acids in amino acids in all living things.

43
Q

Describe the first stages of proteinsynthesis - transcription up to where the mRNA molecule is starting to form?

A

1) Starts with RNA polymerase (an enzyme) attaching to the DNA double helix at the beginning of the gene.
2) The hydrogen bonds between the 2 DNA strands in the gene break, separating the strands and the DNA molecule uncoils at that point.
3) One of the strands is then used as a template to make an mRNA copy.
4) The RNA polymerase lines up free RNA nucleotides alongside the template strand. Complementary base pairing means that the mRNA strand ends up being a complementary base copy of the DNA template strand.
5) Once the RNA nucleotides have paired up with their specific bases on the DNA strand they’re joined together, forming an mRNA molecule.

44
Q

Describe the first stages of proteinsynthesis - transcription from where the mRNA molecule is starting to form to when it leaves the nucleus?

A

1) The RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand.
2) The hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into a double-helix.
3) When RNA polymerase reaches a stop codon it stops making mRNA and detaches from the DNA.
4) The mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where the next stage of protein synthesis takes place.

45
Q

Where does the 2nd stage of protein synthesis -translation occur?

A

Ribosomes in the cytoplasm.

46
Q

Describe the stages of translation?

A

1) mRNA attaches to a ribosome and tRNA molecules carry amino acids to the ribosome.
2) A tRNA molecule’s anticodon attaches to the start codon on the mRNA molecule.
3) A 2nd tRNA molecules attaches itself to the next codon on the mRNA in the same way.
4) rRNA in the ribosomes catalyses the formation of a peptide bond between the 2 amino acids attached to the tRNA molecules. This joins the amino acids together.
5) The 1rst tRNA molecule moves away, leaving the amino acid behind.
6) A third tRNA molecule binds to the next codon on the mRNA and its amino acid binds to the 1rst 2 and the 2nd tRNA molecule moves away.
7) This process continues, producing a chain of linked amino acids (polypeptide chain) until there’s a stop codon on the mRNA molecule.
8) The polypeptide chain moves away from the ribosome and translation is complete.

47
Q

How does the anticodon on the tRNA molecule attach itself to the start codon on the mRNA?

A

The anticodon on the tRNA molecule is complementary to the start codon on the mRNA (complementary base pairing).

48
Q

What practical/reaction can you use to purify DNA?

A

A precipitation reaction.

49
Q

Outline the steps/method of the precipitation reaction to purify DNA?

A

1) Break up cells in your sample.
2) Make up a solution of detergent, salt and distilled water.
3) Add the broken-up cells to a beaker with the detergent solution and incubate the beaker in a water bath at 60 degrees for 15 minutes.
4) Once incubated, put the beaker in an ice bath to cool the mixture down and the filter it and transfer a sample of your mixture to a clean boiling tube.
5) Add protease enzymes which will break down proteins in the mixture such as those bound to the DNA.
6) Slowly dribble some cold ethanol down the side of the tube so it forms a layer on top of the DNA-detergent mixture.
7) Leave the tube for a few minutes and the DNA will form a white precipitate which you can remove from the tube using a glass rod.

50
Q

In the precipitation reaction what enzymes should you add to break down RNA in the mixture?

A

Dnase enzymes.

51
Q

In the precipitation reaction what does the detergent in the mixture do?

A

Breaks down the cell membranes.

52
Q

In the precipitation reaction what does the salt in the mixture do?

A

The salt binds to the DNA and causes it to clump together.

53
Q

In the precipitation reaction what does the high temperature in the mixture do?

A

Should stop enzymes in the cells form working properly and breaking down the DNA.

AS Biology (12 decks)

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