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OCR Biology AS Level > 2.3 - Nucleic Acids > Flashcards

2.3 - Nucleic Acids Flashcards

1
Q

What are NUCLEOTIDES made up of (3) ?

A
  1. FIVE-CARBON SUGAR (pentose)
  2. PHOSPHATE GROUP
  3. NITROGENOUS BASE (Adenine,Cytosine,Thymine,Guanine)
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2
Q

What are nucleotides monomers of?

A

Nucleic acids, DNA and RNA.

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3
Q

What is the nucleotide pentose sugar in RNA?

What is the nucleotide pentose sugar in DNA?

A

The nucleotide pentose sugar in RNA is RIBOSE.

The nucleotide pentose sugar in DNA is DEOXYRIBOSE.

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4
Q

What are PHOSPHORYLATED NUCLEOTIDES?

A

Nucleotides that have more than one phosphate group.

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5
Q

Give 2 examples of phosphorylated nucleotides.

A

ADP (adenosine diphosphate)

ATP (adenosine triphosphate)

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6
Q

What is ATP?

A

An energy-rich product of most energy-releasing biochemical pathways, and it is used to drive most energy-requiring metabolic processes in cells.

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7
Q

What is AMP?

A

Adenosine monophosphate

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8
Q

What else, other than form the monomers of nucleic acid and become phosphorylated, can nucleotides do (2) ?

A
  1. help REGULATE many METABOLIC PATHWAYS (e.g. by ATP, ADP and AMP)
  2. become components of many coenzymes, e.g. adenine nucleotides are components of the coenzyme NADP (for photosynthesis), NAD (for respiration), FAD and Coenzyme A (respiration).
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9
Q

What is DNA in terms of polymers and monomers?

A

A polymer made up of many repeating monomeric units called nucleotides.

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10
Q

What does a molecule of DNA consist of?

A

TWO POLYNUCLEOTIDE STRANDS

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11
Q

What are polynucleotides?

A

A large molecule containing many nucleotides.

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12
Q

Why are DNA described as “anti-parallel”?

A

The two strands run in opposite directions.

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13
Q

What is the covalent bond between the sugar residue and the phosphate group in a nucleotide called?

A

PHOSPHODIESTER BOND

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14
Q

Describe how phosphodiester bonds are broken and formed in DNA.

A

Condensation reaction BREAKS the phosphodiester bond by forming water via the -OH of the deoxyribose and the -H of the phosphate group or the -H of the thymine.

Hydrolysis reaction FORMS the phosphodiester bond by adding H2O.

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15
Q

Which bases are PURINES?

How many rings do PURINES have?

A

Adenine or Guanine.

Purines have TWO rings.

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16
Q

Which bases are PYRIMIDINES?

How many rings do PYRIMIDINES have?

A

Thymine or Cytosine

Pyrimidines have ONE ring.

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17
Q

Which bases pair with which?

A

Adenine pairs with Thymine.

Cytosine pairs with Guanine.

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18
Q

How many hydrogen bonds are formed between the pairing of adenine and thymine?

A

TWO hydrogen bonds

19
Q

How many hydrogen bonds are formed between the pairing of cytosine and guanine?

A

THREE hydrogen bonds

20
Q

What gives the equal-sized ‘rungs’ on the DNA ladder?

A

The pairing of a PURINE and a PYRIMIDINE.

21
Q

What is the structure of DNA known as?

Why is DNA structured in this way?

A

The structure of DNA is known as a DOUBLE-HELIX.

This gives the molecule STABILITY.

22
Q

What allows the molecules to unzip for protein synthesis?

A

Hydrogen bonds

23
Q

When the corresponded pairs are joined, what scientific term do we give this?

A

COMPLEMENTARY BASE PAIRING

24
Q

What is the upright part of the large DNA molecule that resembles a ladder formed by?

A

The SUGAR-PHOSPHATE BACKBONES of the antiparallel polynucleotide strands.

25
Q

Describe 5’ prime and 3’ prime in DNA.

A

The 5’ end of the molecule is where the phosphate group is attached to the 5th carbon atom.

The 3’ end is where the phosphate group is attached to the 3rd carbon atom of the deoxyribose sugar.

26
Q

What do the rungs of the DNA ladder consist of?

A

The complementary base pairs, joined by hydrogen bonds.

27
Q

What is the purpose of the SUGAR-PHOSPHATE BACKBONES?

A

To give the DNA molecule STABILITY.

28
Q

How is DNA organised in eukaryotic cells (3)?

A
  1. The majority of the DNA content (genome) is in the nucleus.
  2. Each large molecule of the DNA is tightly wound around special HISTONE proteins into CHROMOSOMES. Each chromosome is therefore one molecule of DNA.
  3. There is also a loop of DNA, WITHOUT the histone proteins, inside mitochondria and chloroplasts.
29
Q

How is DNA organised in prokaryotic cells (2)?

A
  1. DNA is in a loop and is within the cytoplasm, NOT enclosed in a nucleus.
  2. It is NOT wound around histone proteins. They’re described as naked.
30
Q

How is DNA organised in viruses?

A

Viruses that contain DNA also have it in the form of a loop of Naked DNA.

31
Q

Explain the extraction and purification of DNA by precipitation.

A
  1. Macerate the tissue of the fruit.
  2. Add a strong detergent
  3. Add ethanol so that the DNA precipitates out of the solution.
  4. The DNA can then be further purified by removal of unwanted salts and can then be concentrated.
32
Q

Describe the FIRST step for DNA SEMI-CONSERVATIVE REPLICATION (2).

A

To make a new copy of itself, each DNA molecule:
1. UNWINDS - the double helix is unravelled, a bit at a time to prevent supercoiling, catalysed by DNA Gyrase.

  1. UNZIPS - hydrogen bonds between the nucleotide bases are broken. This is catalysed by DNA Helicase, and results in two single strands of DNA with EXPOSED nucleotide bases.
33
Q

Describe the SECOND step for DNA SEMI-CONSERVATIVE REPLICATION.

A
  1. The phosphorylated nucleotides, present in the nucleoplasm within the nucleus, are bonded to the exposed bases, following complementary base-pairing rules.
  2. The enzyme DNA Polymerase catalyses the addition of new nucleotide bases, in the 5’ to 3’ direction to the single strands of DNA; it uses each single strand of unzipped DNA as a TEMPLATE.
  3. The leading strand is synthesised continuously, whereas the lagging strand is in fragments that are later joined, catalysed by DNA Ligase.
  4. Hydrolysis of the activated nucleotides, to release the extra phosphate groups, supplies the energy to make phosphodiester bonds between the sugar residue of one nucleotide and the phosphate group of the next molecule.
34
Q

What is the final product in DNA replication?

A

TWO DNA molecules, identical to each other and the PARENT molecule.

35
Q

Why is the DNA replication known as SEMI-CONSERVATIVE REPLICATION?

A

Each of the molecules contains one OLD (original) strand and one NEW strand.

36
Q

What are MUTATIONS?

A

Errors occurring during DNA replication, where the wrong nucleotide may be inserted.

37
Q

What is the probability of a mutation happening?

A

1 in 10^8 base pairs.

38
Q

What are different versions of a particular gene called?

A

ALLELES or GENE VARIANTS.

39
Q

Compare DNA and RNA in terms of structure.

A

RNA: the sugar molecule in each nucleotide is RIBOSE
DNA: the sugar molecule is DEOXYRIBOSE

RNA: The nitrogenous base URACIL, which is a pyrimidine, replaces the pyrimidine base THYMINE
DNA: The pyrimidine base is THYMINE

RNA: The polynucleotide chain is usually single-stranded
DNA: The polynucleotide chain has more than one strand.

RNA: The polynucleotide chain is shorter
DNA: The polynucleotide chain is longer

There are three forms of RNA: messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA)

40
Q

Describe and explain the nature of the genetic code, using three keywords. (3)

A
  1. The genetic code is near UNIVERSAL because in almost ALL living organisms, the same triplet of DNA bases code for the SAME amino acid.
  2. The genetic code is described as being DEGENERATE, because, for all amino acids, except methionine and tryptophan, there is MORE THAN ONE base triplet. This may reduce the effect of point mutation, as a change in one base of the triplet could produce another base triplet that still codes for the same amino acid.
  3. The genetic code is NON-OVERLAPPING, and it is read starting from a fixed point in groups of three bases. If a base is added or deleted then it causes a frameshift, as every base triplet after that and hence every amino acid coded for, is changed.
41
Q

What are the two stages of DNA Polypeptide Coding called?

A
  1. TRANSCRIPTION

2. TRANSLATION

42
Q

Describe the TRANSCRIPTION stage.

A
  1. A gene unwinds and unzips, catalysed by DNA Gyrase and DNA Helicase.
  2. Hydrogen bonds between complementary nucleotide bases break.
  3. The enzyme RNA Polymerase catalyses the formation of temporary hydrogen bonds between RNA nucleotides and their complementary unpaired DNA bases. (U pairs with A). This DNA strand is called the TEMPLATE strand.
  4. A length of RNA that is COMPLEMENTARY to the template strand of the gene is produced. This DNA strand is called the CODING strand.
  5. The mRNA now passes out of the nucleus, through the nuclear envelope, and attaches to a ribosome.
43
Q

Describe the TRANSLATION stage.

A
  1. tRNA molecules, which have a specific amino acid, and an anticodon, bring the amino acids together. They allow the anticodon to bind with the temporary hydrogen bonds COMPLEMENTARY to the codon on the mRNA molecule.
  2. As the ribosome moves along the length of mRNA, it reads the code, and when two amino acids are adjacent to each other, a PEPTIDE BOND is formed between them.
44
Q

Describe the investigation of using methyl green-pyronin stain to show the distribution of DNA and RNA within cells.

A
  1. Use a clean sharp scalpel or razor blade and cut thin longitudinal sections of the tip of the fixed root. Each section should be about 3mm long.
  2. Place the sections on a microscope slide and cover with methyl green-pyronin stains for 30mins.
  3. Use a pipette to remove the stain, and then add distilled water to the root tips.
  4. Change the water several times to wash the root-tip sections.
  5. Add a drop of distilled water and a coverslip.
  6. Observe cells in the sections under low power then high power.
  7. You should see DNA stained blue-green in the cells’ nuclei and RNA stained red in the cytoplasm.

OCR Biology AS Level (13 decks)

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