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Biology: Module 2: Foundations in Biology > Nucleic Acids > Flashcards

Nucleic Acids Flashcards

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1
Q

What are nucleotides?

A

They are monomers of nucleic acids

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2
Q

Describe the structure of a nucleotide

A
  • A pentose monosaccharide sugar with 5 carbon atoms.
  • A phosphate group, PO4-2
  • A nitrogenous base
  • one ring structure or a two ring structure (pyrimidines or purines)
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3
Q

Differences between DNA and RNA nucleotides

A
  • DNA has deoxyribose sugar whereas RNA has ribose sugar. * RNA has uracil rather than thymine.
  • RNA is usually single stranded rather than double.
  • RNA is shorter than DNA.
  • RNA has 3 forms- mRNA, tRNA and rRNA
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4
Q

How many carbon rings are there in purines and name them

A

2 - Adenine and Guanine

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5
Q

How many carbon rings are there in pyrimidines and name them.

A

1 - Cytosine and Thymine

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6
Q

Type of pentose sugar in DNA

A

Deoxyribose

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7
Q

Type of pentose sugar in RNA

A

Ribose

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8
Q

Type of bond in polynucleotides

A

Phosphodiester bonds

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9
Q

How do phosphodiester bonds form in polynucleotides?

A
  • Condensation reactions * between phosphate group on 5th carbon of pentose of nucleotide and hydroxyl group on the 3rd carbon of pentose of other nucleotide.
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10
Q

How do you break phosphodiester bonds?

A

Hydrolysis reactions

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11
Q

What do phosphodiester bonds form?

A

Sugar-phosphate backbone

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12
Q

Describe the structure of DNA (6 marks+)

A
  • DNA nucleotides join to another with phosphodiester bonds forming btwn phosphate group of one nucleotide and the sugar of next. * Forms strand (sugar phosphate backbone)
  • DNA is double stranded held together by hydrogen bonding btwn bases of two strands.
  • purine pairs with pyrimidine, ensuring equal-length ‘rungs’ in the molecule.
  • A to T base pairs . C to G base pairs. = complementary base pairing.
  • two strands are antiparallel: run in opposite directions
  • DNA molecule twists so structure is a double helix.
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13
Q

How to extract DNA from plant material:

A
  1. Grind sample - break cell walls 2. Mix with detergent - break down cell membrane + release cells content
  2. Add salt - break hydrogen bonds btwn DNA + water
    4.Add protease enzymes - break down proteins associated with DNA
    5.Add layer of ethanol on top of sample to precipitate DNA out of solution
  3. Spool out white strand of DNA using glass rod
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14
Q

What does ATP and ADP stand for?

A

Adenosine Triphosphate and Adenosine Diphosphate

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15
Q

Structure of ADP/ATP

A

Phosphorylated nucleotides (add one or more phosphate group)

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16
Q

What do ADP and ATP contain?

A

ribose sugar, adenine base, phosphate groups (ATP = 3, ADP = 2)

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17
Q

How is each strand organised?

A

Phosphate group at one end, hydroxyl group at the other end, 5’3’

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18
Q

How are the strands organised with respect to each other?

A

Antiparallel

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19
Q

Number of hydrogen bonds between A and T

A

2

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20
Q

Number of hydrogen bonds between C and G

A

3

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21
Q

Purine bases

A

A, G

22
Q

Pyrimidine bases

A

C, T (or U)

23
Q

Why is base pairing important?

A

Allows DNA to be copied and transcribed, important for heredity

24
Q

Why is DNA a double helix?

A
  • bases are hydrophobic so sugar-phosphate backbone chains stop bases from coming into contact with water * chains skew themselves to block holes btwn bases but causes atoms to collide with each other
  • more twisting required, twisting of DNA produces double-helix
25
Q

Process of semi-conservative replication

A
  • DNA molecule unwinds from its helical shape, a section at a time catalysed by the enzyme DNA gyrase. * DNA helicase is the enzyme responsible for breaking of the hydrogen bonds between the bases on either strands, causing it to unzip.
  • This exposes the bases on both strands so that DNA replication can occur.
  • Where the two strands separate a Y-shape is formed this is known as a replication fork.
  • The enzyme DNA polymerase is responsible for catalysing the addition of free nucleotides to the two exposed template strands using complementary base pairing in a 3’ to 5’ direction.
  • One stand is known as the leading strand, it is oriented in the 3’ to 5’ direction , towards the replication fork .
  • On the leading strand the nucleotides are added continuously. Whereas with the lagging strand the process has to be done discontinuously using Okazaki fragments.
  • The fragments are then later joined together by DNA ligase.
26
Q

Semi-conservative replication

A

Two new molecules of DNA are produced, each with a strand of old DNA and another strand of new DNA

27
Q

Enzymes involved in semi-conservative replication

A

DNA helicase, DNA gyrase, DNA polymerase, DNA ligase

28
Q

Role of DNA helicase

A

To travel along the DNA backbone and break hydrogen bonds between between complementary base pairs, leading to the strand unzipping

29
Q

Role of DNA polymerase

A

To catalyse the formation of phosphodiester bonds between nucleotides

30
Q

What can occur in semi-conservative replication?

A

Mutations

31
Q

How can mutations occur in semi-conservative replication?

A

Sequences of bases not matching exactly, an incorrect sequence may occur in the newly copied strand

32
Q

Nature of the genetic code

A

Triplet, non-overlapping, degenerate, universal

33
Q

Triplet nature of the genetic code

A

A sequence of three bases called a codon codes for an amino acid

34
Q

Gene

A

Section of DNA that codes for one polypeptide (protein).

35
Q

Universal nature of the genetic code

A

All organisms have the same triplets/codons that code for the same amino acids

36
Q

Degenerate nature of the genetic code

A

Many amino acids have more than one triplet/codon that codes for them.

37
Q

Non-overlapping nature of the genetic code

A
  • Base triplets do not share their bases. * A single codon signals the start of a sequence which makes sure that the codons are read in frame, meaning they start from base 1.
38
Q

What does transcription produce and where does it occur?

A
  • Produces mRNA * Occurs in nucleus
39
Q

Process of transcription

A
  • Transcription occurs in the nucleus of a cell. A section of DNA called a gene unwinds and unzips. Each gene codes for one polypeptide. * The free RNA nucleotides complementary base pair with the exposed DNA bases on the template strand.
  • A length of RNA is created which is a copy of the other DNA strand, called the coding strand.
  • The strand of messenger RNA once created, leaves the nucleus through a nuclear pore
40
Q

What does translation produce and where does it occur

A
  • Produces proteins (polypeptides) * Occurs on ribosomes attached to the RER
41
Q

Process of translation

A
  • After leaving the nucleus through a nuclear pore mRNA attaches to a ribosome on the rough endoplasmic reticulum. * Two codons on the mRNA strand are exposed by the ribosome at a time.
  • Transfer RNA brings amino acids to the ribosome .
  • The tRNA molecule has a binding site made up of three bases which are specific to particular amino acid .
  • The tRNA molecule also has three exposed bases called anticodons , this is complementary to the codon on the mRNA strand .
  • Temporary hydrogen bonds form between the codon and the anticodon.
  • As two amino acids brought close to one another by adjacent molecules an enzyme catalyses the formation of peptide bond between them.
  • Energy in the form of ATP is required for this process.
  • Eventually a stop codon is reached on the mRNA strand which signals the end of the polypeptide, which is then released.
  • The polypeptide can then fold into its 3D shape with the help of chaperone proteins.
  • The polypeptide breaks loose from the ribosome and mRNA is broken down and recycled.
42
Q

How can multiple identical polypeptides be formed at once?

A

Many ribosomes can follow on the mRNA behind the first

43
Q

Role of mRNA

A

To carry the sequence of bases making up the gene in the DNA to the ribosomes where it can be translated

44
Q

Role of tRNA

A

To carry the correct amino acids to the ribosomes in translation

45
Q

Role of rRNA

A

To maintain the structural stability of the protein synthesis sequence and to catalyse the reaction

46
Q

Role of DNA gyrase

A

Unwinds the double helix structure of the DNA

47
Q

Role of DNA ligase

A

Catalyses the joining of Okazaki fragments on the lagging strand.

48
Q

What are the three main types of activities a cell requires energy?

A
  • Synthesis - large molecules such as proteins * Transport - pumping molecules or ions across cell membranes by active transport * Movement - protein fibres in muscle cells that cause muscle contraction
49
Q

What does phosphorylate mean?

A

To add one or more phosphate groups

50
Q

Describe the Cycle of ATP

A
  • ATP provides energy for chemical reactions in the cell. * ATP is synthesised from ADP and inorganic phosphate (Pi ) using the energy from an energy - releasing reaction , e.g. the breakdown of glucose in respiration. (condensation reaction)
  • The ADP is phosphorylated to form ATP and a phosphate bond is formed. Energy is stored in the phosphate bond.
  • When this energy is needed by a cell, ATP is broken back down into ADP and Pi (hydrolysis reaction-add water).
  • Energy is released from the phosphate bond and used by the cell.

Biology: Module 2: Foundations in Biology (10 decks)

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