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Biology > 2:1:3 Nucleotides and Nucleic Acids > Flashcards

2:1:3 Nucleotides and Nucleic Acids Flashcards

1
Q

What are nucleic acids

A

Polymers that are made up of repeating units (monomers) called nucleotides (e.g. DNA and RNA)

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2
Q

What is the structure of a nucleotide

A
  • Pentose sugar (5 carbons)
  • Nitrogenous base
  • Phosphate group
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3
Q

What are the components of a DNA nucleotide

A
  • Deoxyribose sugar with hydrogen at the 2’ carbon
  • Phosphate group
  • 1 nitrogenous base: adenine (A), cytosine (C), guanine (G) or thymine (T)
  • Double stranded (double helix)
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4
Q

What are the components of a RNA nucleotide

A
  • Ribose sugar with a hydroxyl (OH) group at the 2’ carbon (allows it to be susceptible to hydrolysis allowing it to be the transport molecule as opposed to the storage molecules (DNA))
  • Phosphate group
  • 1 nitrogenous base: adenine (A), cytosine (C), guanine (G) or uracil (U)
  • Single stranded
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5
Q

What are purines

A

The structure of nitrogenous bases with a double ring (e.g. adenine and guanine)

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6
Q

What are pyrimidines

A

The structural formula of nitrogenous bases with a single ring (e.g. cytosine, thymine and uracil)

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7
Q

What are phosphodiester bonds

A

The bond that makes the sugar-phosphate backbone of DNA/RNA and that joins nucleotides together via a condensation reaction between the phosphate group and the pentose sugar of the other nucleotide (one phosphate group and two ester bonds)

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8
Q

What is ATP

A

Adenosine Triphosphate is a phosphorylated nucleotide produced in respiration that are used to transfer energy in all energy requiring processes in cells of organisms, it’s the universal energy currency

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9
Q

What is Adenosine

A

A nucleoside that can be combined with 1,2, or 3 phosphate groups to make adenosine monophosphate (AMP), adenosine diphosphate (ADP), and adenosine triphosphate (ATP)

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10
Q

What is the structure of DNA molecules

A
  • Two polynucleotide strands side by side running in opposite directions (antiparallel)
  • Strands made of alternating deoxyribose sugars and phosphates joined with phosphodiester bonds making the sugar phosphate backbone
  • Phosphodiester bond links 5’ carbon of one molecules to the phosphate of another that is bonded to the 3’ carbon
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11
Q

How is DNA antiparallel

A

On strange runs in the 5’ to 3’ direction, and the other in the 3’ to 5’ direction

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12
Q

How are the two strands of DNA bonded together

A
  • Held together by hydrogen bonds between nitrogenous bases
  • Adenine (A) always makes 2 hydrogen bonds with thymine (T)
  • Guanine (G) always makes 3 hydrogen bonds with cytosine (C)
  • The pairings are called complementary base pairs
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13
Q

What shape is DNA

A

It is the three dimensional shape of a helix

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14
Q

How is DNA purified

A
  • Isolating DNA occurs from the precipitation process
  • Isolating DNA is used in molecular biology
  • Involves the cells and membranes being broken, and enzymes denature and remove proteins in the DNA so it can be formed into an insoluble solid by an organic solvent
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15
Q

Describe the process of DNA purification

A
  • Cut up sample into small pieces and place in a beaker with washing up liquid and water
  • Place beaker in water bath at 60 degrees for 15 mins
  • Cool beaker in ice bath for 5 mins whilst stirring
  • Blend mixture for 5 seconds
  • Filter (with filter paper) the mixture into another beaker
  • Pour 10cm3 filtrate into a test tube and add few drops of protease enzyme and mix
  • Add ice-cold ethanol to the test tube and wait 2 mins
  • Layer of white precipitate containing DNA will sit upon the solution
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16
Q

Why is detergent used in the DNA purification process

A

It disrupts the phospholipids bilayer of the sample cell membranes which releases the DNA

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17
Q

Why is a water bath used in the DNA purification process

A

The heat disrupts the phospholipid bilayer of the sample cell membrane and releases the DNA, as well as denaturing the enzymes released for the cells which would otherwise digest the DNA

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18
Q

Why is an ice-water bath used in the DNA purification process

A

Lowering the temperature prevents the DNA from breaking down

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19
Q

Why is the mixture blended for a short time in the DNA purification process

A

Blending breaks down the cell walls can cell membranes in the sample so further DNA can be released, but only for seconds as otherwise the DNA strands could be broken

20
Q

Why is filtering part of the DNA purification process

A

To remove cell debris and membrane fragments so the filtrate consists of only DNA and it’s associated proteins

21
Q

Why is protease enzyme added in the DNA purification process

A

It denatures and removed the proteins, leaving only the DNA

22
Q

Why is ice cold ethanol added in the DNA purification process

A

Nucleic acids are insoluble in ice cold ethanol so the DNA can form a precipitate at the top of the solution

23
Q

Why does DNA have to replicate before cell division

A

To ensure that the daughter cells from the cell division have full copies of the parental DNA

24
Q

What is semi-conservative replication

A

The way DNA is copied, where in each new DNA molecule, one of the polynucleotide strand is from the original DNA molecule, so the new molecule has conserved half of the original DNA

25
Q

Why does one original DNA strand have to be conserved in semi-conservative replication

A

To ensure there is genetic continuity between generations of cells, so new cells inherit all their genes from the parent cells during cell division, as cells are replaced regularly and have to complete the same function as previously

26
Q

Describe the process of semi-conservative DNA replication

A
  • Occurs in S phase in preparation for mitosis so the number of DNA molecules in parent cells must be doubled
  • Helicase enzyme breaks the hydrogen bonds between base pairs to unwind the double helix
  • The separated strands act as templates for the new strand, where free nucleotides in the nucleus join to their complementary base pair by DNA polymerase enzyme which catalyses the condensation reactions
  • The two strands come together as hydrogen bonds form between the base pairs
27
Q

How does DNA polymerase work

A
  • DNA polymerase enzyme synthesises new DNA strands from the template strands by catalysing condensation reactions between the sugar and phosphate groups
  • It then cleaves (breaks off) the two extra phosphates and uses the energy released to create the phosphodiester bonds between nucleotides
  • Hydrogen bonds form between the base pairs
28
Q

What are Okazaki fragments

A

DNA polymerase travels up the DNA strand from the 3’ to 5’ direction. This is the leading strand which undergoes continuous replication. The lagging strand undergoes discontinued replication where the DNA polymerase waits for the DNA to unzip before producing another strand in fragments (Okazaki)

29
Q

Why must the formation of DNA strands be highly accurate

A

To create exact copies of the parent DNA molecule,

30
Q

What possible mutations can occur during DNA replication

A
  • Bases being inserted in the complementary strand in the wrong order
  • Extra bases being inserted
  • Bases being left out
31
Q

What is the cause of mutations in DNA replication

A

Occurrence of random spontaneous mutations (errors in genetic code)

32
Q

What is a gene

A

A sequence of nucleotides that forms part if a DNA molecule which codes for the production of a specific polypeptide, by controlling protein structure through determining the exact amino acid sequence

33
Q

What determines the shape and behaviour of a protein (polypeptide) molecule

A

Depends on the sequence of amino acids (primary structure of protein molecule)

34
Q

What is the triplet code

A

The sequence of three DNA bases that codes for one amino acid (e.g. CAG codes for the amino acid valine)

35
Q

What are start and stop signals in cells

A

Signals coded by triplet bases that tell the cell where the individual gene starts (by coding for methionine ATG) and stops in order for the DNA to be read correctly and produce the right sequence of amino acids. Stop signals don’t code for amino acids

36
Q

Why is the genetic code non-overlapping

A

Each base in a codon is only read once

37
Q

Why is the genetic code degenerate

A

The are 4 bases, so 64 different possible triplets (4^3=64), but only 20 commonly occurring amino acids, so the code is degenerate as multiple codons code for the same amino acids. The degenerative nature can limit mutations

38
Q

Why is the genetic code universal

A

Every organism uses the same code and the same triplet codes for the same amino acids in all organisms, meaning genetic information is transferable (enabling genetic engineering)

39
Q

What is a codon

A

Each triplet within the mRNA code

40
Q

What is an anti codon

A

Complementary to the codons on mRNA, but are present on tRNA

41
Q

What is protein synthesis

A

Where genes in DNA molecules code for specific sequences of amino acids, that in turn make a specific polypeptide (protein)

42
Q

What are the two stages of protein synthesis

A
  • Transcription
  • Translation
43
Q

What is transcription

A

The first stage of protein synthesis which occurs in the cell nucleus, where the base sequences of genes are copied and transported to ribosomes

44
Q

Describe the process of transcription

A
  • DNA molecule unwinds an DNA polymerase enzyme moves along (hydrogen bonds break between complementary base pairs)
  • Sense strand (5’ to 3’) codes for the protein to be synthesised
  • Complimentary copy of sense strand is made by building a single stranded molecule that acts as the template strand (antisense strand 3’ to 5’)
  • Free RNA nucleotides pair up with complementary bases on the template strand (with thymine being replaced by uracil (U) on the mRNA strand)
  • Sugar-phosphate groups in the RNA nucleotides form phosphodiester bonds by DNA polymerase enzyme forming mRNA molecule
  • Gene is transcribed when mRNA molecule is complete, causing hydrogen bonds between DNA template strand and mRNA strand break and the DNA strand reforms
  • mRNA has a guanine ‘cap’ added to the beginning of the molecule, and a series of 100 adenine molecules ‘tail’ added to the end
  • Splicing occurs and the mRNA strand leaves the nucleus via pores in the nucleic envelope
45
Q

Describe the process of translation

A
  • Occurs in the cytoplasm
  • mRNA attaches to a ribosome which consists of rRNA which is stable so the mRNA is prepared for synthesis
  • Free tRNA molecules in the cytoplasm have triplets of unpaired bases at the anticodon where a specific amino acid can attach
  • tRNA molecules bind with the specific amino acid and bring them to the mRNA molecules so the complementary codons can pair
  • 2 tRNA molecules can fit onto the ribosome at one time
  • A peptide bond is formed via condensation reactions between the amino acids which is catalysed by rRNA
  • Process continues until a stop codon on the mRNA molecule is reached and an amino acid chain is formed
46
Q

What is splicing

A

Removing the non-coding regions (introns) and joining the coding regions (extrons) of the mRNA strand together, before it leaves the nucleus

Biology (25 decks)

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