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OCR Biology A level New Spec > 2.1.3 Nucleotides and nucleic acids > Flashcards

2.1.3 Nucleotides and nucleic acids Flashcards

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1
Q

what is a nucleotide?

A

it is a bio molecule and a monomer that can join to make the polymer nucleic acid - DNA and RNA

  • all nucleotides contain: Carbon, Hydrogen, Oxygen, Nitrogen, and Phosphate
  • consists of a pentose sugar, phosphate group and a nitrogenous base
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2
Q

why are nucleotides important?

A
  1. they r the monomers that make up DNA/RNA(stores genetic info and how to make proteins)
  2. can become phosphorylated nucleotides that make up ADP and ATP(energy currency of the cell)
  3. may be the components of coenzymes e.g. adenine nucleotides r components of coenzyme NADP
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3
Q

what is a DNA nucleotide and draw it

A
  • contains a deoxyribose sugar as the pentose sugar, a nitrogenous base that can be either (adenine(A), thymine (T), cytosine (C), and guanine (G)) and a phosphate group

draw here

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4
Q

what is a RNA nucleotide and draw it

A
  • contains a ribose sugar as its pentose sugar, a nitrogenous base that is either; adenine (A), Cytosine (C), Guanine (G) or Uracil (U), and a phosphate group
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5
Q

how can u classify the nitrogenous bases? an what do they mean?

A

there r two types of bases: purines or pyrimidines
purines include: Adenine/Guanine
pyrimidines: Cytosine/Thymine/Uracil

difference is in the struc - purines are 2 carbon-nitrogen rings joined together and pyrimidines r 1 C-N ring so the latter is smaller than the former

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6
Q

what is ADP and ATP

A

they are phosphorylated nucleotides - both containing base adenine and sugar ribose

  • to phosphorylate a nucleotide u add a phosphate group
  • ADP(adenosine diphosphate) - 2 phosphate groups
  • ATP (adenosine triphosphate) - 3 phosphate groups
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7
Q

how is ATP used and released

A

energy released from glucose is used to make ATP and then ATP is broken down to release energy for cells to use

  • ATP is synthesised from ADP and inorganic phosphate (Pi)
  • ADP is phosphorylated to form ATP and a phosphate bond is formed using the energy from glucose
  • energy is stored in the phosphate bond and when needed will break down to release energy
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8
Q

what are many nucleotides joined together called

A

polynucleotides

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9
Q

what is the structure of a polynucleotide and how do nucleotides bond

draw diagram

A

nucleotides join between the phosphate group of one and the sugar of another to form a phosphodiester bond (where 1 phosphate group makes 2 ester bonds on both sides)
- the chain of sugars and phosphates is known as the sugar-phosphate backbone
diagram

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10
Q

what is the structure of DNA

A
  • it is a polymer consisting of nucleotide monomers
  • each nucleotide consists of 1 pentose (deoxyribose) sugar, 1 phosphate group, and A/C/T/G as their nitrogenous base
  • nucleotides joined by phosphodiester bonds
  • composed of 2 polynucleotide chains joined to forma double helix shape
  • strand join via H bonds between bases (complementary base pairing): A-T and G-C
  • two H bonds form between A and T and 3 form between G and C
  • the strands r anti-parallel (run in oppo directions)
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11
Q

what is complementary base pairing

A

A forms 2 H bonds to T
C forms 3 H bonds to G

(or inRNA A forms 2 H bonds to U)

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12
Q

explain the struc and also draw the anti-parallel sugar-phosphate backbone

A

the anti parallel sugar phosphate backbone is formed by 2 polynucleotides running in opposite directions w the nucleotides joined by phosphodiester bonds and the strands to each other by Hbonds

  • the oppo direction refers to direction of 3rd/5th Carbon molecule on the deoxyribose are facing
  • 5’ end is when phosphate is attached to 5th carbon atomof sugar
  • 3’end is when phosphate is attached to 2rd C atom of sugar
  • molecule is stable af

diagram

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13
Q

how is DNA arranged in a eukaryotic cell

A
  • maj of DNA in nucleus
  • each molecule of DNA wound around proteins called histones into chromosomes
  • each chromosome is 1 molecule of DNA
  • also loops of DNA in mitochondria and chloroplasts
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14
Q

how is DNA arranged in a prokaryotic cell

A
  • DNA is in a loop in cytoplasm(no nucleus)
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15
Q

why and when does DNA replicate?

A
  • each cells makes copies of its DNA so that the when cell division occurs each daughter cell has the same original amount of DNA as the parent cell - aka it is genetically identical
  • it replicates during interphase
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16
Q

what is DNA replication also known as

A

semi conservative replication

17
Q

how does semi conservative replication work (show the direction by drawing diagram)

A
  1. DNA molecule unwinds, double helix untwists (gyrase enzyme)
  2. DNA unzips (catalysed by DNA helicase) - H bonds break between polynucleotide strands leaving exposed nucleotide bases
  3. free phosphorylated nucleotides bond to exposed bases by complementary base pairing
  4. DNA polymerase catalyses addition of new nucleotide bases in the 5’ to 3’ direction to the strands of DNA using unzipped DNA as temple
  5. leading strand is synthesised continously
  6. lagging strand is in fragments (later joined by ligase enzymes)

product is 2 DNA molecules - identical to each other and to the parent molecule - each contains 1 new strand and 1 old strand - making it semi-conservative replication

diagram

18
Q

what is a mutation

A

a random change to the DNA base sequence - inserting wrong nucleotide

19
Q

what r the effects of a mutation during DNA replication

A

can be advantageous e..g white coat in winter can help conceal
or disadvantageous - e..g make a faulty enzyme
or just neutral e..g can roll your tongue

20
Q

name differences between RNA and DNA molecule

A

RNA sugar is pentose not deoxyribose
RNA nitrogenous bases r Uracil and not Thymine
RNA is a single stranded molecule
RNA is shorter
there r 3 forms of RNA: m(messenger)RNA, r(ribosomal)RNA, and t(transfer)RNA

21
Q

define a gene

A

a gene is a length of DNA that codes for a polypeptide or for a length of RNA that is involved in regulating gene expression

22
Q

how do genes code for a polypeptide

A

each gene contains a sequence of DNA base triplets that determines the aa sequence or primary struc of a protein/polypeptide
- (aka every 3 nucleotides codes for a specific aa - the sequence of the triplets determines which one)

23
Q

why is the gene important for proteins

A
  • determines it primary struc which will in turn determine its ultimate final struc/shape (tertiary/quatenary)
  • e..g shape of active site of enzyme most be complementary of substrate to work
  • antibodies must to complementary to the antigens on pathogens it attacks
24
Q

why is mRNA necessary

A

the original instructions for making proteins cannot be removed from the nucleus so it has to be transcribed into mRNA to be transferred to ribosomes to make proteins
- the base triplets r now called codons

25
Q

what happens at the ribosome when mRNA reaches it

A

the mRNA is translated and then the protein is assembled correctly from aas

26
Q

what is the nature of the genetic code (sequence of base triplets/codons that codes for amino acids in DNA and mRNA

A
  1. triplets - each sequence of 3 bases (base triplet) codes for a specific amino acid in a gene
  2. non-overlapping - base triplets do not share their bases hence each base triplet is read in sequence
  3. degenerate - most amino acids can be coded for by multiple base triplets - reduces the effect of point mutations
  4. universal - same specific base triplets code for the same aas in all living things e.g UAU codes for tyrosine in all organisms
27
Q

describe the different types of RNA and their roles

A
  1. mRNA - is transcribed at the nucleus and translated at the ribosomes to make proteins
    - it carries the genetic code in codons - each codon codes for an amino acid and is a single polynucleotide strand
  2. tRNA - transfer RNA is also a single polynucleotide strand in a clover shape (by H bonds) -
    - every tRNA molecule has an anticodon at one end - a sequence of 3 bases which is complementary to a codon
    - at the other end is an aa binding site
    - found in cyto and involved in translation and carries aa s used to make proteins to the ribosomes
    - made in the nucleolus
  3. rRNA
    - helps to catalyse formation of peptide bonds between the aas at the ribosome
28
Q

describe the process of transcription

A
  1. a gene unwinds and unzips
  2. H bonds break between the two strands - complementary nucleotide bases break
  3. enzyme RNA polymerase catalyses formation of temporary H bonds between RNA nucleotides and complementary unpaired DNA bases w complementary base pairing rules
  4. DNA strand is called template strand
  5. length of RNA that is complementary to part of the gene on the DNA template strand is produced - it is known as the coding strand
  6. mRNA now passes thru nucleus to ribosomes in cyto
29
Q

describe the process of translation

A
  1. tRNA molecules have anticodons which binds by temp H bonds to complementary codons on the mRNA molecule - it has an amino acid that the codon codes for attached to the other end
  2. as ribosome moves along mRNA it reads the code and when 2 aas r next to each other it is joined by peptide bonds (rRNA catalyses this) - the first tRNA molecule then moves away leaving its aa behind
  3. continues until a stop codon is read on the mRNA
  4. aa sequence for polypeptide depends on base triplets on DNA molecule (gene)
  5. after polypeptide is assembled mRNA breaks down to be recycled
  6. polypeptide is processed into final shape
30
Q

how can you extract DNA?

A
  1. break up cells in sample (blender)
  2. use solution of detergent and salt and distilled water to add to the broken cells in beaker
  3. incubate beaker in water bath (60degrees 4 15mins)
  4. detergent breaks down membranes and salt causes dna to clump together and temp breaks down enzymes
  5. put beaker in ice bath to cool down and then filter mixture into a boiling tube
  6. add protease to filtered mixture (break down proteins in DNA)
  7. dribble cold ethanol down tube so it forms a layer on top
  8. leave tube for few mins and it will form a white precipitate !! this is the DNA

OCR Biology A level New Spec (28 decks)

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