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OCR Biology A Level > 2.1.3 Nueclotides and Nucleic Acids > Flashcards

2.1.3 Nueclotides and Nucleic Acids Flashcards

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1
Q

What are the two types of nucleic acid?

A
  • DNA (deoxyribonucleic acid)
  • RNA (ribonucleic acid)
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2
Q

What does the base sequence of DNA code for?

A

The sequence of amino acids in a polypeptide

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3
Q

What monomers are nucleic acids, and what components are these monomers made from?

A

Nucleotides

  • phosphate
  • pentose sugar
  • organic nitrogenous base
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4
Q

How do the pentose sugars used differ between DNA and RNA?

A
  • DNA has pentose sugar deoxyribose (Missing an oxygen)
  • RNA has pentose sugar ribose
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5
Q

Explain why bases are referred to as ‘organic’ and ‘nitrogenous’ and name the 5 different bases

A

Organic - contain carbon
Nitrogenous - contain nitrogen

Types of base
- adenine
- thymine
- cytosine
- guamine
- uracil

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6
Q

How do DNA and RNA differ in the bases they contain?

A

DNA: A,T,G,C
RNA: A,U,G,C

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7
Q

What do nucleotides link together to form, and how are these created?

A

Polynucleotides

  • formed by condensation reactions
  • phosphate group at the 5thcarbon of pentose sugar (5’) forms covalent bond with OH group at 3rd carbon of pentose sugar (3’) of adjacent nucleotide
  • phosphodiester bond formed between nucleotides
  • sugar + phosphate form strong phosphate-sugar backbone
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8
Q

Give key aspects of DNA

A
  • double stranded
  • polynucleotide strands run antiparralel - joined by hydrogen bonds
  • base pairing - A+T (2 H bonds), G+C (3 H bonds)
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9
Q

Who proposed this structure of DNA?

A

Watson and Crick

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10
Q

What is the difference between purines and pyrimidines, and which bases are which?

A

Purines - larger, 2 sections
- adenine
- guanined

Pyrimidines - smaller, 1 section
- thymine
- cytosine

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11
Q

What is chargaff’s rule?

A
  • A must pair with T
  • G must pair with C
  • equal amounts of adenine and thymine
  • equal amounts of guanine and cytosine
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12
Q

Compare DNA and RNA

A

Pentose sugar: DNA = deoxyribose, RNA = ribose
Pyrimidine base: DNA = C or T, RNA = C or U
Purine base: DNA = A or G, RNA = A or G
No. polynucleotide strands: DNA = 2, RNA = 1
No. nucleotides: DNA = 100,000s, RNA = 100s
Types of molecule: DNA = 1, RNA = 3 - rRNA, tRNA,mRNA

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13
Q

What is DNA replication and where does it occur?

A

DNA is replicated in the nucleus

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14
Q

Explain the steps of semi-conservative DNA replication

A
  1. DNA unwinds ( gyrase enzyme)
  2. Strands speperate (helicase enzyme breaks H bonds)
  3. Free DNA nucleotides pair with complmentory bases
  4. H bonds form between pairs
  5. sugar phosphate backbone formed (DNA polymerase enzyme)
  6. Two identical copies of DNA formed
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15
Q

What happens if replication errors occur?

A
  • daughter cells dont revieve genetic information
  • proteins don’t function or aren’t made
  • new cells don’t function or aren’t made
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16
Q

What is meant by semi-conservsative replication?

A

Each DNA molecule consists of one old strand and one new strand

17
Q

Name 3 main models put forward for DNA replication

A
  • conservative
  • semi-conservative
  • dispersive
18
Q

Explain how Meselson and Stahl proved the semi-conservative model

A
  • grew E. coli bacteria in a medium with heavy nitrogen (15N)
  • transferred the bacteria to a medium with light nitrogen (14N)
  • took DNA samples at intervals after the transfer
  • Separated the DNA samples using centrifugation
  • after one generation: found DNA containing both heavy and light nitrogen
  • after two generations: observed both hybrid and light DNA.
19
Q

What is DNA synthesis and where does it occur?

A

Making proteins in the nucleus and ribosomes

20
Q

Why is transcription and mRNA needed?

A
  • DNA is too large to leave the nucleus
  • DNA is transcribed into mRNA which leaves through nuclear pores
  • mRNA attaches to ribsome for translation
21
Q

Explain the steps of transcription

A
  1. DNA unwinds in region coding for a gene
  2. Hydrogen bonds broken between DNA bases, so strands seperate (RNA polymerase)
  3. Bases of free RNA nucleotides bond with bases of DNA nucleotides - makes template strand on DNA
  4. Phosphodiester bonds form betwwen nucleotide bases (RNA polymerase enzyme)
  5. mRNA copy seperates from template and leaves nucleus via nuclear pores
22
Q

Explain the key aspects of ribosomal RNA

A
  • composed of two subunits - one large and one small
  • subunits composed of proteins + rRNA
  • ribosome holds mRNA in place while it is translated
23
Q

Explain the key aspects of transfer RNA

A
  • made from a strand of RNA so that end of molecule has 3 bases (anticodon)
  • anticodon binds to complementary codon on mRNA
24
Q

What are the stages of protein synthesis?

A
  1. Initiation
  2. Elongation
  3. Termination
25
Q

What happens in each stage?

A

Initiation
- small ribosomal subunit binds to mRNA
- tRNA binds to start codon (AUG)
- large ribosomal subunit joins

Elongation
- ribosome moves along mRNA, reading each codon
- tRNA molecules brings corresponding amino acids, forming peptide bonds.
- ribosome moves to next codon, repeating the process

Termination
- translation stops at stop codon (UAA, UAG, UGA)
- ribosome releases polypeptide chain
- ribosomal subunits leave mRNA

26
Q

What can the genetic code be described as and why?

A
  • triplet code - each three bases (codon) codes for an amino acid
  • non-overlapping code - each triplet is read in sequence, separate from surrounding codons
  • degenerate code - many amino acids can be coded for my multiple codon
  • universal code - the same codons code for the same amino acids in almost all living organisms
27
Q

What is ATP made from?

A
  • 3 phosphate groups
  • ribose pentose sugar
  • adenine nitrogenous base
28
Q

Why is ATP not good for a long term store of energy?

A

The phosphate bonds are not stable

29
Q

How is energy released from ATP

A

ATP loses a phosphate group by hydrolysis, releasing energy and turning into ADP

30
Q
A

OCR Biology A Level (20 decks)

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