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a level biology > Biological Molecules - Nucleic Acids > Flashcards

Biological Molecules - Nucleic Acids Flashcards

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1
Q

Describe The Structure of a Nucleotide

A

Phosphate Group-Pentose Sugar-Nitrogenous Base

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2
Q

Name The Pentose Sugars in DNA & RNA

A 
DNA = Deoxyribose
RNA = Ribose
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3
Q

State The Role of DNA in Living Cells

A

Base Sequence of Genetic Code For Functional RNA & Amino Acid Sequence of Polypeptides

Genetic Information Determines Inherited Characteristics = Influences Structure & Function of Organisms

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4
Q

State The Role of RNA in Living Cells

A
  • mRNA = Complementary Sequence to 1 Gene from DNA with Introns (non-coding regions) spliced out. Codons can be Translated into Polypeptide by Ribosomes
  • rRNA = Component of Ribosomes + Proteins
  • tRNA = Supplies Complementary Amino Acid to mRNA Codons During Translation
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5
Q

How Do Polynucleotides Form?

A

Condensation Reactions Between Nucleotides Form Strong Phosphodiester Bonds between Each Sugar and Phosphate - Sugar-Phosphate Backbone

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6
Q

Describe The Structure of DNA

A
  • Double Helix = 2 Polynucleotide Strands
  • Hydrogen Bonds Between Each Complementary Purine and Pyrimidine Base Pairs On Both Strands
  • Adenine + Thymine = 2 Hydrogen Bonds
  • Cytosine + Guamine = 3 Hydrogen Bonds
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7
Q

Which Bases are Purine/Pyrimidine?

A

Purine:
- Adenine and Guamine (2-Ring Purine Bases)
Pyrimidine:
- Thymine, Cytosine and Uracil (1-Ring Pyrimidine Bases

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8
Q

Relate The Structure of DNA to its Functions?

A
  • Sugar-Phosphate Backbone + Many Hydrogen Bonds Provide Stability
  • Long Molecule = Storage of Lots of Information
  • Compact Helix For Storage in Nucleus
  • Base Sequence of Triplets Codes For Amino Acids
  • Double-Stranded For Semi-Conservative Replication
  • Complementary Base Pairing For Accurate Replication
  • Weak Hydrogen Bonds = Strands Can Separate For Replication
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9
Q

Describe The Structure of Messenger RNA (mRNA)

A
  • Long Ribose Polynucleotide (but Shorter than DNA)
  • Contains Uracil Instead of Thymine (Bonds To Adenine)
  • Single-Stranded and Linear (No Base Pairing)
  • Codon Sequence is Complementary to Exons of 1 Gene From 1 DNA Strand
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10
Q

Relate mRNA’s Structure to its Functions

A

Given in Same Order As Description on Previous Card:

  • Long Ribose Polynucleotide Breaks Down Quickly = No Excess Polypeptide Forms
  • Ribosome can Move Along Strand and tRNA can Bind to Exposed Bases
  • Can be Translated into a Specific Polypeptide by Ribosomes
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11
Q

Describe The Structure of Transfer RNA (tRNA)

A
  • Single Strand of About 80 Nucleotides
  • Folded into Clover Shape - Has Some Base Pairing
  • Anticodon on One End, Amino Acid Binding Site on The Other:
    a) Anticodon Binds to Complementary mRNA Codon
    b) Amino Acid Corresponds to Anticodon
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12
Q

Order DNA, mRNA and tRNA According to Increasing Length

A

tRNA - mRNA - DNA

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13
Q

Why did Scientists Initially Doubt that DNA Carried Genetic Code?

A

Chemically Simple Molecule with Few Components

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14
Q

Why is DNA Replication Described as ‘Semi-Conservative’?

A
  • Strands From Original DNA Molecule Act as a Template

- New DNA Molecule Contains 1 Old and 1 New DNA Strand

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15
Q

Outline The Process of Semi-Conservative DNA Replication

A
  1. DNA Helicase Breaks Down Hydrogen Bonds Between Base Pairs.
  2. Each Strand Acts as a Template
  3. Free Nucleotides from Nuclear Sap Attach to Exposed Bases by Complementary Base Pairing
  4. DNA Polymerase Catalyses Condensation Reactions that Join Adjacent Nucleotides on New Strand
  5. Hydrogen Bonds Reform
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16
Q

Describe The Meselson-Stahl Experiment and How Does it Relate to and Prove Semi-Conservative DNA Replication?

A
  1. Bacteria Were Grown in a Medium Containing Heavy Isotope ^15N for Many Generations
  2. Some Bacteria Were Moved to a Medium Containing Light Isotope ^14N. Samples Were Extracted After 1 & 2 Cycles of DNA Replication
  3. Centrifugation Forms a Pellet. Heavier DNA (bases with 15N) Settled Closer to Bottom of Tube.

Demonstrates that Each Strand in a DNA Molecule Serves as a Template as Replication Occurs.

a level biology (7 decks)

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