Biology DNA Structure

Structure and function of DNA

  • Created by: Tony Rule
  • Created on: 25-02-12 17:06

What is DNA

Deoxyribonuucleic acid is a nucleic acid. It is a polymer of sub--units called nucleotides. It consists of 2 polynucleotide strands held together by hydrogen bonds to form an alpha double helix.

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What is a gene?

A gene is a section of DNA that contains coded information as a specific sequence of bases.

Genes code for polypeptides that determine the nature and development of an organism.

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What does a nucleotide consist of?

Each nucleotide consists of 3 molecules joined by a condensation reaction:

  • A pentose sugar
  • a phosphoric acid molecule
  • an organice base
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Which bases are complimentary to eachother and whi

A+T - Complimentary + Pyrimidine

C+G - Complimentary + Purine (double ringed bases)

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Give the structures and their functions of DNA

  • Sugar-phosphate backbone - gives strength
  • Coiling of DNA - gives compact shape
  • Double helix - protects sequence of bases + keeps molecule more stable
  • Large molecule - Allows a large amount of information to be stored
  • Many hydrogen bonds - give stability + prevents code being interrupted + allows chain to easily unzip for replication
  • Sequence of bases - codes for synthesis of specific proteins
  • Complimentary Base Pairing - enables information to be replicated accurately
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What is an Allele?

An allele is a gene existing in a different form

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What is a sequence of 3 bases known as?

A codon - these code for specific amino acids

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  • differ in their base sequence + code for different sequence of amino acids hence different polypeptides are produced
  • This change in polypeptides makes the protein non-functional as there is a change in the tertiary structure of the protein
  • This is because a change in the base sequence affects the hydrogen, ionics and (if present) disulfide bonds
  • If the protein coded for is an enzyme, the shape of the active site may be altered and therefore the enzyme is non-functional as the substrate cannot attach and an enzyme-substrate complex cannot be formed
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What is the haploid number? What is the diploid nu

Haploid = (n) 23

Diploid = (2n) 46

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What 3 stages does the cell cycle consist of? expl

Interphase - represents the non-dividing cell when cell growth occurs

Nuclear division - the nucleus divides into 2 (mitosis) or 4 (meiosis)

Cell division - The cell divides into 2 (mitosis) or 4 (meiosis)

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Describewhat happens during Interphase

During late interphase the cell prepares for division in the following ways:

  • There is an increase in protein synthesis inside the cell
  • The DNA content replicates via DNA replication
  • Cell organelles are replicated
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Descrine what happens during Prophase

Chromosomes form and become visable. Each chromosome consists of 2 identical chromatids.

Each chromosome shortens and thickens

Centrioles move to opposite poles of the cell and nuclioli and nuclear membrane break down

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Describe what happens during Metaphase

Centrioles form a spindle across the cell - the spindle consists of protein microtubules

Each chromosome moves to the equator of the spindle and attaches to it via its centromere

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A + T are both not pyrimidine and C + G are both not purine.

As purine and a pyrimidine bond together.

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