DNA Need to know – molecular components, role of each. Revisit y12.
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Transcript of DNA Need to know – molecular components, role of each. Revisit y12.
![Page 1: DNA Need to know – molecular components, role of each. Revisit y12.](https://reader035.fdocuments.net/reader035/viewer/2022072015/56649ec85503460f94bd4ecd/html5/thumbnails/1.jpg)
DNA
• Need to know – molecular components, role of each.
• Revisit y12
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Prokaryotes
• ‘simple’ cells, lack many organelles, DNA not bound in a membrane.
• Relatively small cells
• Cell wall of peptidoglycan
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Eukaryotes
• Relatively large
• Membrane bound DNA
• Many organelles
• Fungi, protists, animals and plants
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DNA• DNA is often called
the blueprint of life.• In simple terms,
DNA contains the instructions for making proteins within the cell.
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Why do we study DNA?
We study DNA for many reasons, e.g.,
• its central importance to all life on Earth,
• medical benefits such as cures for diseases,
• better food crops.
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The Shape of the Molecule
• DNA is a very long polymer.
• The basic shape is like a twisted ladder or zipper.
• This is called a double helix.
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One Strand of DNA• The backbone of
the molecule is alternating phosphate and deoxyribose, a sugar, parts.
• The teeth are nitrogenous bases.
phosphate
deoxyribose
bases
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One Strand of DNA
• One strand of DNA is a polymer of nucleotides.
• One strand of DNA has many millions of nucleotides.
nucleotide
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Chromosomes
• The DNA is joined together into structures called chromosomes.
• The pinch in the middle is the centromere
• Stripes are the banding pattern
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Genes• Each chromosome is divided up into areas called genes.
• Each gene codes for a single trait or characterisitic.
• Eg eye colour, height
• You get one copy of each gene from each parent.
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Fig 2.4 The structure of a highly condensed, replicated chromosome.© 2003 John Wiley and Sons Publishers
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• Chromosomes are paired together.
• You get one from each pair from each parent.
• The ‘map’ of the pairs is a karotype
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• Diploid is the normal number of chromosomes in an autosome cell – e.g. 46 in humans.
• Haploid is the normal number in a sex cell e.g. 23 in humans
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RECAP
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Structure
• Sugar is deoxyribose, 5 carbons.• Four bases: two purines (adenine and guanine)
and two pyrimidines (cytosine and thymine).• Shape double helix held by weak hydrogen
bonds• The nucleotide strands run in opposite
directions – link is via the sugar so one runs 3’ to 5’ and vice versa. D
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Function
• Carries genetic code for proper functioning of organisim
• Has ability to replicate itsself
• Very long and has genes positioned in set places called loci/locus.
• Genes code for a polypeptide chain One or more polypeptide chains make a
protein D
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Packaging
• Prokaryote=ring
• Eukaryote needs packaging as so long.
• Chromatin when unwound, chromosome when wound and looped.
• Loop around histones which form the chromatid.