Chapter 3 Flashcards
What are the 2 major biological functions of DNA?
- stores genetic information that is encoded in the sequence of subunits along its length
- transmits genetic information in other molecules and from one generation to the next
What does some of the information in DNA encode?
proteins that provide structure and do much of the work of the cell
What form is genetic information in DNA organized in?
genes
How do genes exist?
in different forms in different individuals, even with a single species
What is gene expression?
turning on of a gene
What is gene regulation?
the molecular process that control whether gene expression occurs at a given time, in a given cell, or at what level
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What are nucleotides composed of?
5-carbon sugar
base
phosphate group(s)
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What are the nucleotide components’ roles in DNA structure?
- 5-carbon sugar and phosphate groups form the backbone of the molecule, with each sugar being linked to the phosphate group of the neighbouring nucleotide
- bases sticking out from the sugar give each nucleotide its chemical identity
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What makes DNA a mild acid?
phosphate group attached to 5’ carbon has negative charges on two of its oxygen atoms because at cellular pH, the free hydroxyl groups attached to the phosphorous atom are ionized by the loss of a proton and therefore are negatively charged
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Where is each base located?
attached to 1’ carbon of the sugar and projects above the sugar ring
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What are nucleosides?
combination of sugar and a base
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What is a nucleotide?
a nucleoside with one or more phosphate groups
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What is a nucleotide with one, two, or three phosphate groups called?
nucleoside monophosphate, diphosphate, triphosphate
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What is nucleoside triphosphate?
- molecules that are used to form DNA and RNA
- carriers of chemical energy in the form of ATP and GTP
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What is a phosphodiester bond?
covalent bond that connects 3’ carbon of one nucleotide to 5’ carbon of the next nucleotide in line through the 5’ phosphate group
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Describe the phosphodiester bond.
in DNA, it is a relatively stable bond that can withstand stresses such as heat and substantial changes in pH that would break weaker bonds
- succession of phosphidester bonds traces the backbone of the DNA strand
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What gives DNA strand polarity?
phosphodiester linkages
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What does polarity in a DNA strand mean?
one end differs from the other - 5’ end (phosphate) and 3’ end (hydroxyl)
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Describe the Watson-Crick structure of DNA.
- space-filling model in which each atom is represented as a colour-coded sphere
- two DNA strands, each wrapped around the other in the form of a helix coiling to the right, with the sugar-phosphate backbones winding around the outside of the molecule and bases pointing inward
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How many base pairs are there per DNA turn?
10 base pairs per complete turn
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What are major and minor grooves?
outside contours of the twisted strands form an uneven pair of grooves
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Why are major and minor grooves important?
because proteins that interact with DNA often recognize a particular sequence of bases by making contact with the bases by the major or minor groove or both
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Describe the ribbon model of DNA.
- sugar-phosphate backbones wind around the outside with the bases paired between the strands
- closely resembles a spiral staircase, with the backbones forming the bannisters and the base pairs the steps
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What is Chargaff’s rule?
- AT and GC base pairing maintains the structure of the double helix
- pairing one purine and on pyrimidine preserves the distance between the backbones along the length of the entire molecule
- pairing two purines would cause the backbone to bulge and pairing two pyrimidines would cause them to narrow, putting excessive strain on the covalent bonds in the sugar-phosphate backbone