Biochemistry DNA

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How do nucleotides bind together to form a single strand of nucleic acids?
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-monophosphate group on the 5′ C of one nucleotide binds to the hydroxyl of the 3′ C of another nucleotide –> this is a phophoester -this creates a phosphodiester linkage
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phosphodiester linkage
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Nucleic acids consist of
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Nucleic acids consist of chains of nucleotides with a sugar-phosphate backbone. They do not contain amino acids, carbohydrate or lipid.
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At human physiologic pH, the phosphate is deprotonated, therefore
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nucleic acids are very negatively charged.
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Two major types of Nucleic acids :
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Ribonucleic Acid (RNA) Deoxyribonucleic Acid (DNA)
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RNA is a nucleic acid similar to DNA, except:
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1. nitrogenous base – adenine, guanine, cytosine, uracil – RNA never has thymine, always uracil – (uracil is not methylated at the #5 carbon, thymine is) 2. sugar – RNA never has deoxyribose, always ribose 3. RNA is single-stranded not double-stranded and doesn’t form helices
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The monomeric units of DNA are ____
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nucleotides.
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DNA is a polymer of ___________
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nucleotides (polynucleotide).
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DNA molecules are bonded to a nucleoprotein called histone. Together they are called a chromosome. ( Tor F)
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True
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Chargaff’s rule DNA has:
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DNA has: the same number of purines as pyrimidines the same number of A as T the same number of G as C
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Rosalind Franklin and Maurice Wilkins used x-ray crystallography of DNA that helped determine the____________
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the double helix structure of DNA
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One strand of the DNA double helix is always the complement of the other strand. The two are _______
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antiparallel.
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How do two strands of nucleotides bind together to form a double strand of nucleic acids?
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A binds only to T ->forms 2 hydrogen bonds G binds only to C -> forms 3 hydrogen bonds
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the largest human DNA molecule (#1) is about ________
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2.4 x 10 8 bp
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DNA stretched out =
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8 centimeters!
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all 46 DNA molecules stretched out, end to end would equal
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2 meters! therefore, in order to fit in the nucleus, they must be markedly condensed in size
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Any part of the DNA molecule that is not being actively transcribed, is coiled up. (T or F)
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True
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A protein called histone assists with the _______
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coiling.
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Histone’s lys and arg side chains (residues) combine with the negatively charged backbone of DNA. (T or F)
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True
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DNA “wraps” around it 2-3 times (about 200bp) forming a ____ ___
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core particle.
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There are many thousands of nucleosomes per ________
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chromosome.
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This shortens the DNA molecule about _____
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ten-fold.
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DNA bonded to histones is called ____
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chromatin (chromosome if fully condensed).
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nucleosomes coil into a _______
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30 nm chromatin fiber (this further reduces length by four-fold)
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Overall, there is an 8000 times reduction in the length of the DNA molecule!! T or F
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True 30 nm fibers are bound to another nucleoprotein (scaffold) and form up to several thousand loops surrounding it. This gives an additional 200-fold decrease in the length of the DNA molecule 10 x 4 x 200 = 8000
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If the chromatin is available for gene transcription, it is called _______ If not ______
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euchromatin. If not, it is more condensed and called heterochromatin.
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Euchromatin
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“active” DNA less condensed more accessible to transcription the Lys residues of the histones of this part of DNA are often acetylated (adds a COCH3 group) -> so the DNA can detach at that point
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Heterochromatin
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Heterochromatin “inactive” DNA more condensed and the genes are not being transcribed this DNA is often methylated (most commonly 5-methylcytosine)
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Like proteins, DNA can be denatured by:
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temperature pH enzymes toxic molecules electromagnetic waves with high energy UV, x-ray, gamma rays

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