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Questions and Answers
What are the three parts that make up a nucleotide?
What are the three parts that make up a nucleotide?
- Deoxyribose sugar, phosphate group, amino acid
- Ribose sugar, phosphate group, nitrogen base
- Deoxyribose sugar, phosphate group, nitrogen base (correct)
- Deoxyribose sugar, phospholipid, nitrogen base
Which statement about complementary base pairing is true?
Which statement about complementary base pairing is true?
- G pairs with U which is found in DNA.
- A pairs with T through two hydrogen bonds. (correct)
- C pairs with T through three hydrogen bonds.
- A pairs with G through two hydrogen bonds.
How are the two strands of DNA organized?
How are the two strands of DNA organized?
- They twist in the same direction throughout the entire molecule.
- They run parallel to each other.
- They are circular and do not have ends.
- They run antiparallel, with a 5' end on one strand opposite a 3' end. (correct)
Which of the following nucleotides is not found in DNA?
Which of the following nucleotides is not found in DNA?
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What aspect characterizes the structure of prokaryotic DNA?
What aspect characterizes the structure of prokaryotic DNA?
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What enzyme is responsible for controlling DNA supercoiling?
What enzyme is responsible for controlling DNA supercoiling?
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Which statement regarding the majority of DNA in an organism's genome is true?
Which statement regarding the majority of DNA in an organism's genome is true?
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What does the term 'genome' refer to?
What does the term 'genome' refer to?
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Study Notes
DNA Structure & Organization
- Deoxyribonucleic Acid (DNA) is made of repeating subunits called nucleotides.
- Nucleotides are composed of three parts:
- Deoxyribose sugar (5 C)
- Phosphate group
- Nitrogen base
- Nucleotide structure:
- Phosphate group is attached to carbon 5 (5’) of the deoxyribose sugar.
- Nitrogen base is attached to carbon 1 (1’) of the deoxyribose sugar.
- The next nucleotide attaches to carbon 3 (3’) of the deoxyribose sugar.
- Nitrogen bases:
- Two types of nitrogen bases:
- Pyrimidines: Single rings
- Uracil (U, present only in RNA)
- Thymine (T, present only in DNA)
- Cytosine (C)
- Purines: Two rings
- Adenine (A)
- Guanine (G)
- Pyrimidines: Single rings
- Two types of nitrogen bases:
- Complementary base pairing:
- Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.
- Adenine (A) pairs with Thymine (T) via two hydrogen bonds.
- Both pairs have the same diameter.
- Double helix:
- DNA is composed of two strands.
- The phosphate and sugar molecules form the backbone on the outside.
- Strands run antiparallel, meaning the 5' end of one strand is across from the 3' end of the other strand.
- The direction of the helix is clockwise.
- One turn of the helix contains 10 nucleotides.
- The nucleotides are spaced 0.34 nm apart.
- Complementary base pairing:
- The two strands of DNA are complementary due to the hydrogen bonds formed between the nitrogenous bases.
- Each strand has a 5′ end and a 3′ end.
- Organization of DNA
- Genome: the total genetic material of an organism.
- Gene: a functional unit of DNA.
- Most of the DNA in an organism's genome is non-coding and does not contain genes.
Prokaryotes
- Prokaryotes have a circular, double-stranded DNA molecule.
- DNA is not contained within a nucleus and instead is packed in a region called the nucleoid.
- DNA is tightly packed by coiling, compacting, and supercoiling.
DNA supercoiling
- Supercoiling is the formation of additional coils in the DNA structure due to twisting forces.
- Supercoiling is controlled by the enzymes topoisomerase I and topoisomerase II.
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