Nucleotides and Nucleic Acids Flashcards
Draw the structure of a nucleotide.
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Name the pentose sugars in DNA & RNA.
DNA: deoxyribose RNA: ribose
Describe how polynucleotide strands are formed and broken down.
Condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone). Hydrolysis reactions use a molecule of water to break these bonds.
Enzymes catalyse these reactions.
Describe the structure of DNA.
Molecule twists to form double helix of 2 deoxyribose polynucleotide strands (so there are 2 sugar-phosphate backbones).
H-bonds form between complementary base pairs (AT & GC) on strands that run antiparallel.
Name the purine bases and describe their structure.
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Name the pyrimidine bases and describe their structure.
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Name the complementary base pairs in DNA and RNA.
DNA: 2 H-bonds between adenine (A) + thymine (T)
RNA: 2 H-bonds between adenine (A) + uracil (U)
Both have 3 H-bonds between guanine (G) + cytosine (C)
Why is DNA replication described as semiconservative?
Strands from original DNA molecule act as templates.
New DNA molecule contains 1 old strand & 1 new strand (specific base pairing enables genetic material to be conserved accurately).
Explain the role of DNA helicase in semiconservative replication.
Breaks H-bonds between base pairs to form 2 single strands, each of which can act as a template.
How is a new strand formed during semiconservative replication?
- Free nucleotides from nuclear sap attach to exposed bases by complementary base pairing.
- DNA polymerase joins adjacent nucleotides on
new strand in a 5’ → 3’ direction via condensation
reactions to form phosphodiester bonds. - H-bonds reform.
Identify features of the genetic code.
● Non-overlapping: each triplet is only read once.
● Degenerate: more than one triplet codes for the
same amino acid (64 possible triplets for 20
amino acids).
● Universal: same bases and sequences used by
all species.
How does a gene determine the sequence of amino acids in a protein?
Consists of base triplets that code for a specific amino acids.
Describe how DNA can be purified by precipitation.
Add ethanol & a salt to aqueous solution. Nucleic acids precipitate out of solution.
Centrifuge to obtain pellet of nucleic acid. Wash pellet with ethanol & centrifuge again.
What does transcription produce and where does it occur?
produces mRNA occurs in nucleus
Outline the process of transcription.
- RNA polymerase binds to promoter region on a gene.
- Section of DNA uncoils into 2 strands with exposed
bases. Antisense strand acts as template. - Free nucleotides are attracted to their complementary
bases. - RNA polymerase joins adjacent nucleotides to form
phosphodiester bonds.
What happens after a strand of mRNA is transcribed?
● RNA polymerase detaches at terminator region.
● H-bonds reform & DNA rewinds.
● splicing removes introns from pre-mRNA in
eukaryotic cells.
● mRNA moves out of nucleus via nuclear pore &
attaches to ribosome.
What does translation produce and where does it occur?
Produces proteins
Occurs in cytoplasm on ribosomes
(which are made of protein + rRNA)
Outline the process of translation.
- Ribosome moves along mRNA until ‘start’ codon.
- tRNA anticodon attaches to complementary bases on
mRNA. - Condensation reactions between amino acids on tRNA
form peptide bonds. Requires energy from ATP
hydrolysis. - Process continues to form polypeptide chain until ‘stop’
codon is reached.
Describe the structure of adenosine triphosphate (ATP) and adenosine diphosphate (ADP).
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What is a mutation?
An alteration to the DNA base sequence. Mutations often arise spontaneously during DNA replication.
