2.1.3 - Nucleotides and Nucleic Acids Flashcards
What is a nucleic acid?
a polymer of nucleotides
What are nucleotides?
the monomers that makes up nucleic acids
What is a nucleotide made up of? (its basic structure)
a phosphate group
a pentose sugar
a nitrogenous base
Which pentose sugar is found in DNA?
deoxyribose
Which pentose sugar is found in RNA?
ribose
What nitrogenous bases are found in DNA?
adenine (A)
thymine (T)
guanine (G)
cytosine (C)
What nitrogenous bases are found in RNA?
adenine (A)
uracil (U)
guanine (G)
cytosine (C)
What are pyrimidines?
smaller bases which contain a single carbon ring structure
-cytosine, thymine(/uracil)
What are purines?
larger bases which contain double carbon ring structure
-adenine, guanine
What covalent bond is formed between nucleotides?
phosphodiester bond
What happens when two nucleotides join?
-condensation reaction
-phosphodiester bond formed
-phosphate group (C5) of one nucleotide joins with the hydroxyl group (C3) of the pentose of another nucleotide
What are the base pairing rules?
1) A always pairs with T/U
G always pairs with C
2) 2 hydrogen bonds form between A and T/U
3 hydrogen bonds form between C and G
3) Pyrimadines (C, T, U) always pair with purines (A, G)
What is the structure of DNA?
-2 strands of polynucleotides coiled into a double helix
-held together by hydrogen bonds between bases
-strands run in opposite directions, making them antiparallel (3->5 and 5->3)
What are the differences between DNA and RNA?
-pentose sugars -deoxyribose in DNA and ribose in RNA
-RNA has a uracil base where DNA has a thymine base
-DNA is double stranded but RNA is single stranded
What are the similarities between DNA and RNA?
-both have nucleotides as their monomer
-both have A, C and G bases
-both have phosphodiester bonds
Why is DNA replication semi-conservative?
the replicated DNA contains one newly formed strand and one original strand (which acts as a template)
What happens in DNA replication?
-DNA double helix unwinds (by DNA gyrase)
-the H-bonds between bases are broken (by DNA helicase)
-free activated DNA nucleotides complementary base pair to exposed bases
-DNA polymerase forms phosphodiester bonds between nucleotides
What does the enzyme DNA gyrase do?
unwinds the DNA double helix
What does the enzyme DNA helicase do?
breaks hydrogen bonds between bases
What does the enzyme DNA polymerase do?
catalyses formation of phosphodiester bonds between nucleotides (forming sugar phosphate backbone)
What is the leading strand in DNA replication?
the strand that is unzipped (by DNA polymerase) from the 3’ end -so is continuously replicated (undergoes continuous replication)
What is the lagging strand in DNA replication?
the strand that is unzipped (by DNA polymerase) from the 5’ end (meaning DNA polymerase has to wait for a section to be unzipped and then work back along the strand) so undergoes discontinuous replcation
-in the lagging strand, the DNA is produced in sections (okazoki fragments) which DNA ligase joins together
What does the enzyme DNA ligase do?
joins the Okazoki fragments in discontinuous replication together
What is genetic code?
the sequence of bases in DNA, which acts as an instruction for the order of amino acids (ie the primary structure of a protein) when proteins are being produced
What is a codon?
a three base sequence of DNA/RNA
-each codon codes for an amino acid
What are the two stages of protein synthesis?
transcription (base sequences are copied and transported to ribosomes)
translation (complementary code is decoded by tRNA into primary structure of protein)
What is the sense strand in protein synthesis?
DNA strand containing correct code to be synthesised
What is the antisense strand in protein synthesis?
the complementary copy of the sense strand
(doesn’t code for protein but acts as template to produce DNA like the sense strand)
What happens in transcription?
-DNA double helix is unwound and unzipped (H-bonds are broken)
-antisense strand acts as template strand
-free RNA nucleotides pair with complementary pairs on exposed antisense strand
-DNA polymerase forms phosphodiester bonds between RNA nucleotides
-mRNA leaves nucleus through pore in nuclear envelope (to travel to ribosome)
-double helix reforms
What happens in translation?
-mRNA binds to ribosome at its start codon
-tRNA’s anticodon binds to a codon on mRNA (max 2 can at one time)
-peptide bond forms between amino acids on tRNA molecules (this is catalysed by peptidyl transferase)
-ribosome moves along mRNA and the tRNA from the first codon is released, leaving its amino acid attached to the next amino acid
-process continues (so a polypeptide chain forms) until the ribosome reaches the stop codon and the polypeptide chain is released
What does ATP supply energy for?
-synthesis
-transport
-movement
What is ATP made up of? (its structure)
-ribose sugar
-adenine (nitrogenous base)
-three phosphate groups
Why is ATP a good energy source?
-small
-water soluble
-releases energy in small quantities
-easily regenerated
Describe the procedure for extracting DNA
-grind sample
-mix with detergent
-add salt
-place in hot water bath
-add protease
-add layer of ethanol
Why do you grind the sample in DNA extraction?
to break cell walls so that detergent can get inside cells
Why do you mix with detergent in DNA extraction?
breaks cell membranes so that cell contents are released into the detergent
Why do you add salt in DNA extraction?
breaks H-bonds between DNA bases and water
Why do you place in hot water bath in DNA extraction?
stops enzymes from breaking DNA down
Why do you add protease in DNA extraction?
breaks histamines in DNA down
Why do you add a layer of ethanol in DNA extraction?
DNA doesn’t dissolve in alcohol so will precipitate
