2.3 Nucleic Acids Flashcards
What are nucleotides?
monomer from which nucleic acids are made
Give examples of phosphorylated nucleotides?
ADP and ATP.
What is a nucleotide made from?
- phosphate group
- five carbon sugar
- nitrogenous base
What’s the covalent bond between the sugar residue and the phosphate group also known as?
Phosphodiester bond.
What type of reaction joins the sugar residue, base and phosphate group?
Condensation reaction.
Which bases are purine?
Adenine and guanine.
Which bases are pyramidine?
Thymine or cytosine.
Which bases are one ring bases?
Thymine and cytosine.
How are the two antiparallel DNA strands joined together?
Hydrogen bonds.
How made hydrogen bonds does an A-T pairing have?
Two hydrogen bonds.
How many hydrogen bonds does a C-G pairing have?
Three.
What is each DNA molecule wound around to make a chromosome?
Histone protein.
In semi-conservative replication, which enzyme catalyses the double helix untwist?
Gyrase enzyme.
In DNA replication, which enzyme catalyses the unzipping of the molecule?
DNA helicase breaks hydrogen bonds.
In DNA replication, which enzyme catalyses the addition of new nucleotide bases?
DNA polymerase.
Which direction does DNA polymerase add nucleotide bases?
5’ to 3’ direction.
What is semi-conservative replication?
How DNA replicates, resulting in two new molecules, each of which contains one old strand and one new strand.
What enzyme joins the lagging strand fragments in DNA replication?
Ligase.
How do the loops of DNA in prokaryotes replicate?
A bubble sprouts from the loop and this unwinds and unzips, and the complementary nucleotides join to the exposed nucleotides.
What is the replication fork?
The point at which the two strands are separated.
How is RNA structurally different from DNA?
- the nitrogenous base, uracil, which is a pyramidine, replaces the pyramidine base thymine
- RNA is usually a single stranded polynucleotide chain
- RNA polynucleotide chain is shorter
- there are three forms of RNA
Why is the genetic code described as degenerate?
Because, for all amino acids, except methionine and trypotophan, there is more than one bass triplet.
What is a codon?
A triplet of bases in a length of mRNA.
What is an anticodon?
A triplet of bases on a tRNA molecule.
What is used to show the distribution of DNA and RNA with cells? How?
Methyl green-pyronin.
DNA stained blue-green in nuclei
RNA stained red in cytoplasm.
Define double helix.
shape of DNA due to coiling of the two sugar phosphate backbone strands into a right handed spiral configuration
Define nucleotide
Molecule consisting of a five carbon sugar, phosphate group and a nitrogenous base
Define DNA polymerase
Enzyme that catalyses formation of DNA from activated deoxyribose nucleotides, using a single stranded DNA as a template
Define helicase
Enzyme that catalyses the breaking of hydrogen bonds between the nitrogenous pairs of bases in a DNA molecule
Define semi conservative replication
How DNA replicates, resulting in two new molecules, each of which contains one old strand and one new strand. One old strand is conserved in each new molecule
Define gene
Length of DNA that codes for a polypeptide or for a length of RNA that is involved in regulating gene expression
Define polypeptide
A polymer made of many amino acid units joined together by peptide bonds
Define protein
A large polypeptide of 100 or more amino acids
Define transcription
The process of making messenger RNA from a DNA template
Define translation
Formation of a protein, at ribosomes, by assembling amino acids into a particular sequence according to the coded instructions carried from DNA to the ribosome by mRNA
What are ADP and ATP?
Phosphorylated nucleotides
What elements do nucleotides contain?
C H O N P
Whats the sugar in DNA called?
Deoxyribose
How many carbon-nitrogen rings do purines have?
Two
How many carbon-nitrogen rings do pyramidines have?
One
What is the base in ADP and ATP?
adenine
Where is energy stored in a molecule of ATP?
In the phosphate bond
What does a phosphodiester bond consist of?
phosphate group and two ester bonds
Why is the double helix twisted?
Because the two strands are antiparallel
How can you purify DNA using a precipitation reaction?
- Blend cells to break them up
- Make solution of detergent (eg washing up liquid), salt and distilled water
- add cells to beaker with detergent solution
- incubate beaker for 15 mins at 60 degrees in waterbath
- cool in ice bath
- filter + transfer to clean boiling tube
- add protease enyzmes and RNAase
- dribble cold ethanol down side so it forms a layer
- leave for a few mins, DNA will form a white precipitate which you can remove using a glass rod
What does the detergent in the purifying DNA experiment do?
Breaks down cell membranes
What does salt in the purifying DNA experiment do?
Binds to DNA and causes it to clump together
Why do you incubate the DNA purification solution?
To stop the enzymes in the cells from working properly and breaking down DNA
Why is it important that DNA replication is very accurate?
To make sure genetic information is conserved
Describe the nature of the genetic code?
Universal
Degenerate
Non-overlapping
Why is the genetic code described as universal?
Because in almost all living organisms the same triplet of bases codes for the same amino acid
Why must DNA be copied into mRNA?
Because it is too large to leave the nucleus
Describe mRNA
- made in nucleus
- carries genetic info from nucleus to cytoplasm
Describe tRNA
- found in cytoplasm
- has an amino acid binding site at one end and a sequence of three bases at the other end
- carries amino acids
Where is the anticodon?
on tRNA
Describe rRNA
- forms the two subunits of a ribosome
- helps to catalyse the formation of peptide bonds between the amino acids
Explain how the structure of DNA allows replication
- double stranded
- each strand = template
- H bonds break easily
- complementary base pairing
- purine only binds with pyrimidine
Why is complementary base pairing important in DNA replication?
- DNA can be replicated without error
- reduces occurrence of mutation
- allows reformation of hydrogen bonds
Describe how DNA replicates
- semi conservative replication
- helix untwists
- hydrogen bonds break
- each strand acts as template
- free DNA nucleotides complementary base pairing
- hydrogen bonds reform
- sugar phosphate backbone forms
- DNA polymerase joins
- each has 1 old 1 new
Why is mRNA shorter than DNA?
only copies one gene/section
DNA has many genes
How can a protein be affected by changing the sequence of DNA nucleotides?
- different sequence of amino acids
- different protein
- different function
How many base pairs are there in one full turn of the DNA double helix?
10
What technique was used to determine the double helical structure of DNA?
X-ray crystallography
