Nucleic acids

Question 1

Nucleotides

Answer 1

they are the monomer from which all nucleic acids are formed

the phosphate is always the same in all nucleotides

they are polymerised by polymerase enzymes into single, polynucleotide strands

each nucleotide is joined to the next by a phosphodiester bond

Question 2

how are phosphodiester bonds made and destroyed?

Answer 2

they are made by condensation reactions and destroyed by hydrolysis

Question 3

pentose sugar

Answer 3

can either be deoxyribose (in DNA) or ribose (in RNA)

Question 4

nitrogenous bases

Answer 4

there are 5 and can be classified as either a purine (double ring base) or a pyrimidine (single ring base)

Question 5

Purine

Answer 5

A - Adenine, G - Guanine, both found in DNA and RNA

Question 6

Pyramidine

Answer 6

T - Thymine - DNA only, C - Cytosine - DNA and RNA, U - Uracil - RNA only

Question 7

ATP and ADP

Answer 7

Adenosine Triphosphate, universal energy currency for metabolic reactions, ATP yields energy when a phosphate group is removed and will produce ADP - Adenosine Diphosphate and an inorganic phosphate group, this energy can then be used to carry out work in the cell, as part of process of respiration, ADP and inorganic phosphate are joined together in order to regenerate supplies of ATP

Question 8

metabolic reactions

Answer 8

the reactions that occur in cells and organisms as an essential part of life

Question 9

DNA

Answer 9

has a sugar-phosphate backbone that are joined by phosphodiester bonds which are very strong, joining the bases of the two DNA strands together are hydrogen bonds which are much weaker, two hydrogen bonds form between A and T, three hydrogen bonds form between G and C, that is known as complimentary base pairing, the two polynucleotide strands run anti-parallel to one another and are twisted to form a double helix

Question 10

Purification of DNA by precipitation

Answer 10

1. break up the cells
2. add a detergent and a slat solution to the sample
3. place sample in water bath, the detergent will breakdown the cell membranes and the salt binds to DNA causing it to clump together
4. place in an ice bath to cool mixture
5. filter the sample, add protease enzymes ( breaks down the histone proteins associated with the DNA) 6. slowly trickle ice cold ethanol down the side of the tube containing the sample to form a layer on top of the DNA mixture
6. after a few minutes, DNA will form a visible white ppt at the ethanol-sample interface which can be removed

Question 11

conservative hypothesis

Answer 11

the complete parent DNA molecule acts as a template for the new daughter molecule, which is assembled from new nucleotides, the parent molecule remains unchanged

Question 12

DNA replication

Answer 12

1. DNA helicase causes the two strands of DNA to separate
2. DNA helicase completes the separation of the strands whilst free nucleotides that have been activated are attracted to their complimentary bases
3. once the activated nucleotides are lined up, they are joined together by DNA polymerase whilst the remaining unpaired bases continue to attract their complimentary nucleotides
4. finally all the nucleotides are joined together to form a complete polynucleotide chain using DNA polymerase, two identical molecules of DNA are formed, each new molecule of DNA is composed of one original strand and one newly formed strand (semi-conservative replication)

Question 13

Genetic code

Answer 13

refers to the sequence of bases which codes for the order of amino acids in a protein/polypeptide, triplet code - each amino acid is coded for by a sequence of 3 bases, non overlapping - each base is part of only one triplet code, universal - a particular triplet code will always code for the same amino acid no matter what organism, degenerate - many amino acids have more than one triplet coding for them

Question 14

Codon

Answer 14

each coding triplet in mRNA is called a codon, a start codon is usually a codon at the start of a sequence, there are also stop codons, these stop codons do not code for an amino acid and they signal the end of synthesis of a polypeptide

Question 15

Transcription

Answer 15

the template strand is copied via complimentary base pairing of RNA nucleotides with the DNA nucleotides of DNA to form a much shorter molecule called pre-mRNA, this messenger molecule can fit through nuclear pores to enter either the cytoplasm or the RER to journey to ribosomes, during this journey the pre-mRNA is sliced to remove non-coding sections, once spliced the molecule is known as mRNA

Question 16

Translation

Answer 16

one end of tRNA molecule attaches to a specific amino acid and other end has a specific sequence of three bases called an anti-codon which can bind to a complementary codon on the mRNA via hydrogen bonding, mRNA formed in transcription joins to a ribosome and the sequence of baeses in the codons are ‘read’, tRNA molecules with anti-codons complementary to the mRNA codons will bind via complementary base pairig (hydrogen bonds), tRNA molecules will be carrying a specific amino acid and the sequence of bases on the mRNA codons is translated into the correct sequence of amino acids, a peptide bond will form between the two amino acids in the mRNA-ribosome complex, and then the first tRNA molecule is released, the ribosome then moves along one codon and the next tRNA molecule with a complementary anti-codon will bind, the process will continue until a stop codon is reached and synthesis of the polypeptide finishes