a1.2 nucleic acids

Question 1

what are the primary functions of nucleic acids?

Answer 1

1. to pass information between generations
2. to code for protein production

Question 2

what is DNA?

Answer 2

deoxyribonucleic acid:
-> found in nucleus/nucleoid region
-> passes heredity information between generations of cells
-> codes for making RNA during transcription

Question 3

what is RNA?

Answer 3

ribonucleic acid:
-> found in cytoplasm
-> codes for making proteins during translation
-> mRNA, rRNA, and tRNA are the three main types of RNA involved in protein synthesis

Question 4

what is a nucleic acid?

Answer 4

nucleic acids are chains of nucleotides combined in condensation reactions. the nucleotide is considered the ‘monomer’ and the nucleic acid the ‘polymer’

Question 5

what makes up a nucleotide?

Answer 5

1. a purine or pyrimidine nitrogenous base (A, T, G, C, U)
2. a five carbon pentose sugar
3. a negatively charged phosphate group

Question 6

what is a sugar phosphate backbone?

Answer 6

the covalently bonded phosphates and sugars create a strong backbone for the nucleic acid. this strength maintains the nucleotides in their specific sequence

Question 7

how is the sugar phosphate backbone formed?

Answer 7

condensation reactions join the nucleotides together with covalent bonds to form the ‘sugar phosphate backbone’ - a polynucleotide strand of DNA. the 5’ phosphate group on one nucleotide forms a new covalent bond with the 3’ carbon on the pentose of the next nucleotide, meaning the backbone is built from 3’ to 5’

Question 8

what is the difference between a purine and a pyrimidine base?

Answer 8

based on the number of chemical rings in their structure, the nitrogenous bases are grouped as either purine (double ring structure) or pyrimidine (single ring structure)

Question 9

what is a gene?

Answer 9

a gene is a specific sequence of nitrogenous bases in DNA nucleotides that codes for the making of a protein

Question 10

how does the sequence of bases form a code?

Answer 10

3 consecutive bases forms a triplet code which codes for a specific amino acid

Question 11

what is the structure of a DNA molecule?

Answer 11

in DNA, two backbones will hydrogen bond together to create a double helix. the two different strands of the DNA double helix run in opposite directions. at each end of the double helix, one strand is 5’ and the other 3’.
adenine pairs with thymine with two hydrogen bonds whilst guanine pairs with cytosine with three hydrogen bonds

Question 12

what does semi-conservative DNA replication mean?

Answer 12

DNA replication takes place during interphase of the cell cycle. the DNA helix is unwound and unzipped by the enzyme helicase which breaks the weak hydrogen bonds between the base pairs. the exposed, unpaired bases form a template. free nucleotides are specifically base paired to the exposed bases by the enzyme DNA polymerase - this requires ATP as a source of energy. two identical DNA molecules are produced: since each of the new DNA molecules retains half an old one, DNA replication called semi conservative

Question 13

what’s the role of complementary base pairing in transcription?

Answer 13

transcription is the synthesis of RNA using a DNA template. the enzyme RNA polymerase builds an RNA strand by reading the DNA template and adding the complementary RNA nucleotide. transcriptions results in the RNA strand having the complementary sequence of bases as the DNA, thereby maintaining the information stored in the sequence of nucleotides of the code

Question 14

what’s the role of complementary base pairing in translation?

Answer 14

translation is the synthesis of a polypeptide from mRNA. the ribosome builds a polypeptide by reading the mRNA template and binding the coded amino acid to the polypeptide chain. the amino acids are brought to the ribosome by tRNA. the tRNA forms a temporary bond to the mRNA using complementary base pairing

Question 15

where is there a limitless diversity of DNA base sequences?

Answer 15

nucleotides joined together in any sequence means a huge range of possible base sequences. for a chain of 2 nucleotides, the number of possible sequences is 4^2 (=16). genes can be several thousand nucleotides long meaning there is a huge number of possible combinations

Question 16

what does universal mean in relation to genetic code?

Answer 16

the genetic code is universal, meaning that all living organisms use the same genetic code - even viruses used the same code

Question 17

in what direction is DNA replicated?

Answer 17

the enzyme that builds DNA during replication, DNA polymerase, can only add nucleotides to the 3’ end of a growing polymer of DNA. the 5’ phosphate is added to the 3’ deoxyribose end of the growing DNA strand - in this way, DNA replication is 5’ to 3’

Question 18

in what direction is transcription?

Answer 18

transcription is the synthesis of RNA using a DNA template. the enzymes of transcription, RNA polymerase, can only add nucleotides to the 3’ end of a growing polymer of RNA nucleotides. the 5’ phosphate end is added to the 3’ ribose end of the growing RNA strand. in this way, transcription is 5’ to 3’

Question 19

in what direction is translation?

Answer 19

translation is the synthesis of polypeptides from the mRNA code. during initiation of translation, the ribosome is attached to the 5’ end of an mRNA. the ribosome then moves along the mRNA molecule towards the 3’ end. in this way, translation is 5’ to 3’

Question 20

which bases are purine?

Answer 20

guanine and adenine are the purines (double ring structures)

Question 21

which bases are pyrimidine?

Answer 21

cytosine, thymine and uracil are pyrimidines (single ring structures)

Question 22

what are the consequences of purine to pyrimidine bonding on the structure of DNA?

Answer 22

when a pyrimidine is paired with a purine, the width dimension of both pairs is identical. this means that the DNA sugar-phosphate backbones have a consistent diameter throughout the entire molecule

Question 23

what is a nucleosome?

Answer 23

the basic structural unit of a DNA packaging is the nucleosome. a nucleosome consists of a length of DNA coiled around a core of eight proteins. these proteins are called histones.
histones are a family of small, positively charged proteins. due to the phosphate groups in nucleotides, DNA is negatively charged. DNA binds tightly to the histone proteins using electromagnetic attraction.
the H1 histone protein attaches to adjacent nucleosomes and binds DNA to the nucleosome core. the DNA wraps around the histones almost twice in each nucleosome

Question 24

why was the hershey-chase experiment done?

Answer 24

it was known that chromosomes were composed of both protein and DNA, but it wasn’t certain which was the genetic material. it was commonly thought that it was protein, due to the larger number of amino acids vs number of bases, but there was no evidence of this theory.
the hershey-chase experiment was done to determine whether DNA or proteins is the genetic material

Question 25

what is the procedure for the hershey-chase experiment?

Answer 25

radioactive sulphur (s-35) in protein coat, radioactive phosphorus (p-32) in DNA
1. bacteria infected by viruses (T2 bacteriophage) separately. viruses insert their DNA and the host cell replicates it
2. blend the bacterial culture
3. centrifuge the blend culture to concentrate the dense cells into a pellet
4. under the assumption that cells would contain the genetic material, measure the radioactivity of the supernatant and pellet

Question 26

what were the results of the hershey-chase experiment?

Answer 26

s-35 was found in the supernatant, p-32 was found in the pellet. therefore, genetic material is formed from DNA