A1.2 Nucleic Acids

Question 1

what does a nucleotide consist of?

Answer 1

pentose sugar, phosphate, nitrogenous base

Question 2

one-ring bases in DNA

Answer 2

pyrmidines-C and T(or C and U for RNA)

Question 3

2-ring bases in DNA

Answer 3

purines-A and G

Question 4

what does the sugar-phosphate backbone allow for?

Answer 4

bc it is covalently bonded, it gives strength to DNA and RNA helping them to store info reliably for long periods

Question 5

describe the structure of DNA

Answer 5

2 DNA polynucleotide strands join via hydrogen bonds between bases, there’s complimentary base pairing, 2 polynucleotide strands twist to form double helix

Question 6

what are the 3 differences between DNA and RNA?

Answer 6

in DNA there’s deoxyribose in RNA theres ribose; DNA has thymine RNA has uracil; RNA is single stranded DNA is double stranded

Question 7

what are the 3 roles of complementary base pairing?

Answer 7

DNA replication, transcription, translation

Question 8

complementary base pairing in DNA replication

Answer 8

sequences of bases in DNA can be copied accurately so the genetic info of a cell can be passed onto daughter cells

Question 9

complementary base pairing in transcription

Answer 9

RNA can be made with the same base sequence as 1 of the 2 strands of DNA. mRNA carries base sequence of a protein-coding gene to the ribosome

Question 10

complementary base pairing in translation

Answer 10

base sequences can be used to determine the amino acid sequence in a polypeptide. mRN carries a series of 3-base codons. each tRNA has one 3-bade anticodon and carries 1 amino acid. ribosomes link codons to anticodons by complementary base pairing allowing the base sequence of every codon to be translated into a specific amino acid in a polypeptide

Question 11

what does the universality of the genetic code suggest?

Answer 11

that all life evolved from the same original ancestor with minor differences added since then

Question 12

what does having one purine and one pyrimidine base do?

Answer 12

means the 2 base pairs are of equal width and need the same distance between the 2 sugar-phosphate backbones in the double helix meaning DNA structure is stable

Question 13

what is a nucleosome used for?

Answer 13

allows DNA to supercoil

Question 14

describe the structure of a nucleosome

Answer 14

each nucleosome has a core of 8 histone proteins with a DNA wound round twice and one more histone securing the structure. some linker DNA between adjacent nucleosomes

Question 15

what was the hershey-chase experiment trying to investigate?

Answer 15

whether genes were made of DNA or protein

Question 16

explain reasons behind why they used T2

Answer 16

viruses like T2 consist only of DNA and protein so their genes must be made of one of these materials. DNA has phosphorus but not sulfur and protein has S not P

Question 17

explain the Hershey-Chase experiment and its results

Answer 17

write

Question 18

what was Chargaff’s data?

Answer 18

purines(A+G)=50% and pyrimidines(T+C)=50%

Question 19

what did Crick and Watson discover about Chargaff’s data and about Frankilin and Wilkins’s data?

Answer 19

they made semi-conservative model of DNA replication; created cardboard and metal shapes to represent components of DNA; uncovered complementary base pairing bc joined strands must have a consistent width-strands must be anti-parallel

Question 20

why did some scientists doubt that DNA carried the genetic code when it was first discovered?

Answer 20

because DNA’s chemical composition is relatively simple and thought it was proteins instead bc they are more complex

Question 21

what is RNA’s function in a cell?

Answer 21

RNA transfers genetic info from DNA to ribosomes, RNA also makes up part of the ribosomes themselves

Question 22

how do nucleotides join together to form a polynucleotide strand?

Answer 22

nucleotides join via condensation reactions between phosphate group of one and the sugar of another which forms a polynucleotide strand, with phosphodiester bonds between nucleotides

Question 23

name 2 types of reaction in which water is a metabolite

Answer 23

condensation+hydrolysis, metabolite is a substance involved in a metabolic reaction

Question 24

why is DNA a stable molecule?

Answer 24

phosphodiester backbone protects the more chemically reactive nitrogen containing organic bases inside the double helix; hydrogen bond form bridges between bases

Question 25

why is replication being semi-conservative important?

Answer 25

ensures genetic continuity between generations of cells meaning genetic info is passed from one generation to the next

Question 26

what are the stages of DNA replication?

Answer 26

DNA helicase unwinds and separates DNA strands by breaking hydrogen bonds; DNA polymerase links nucleotide triphosphates(3 nucleotides)to the template strands using complementary base pairing; 2 identical copies wind back to form double helices

Question 27

why is DNA replication called semi-conservative?

Answer 27

new daughter molecules each consist of a parent molecule strand of DNA which is the template allowing nucleotides to bond with complementary base and a new double stranded DNA is formed

Question 28

ATP

Answer 28

adenosine triphosphate=ribose, adenine and 3 phosphate groups

Question 29

when is energy released?

Answer 29

when ATP is hydrolysed to form ADP and a phosphate molecule-process is catalysed by ATP hydrolase. the energy comes from the bonds between the phosphate molecules, bonds unstable and have low activation energy so breaking them is quick and releases a lot of energy

Question 30

what produces ATP during photosynthesis and respiration?

Answer 30

condensation of ADP and inorganic phosphate catalysed by ATP synthase

Question 31

properties of ATP

Answer 31

immediate source of energy and is more desirable to use than glucose bc ATP can be broken down in a single step to release lots for energy; isn’t stored in large quantities as it can easily be reformed from ADP; used in lots of ways eg metabolic processes, movement, active transport

Question 32

what did franklin and wilkins discover?

Answer 32

used x-ray diffraction to reveal the double helix structure of DNA

Question 33

what is transcription?

Answer 33

synthesis of mRNA from DNA

Question 34

describe the process of transcription

Answer 34

RNA polymerase unwinds the double helix and separates the strands; RNA polymerase binds free nucleotide triphosphates via complementary base pairing(uracil instead of thymine); mRNA strand separates from DNA and DNA reforms its double helix

Question 35

what is translation?

Answer 35

synthesis of protein from the mRNA strand at the ribosome

Question 36

describe the process of translation

Answer 36

mRNA strand binds to a ribosome; tRNA molecule binds to mRNA strand via hydrogen bonds using its anticodon which is complementary to a specific codon; once bound a 2nd tRNA binds to the next codon; ribosome forms a peptide bond between adjacent amino acids; first tRNA detaches and ribosome moves along mRNA to next codon; process if repeated creating a polypeptide; translation stops and polypeptide is free to detach

Question 37

why is prokaryotic DNA naked(non-protein associated)?

Answer 37

means it does not wrap around histones

Question 38

what is a proteome?

Answer 38

the entire set of proteins expressed by an organism at a certain time