Nucleic acids

Question 1

What is the general structure of a nucleic acid

Answer 1

• pentose sugar
• phosphate group
• nitrogenous base

Question 2

What is ATP

Answer 2

• three phosphate groups, ribose sugar, adenine
• ATP is formed from an endergonic reaction in respiration
• 30.6KJ of energy is stored in this bond and released when it is hydrolysed into ADP and inorganic phosphate

Question 3

What is the advantages of ATP

Answer 3

• universal energy currency provide energy fro all biochemical reactions in all living organisms
• ATP releases energy in one hydrolysis reaction controlled by one enzyme
• ATP releases energy in small usable amounts
• ATP travels easily to where it may be used for secretion, muscle contraction , nerve tranmission or active transport

Question 4

What is RNA

Answer 4

• phosphate, ribose and nitrogenous base (A,U,C,G)
• RNA nucleotide linked together in a single stranded polynucleotide

Question 5

What is mRNA

Answer 5

• made a a complementary copy of DNA genetic code in the nucleus during transcription
• molecule length is related to the length of the gene transcribed
• it attatched to a ribosome in the cytoplasm

Question 6

What is rRNA

Answer 6

• forms ribosomes

Question 7

What is tRNA

Answer 7

• carries amino acid at 3’ end and an anticodon arm to attach to the mRNA

Question 8

What is the structure of DNA

Answer 8

• phosphate, deoxyribose, nitrogenous base (A,C,T,G)
• made ofrom one strand of nucleotides linked by hydrogen bonds between bases to another strand that run antiparallel to the first

Question 9

What are the two types of bases

Answer 9

• purines - adenine and guanine
• pyrimidines - cytosine and thymine
• pair up with hydrogen bonds A pair with T C pairs with G
• complementary bast pair links the two strands a double helix is formed

Question 10

What is the differences between RNA and DNA

Answer 10

RNA
* ribose sugar
* single stranded
* A, U, C and G
* short polynucleotides
DNA
* deoxyribose ugar
* double stranded
* A,T,C and G bases
* long polynuclotides

Question 11

Why does DNA replicate

Answer 11

• when cells divide to form new cells they must reveive a copy of DNa
• therefore chromosomes must be able to make exact copies of themselves

Question 12

How does DNA replicate

Answer 12

• DNA helicase breaks the hydrogen bonds between the bases in the double helix
• this unwinds DNA and exposes unpaired bases
• Free nucleotides in the nucleoplasm are bound to their complementary bases on the unzipped strand
• DNA polymerase joins the nucleotides together by condensation reactions between sugar and phosphate groups of adjacent nucleotides
• Eventually 2 new DNA molecules are formed from 1 new and 1 old strand of DNA this is semi conservative replication

Question 13

Describe the Meselson and Stahl experiment

Answer 13

• grow bacteria with a heavy isotope of nitrogen centrifuge a sample a heavy band is seen
• remove bacteria with heavy DNA and place into a medium with light nitrogen and allow bacteria to divide. They will synthesise DNA with the nitrogen isotope available meaning their DNA will contain one N14 and one old N15 strand making it intermediate in densitry when centrifuged
• allow 1 moew generation to grow and the hybrid strands will now be copied by semi conservative creating 50% hybrid and 50% light DNA
• If grown for a further generation increase in light DNA

Question 14

Describe conservative replication and how it was rules out of Meselson and Stahl experiments

Answer 14

• direct copying of nucleotide sequence onto a new double stranded molecule whcih would give one light and one heavy molecule in generation 1

Question 15

Describe dispersive replication and how it was rules out of Meselson and Stahl experiments

Answer 15

• where half the nucleotides are placed randomly in the DNA being replicated to make new molecules which would successivley lighter molecules and therefore a band between hybrid and light in generation 2

Question 16

What is the genetic code

Answer 16

• three bases code for a specific amino aicd
• it is linear
• universal code
• for production of polypeptides

Question 17

Describe the process of transcription

Answer 17

• Dna helicase unzips a section (gene) of the DNA by breaking the hydrogen bonds between complementary base pairs
• RNA polymerase links to the template (coding) strand of DNA and attaches mRNA nucleotides to their complememntary base pairs A to U and C to G
• this copying stops at a stop codon
• the newly made pre mRna then leaves DNa
• post transcriptional modification of the pre mRNA taks place to remove non coding intron leaving only the coding section exons in mature mRNA this leaves the nucleus to be translated into a protein in thecytoplasm

Question 18

Why is the triplet code degeneraate

Answer 18

• 64 possible triplet codes for four bases
• some amino acids have more than one code
• this is why the code is termed degenerate
• a change in code does not always mean a change in amino acid

Question 19

Describe translation

Answer 19

• mRNa is a linear chain of three base codons there are complementary anticodons on tRNA molecules
• when mRNA leaves the nucleus it attatches to the small subunit of a ribosome
• large subunits of a ribosome have 2 attatchment sites for tRNA. The ribosome holds the mRNA and tRNA which have attatched amino acids in position for the amino acids to form peptide bonds and create a polypeptide chain
• the codon on the mRNa 3 bases determines the tRNa that attatches that mut have complementary 3 base code
• the tRna that matches the codon on the mRNa has a specific amino acid attatched to 3’ end of the tRNA molecules the ribosome moves along mRNA holding each tRNA in place until amino acid attaches
• the tRNA then leaves the ribosome moves along and the next tRNA attatches to the next codon

Question 20

How are new polypeptides modified

Answer 20

• addition of carbohydrates and lipids or phosphates or can be combined
• eg haemoglobin