Core Concept: Nucleic acids and their functions

Question 1

What is a nucleotide

Answer 1

monomer of a nucleic acid
contains a pentose sugar nitrogeneous base and a phosphate group

Question 2

What is a nucleic acid

Answer 2

polymers of nucleotides

Question 3

What are the two types of organic(nitrogenous) bases

Answer 3

purine and pyrimidine

Question 4

What reaction releases energy from ATP
What is the name of the enzyme that catalyses this

Answer 4

hydrolysis
ATPase

Question 5

What are the components of ATP

Answer 5

adenine base ribose sugar and three phosphates

Question 6

Why is ATP referred to as a universal energy currency

Answer 6

used to provide energy for all biochemical reactions in all living organisms

Question 7

Define phosphorylation

Answer 7

the addition of a phospahte group to a molecule

Question 8

Describe the formation and breakdown of ATP in terms of endergonic or exergonic

Answer 8

the formation of ATP is condensation reaction which is endergonic
the break down of ATP is hydrolysis which is exergonic

Question 9

Advantages of using ATP as an energy supplier instead of glucose directly

4 points

Answer 9

provides a useable small amount of energy when and where it is needed
one hydrolysis reaction that releases energy immediately whereas glucose involves many intermediates and takes longer for energy to be released
one enzyme needed to hydrolyse ATP but many needed for glucose
higher efficiency of ATP than glucose higher control by the cell

Question 10

Roles of ATP

5 points

Answer 10

Metabolic processes- build large complex molecules (DNA synthesis)
Active transport- to change the shape of carrier proteins
Movement - for muscle contraction
Nerve transmission - Na and K actively transported across axon membrane
secretion - the packaging and transport of vesicles

Question 11

Structure of DNA

Answer 11

double helix
antiparallel
long thin and tightly coiled molecule
comlimentary base pairs A,T,C,G
phosphate deoxyribose sugar backbone

Question 12

What are the complimentary base pairs of DNA
Are they purine or pyrimidine

Answer 12

adenine and thymine
cytosine and guamine
purine= adenine and guamine
pyrimidine= cytocine and thymine

Question 13

What bonds are between the bases

Answer 13

hydrogen bonds

Question 14

How is DNA suited for its function

4 points

Answer 14

stable so information passes unchanged from generation to generation
is long chain so holds alot of genetic informstion
two strands are able to seperate as they are held together by H bonds
double helix shape protects the genetic information on the inside

Question 15

The structure of RNA

Answer 15

single stranded
shorter than DNA
ribose sugar
AUCG bases

Question 16

Complimentary base pairs of RNA
Are they purine or pyrimidine

Answer 16

Adenine and Uracil
Cytosine and Guamine
purine= adenine and guamine
pyrimidine= cytocine and uracil

Question 17

Different types of RNA and their function

Answer 17

mRNA - carries genetic code from the DNA to the ribosomes
rRNA - component in ribosomes
tRNA- provides the ribosomes with specific amino acids for protein synthesis

Question 18

Differences between RNA and DNA

4 points

Answer 18

RNA is single stranded DNA is double stranded helix

RNA has Uracil DNA has Thymine

RNA is shorter DNA is longer

RNA has ribose sugar DNA has deoxyribose sugar

Question 19

Two main roles of DNA

Answer 19

Replication
Protein synthesis

Question 20

Process of DNA replication

Answer 20

DNA helicase breaks H bonds between bases(DNA is unzipped)
this exposes unpaired bases.
free DNA nucleotides bind to their comlementary base pairs on the template strand DNA polymerase binds these nucleotides together by condensation reactions between sugar and phosphate groups of adjacent nucleotides then 2 new DNA molecules are formed from 1 new and 1 old strand of the DNA.

Question 21

Define semi-conservative replication

Answer 21

Theory of DNA replication in which each strand of a parental double helix acts as a template for the formation of a new molecule, each containing an original, parental strand, and a newly synthesised, complementary daughter strand.

Question 22

Describe the process of the experiment that confirmed the semi-conservative replication theory

Answer 22

E.Coli DNA was placed ina culture medium comtaining a heavy nitrogen isotope (N15) and then left to replicate once
it was washed and transfeered to another culture medium of light nitrogen (N14) it was left to replicate 2 more times

upon the 1st round of replication (in N15) it was centrifuged the result was a band near the bottom of the centrifuge of high density
the 2nd round this was repeated and there was only one band in the middle of the centrifuge with a mid point density suggesting an even mix of N14 and N15. this disproved conservitive replication
the final round of replication there was a band in the middle where it was previously observed and a band higher up with less density suggeesting DNA strands of N14 only this disproved dispersive replication

Question 23

What are the other theories of DNA replication that were disproved by Meselsohn and Stahl’s experiment

2 points

Answer 23

dispersive- each new double helix synthesised contains fragments of new and old DNA
conservative- a whole new double helix is synthesised

Question 24

How many bases code for an amino acid
What is this called

Answer 24

three
its called a triplet code of DNA
once transcribed onto mRNA it is called a codon

Question 25

Characteristics of the genetic code

Answer 25

three bases encode for each amino acid there are 64 possible codes but only 20 amino acids the code is punctuated as there are codes that dont code for amino acids but are stop codons the code is universal code is non overlapping

Question 26

How many possible codes are there What does the suggest

Answer 26

64 because 4 bases triplet code is 3 so 4 to the power of 3 this suggests more than triplet code codes for the same amino acid

Question 27

What is a ‘stop’ codon

Answer 27

a codon that is at the end of the mRNA that does not code for a protein but codes for the end of the chain (ribosomes stops) synthesising

Question 28

What is meant by the code being universal and non-overlapping

Answer 28

one base is in one code the same 3 bases code for the same amino acid in every organism universally

Question 29

Define intron

Answer 29

non coding region of DNA

Question 30

Define exon

Answer 30

coding region of DNA

Question 31

What is the difference between DNA of a prokaryote and DNA of a eukaryote

Answer 31

DNA is in the nucleus in eukaryotes whereas in the prokaryote it is not DNA has introns in eukaryotes but prokayotic DNA does not only (Exons)

Question 32

Name the two stages of protein synthesis

Answer 32

Transcription Translation

Question 33

Describe the process of transcription

Answer 33

DNA helicase unzips a section (gene) of the DNA by breaking the hydrogen bonds between complementary base pairs. RNA polymerase links to the template strand of DNA and attaches mRNA nucleotides to their complementary base pairs, until a stop sequence / codon. The newly made premRNA then leaves the DNA. Post-transcriptional modification of the pre-mRNA takes place to remove the introns, leaving only exons in the mature mRNA. This leaves the nucleus via the nuclear pores to be translated into a protein in the cytoplasm.

Question 34

Describe the process of translation

Answer 34

mRNA is a linear chain of three base codons. There are complementary anticodons on tRNA molecules. When the mRNA leaves the nucleus, it attaches to the small subunit of a ribosome. The large subunits of a ribosome have 2 attachment sites for tRNA. The ribosome holds the mRNA and the tRNA (which have attached specific amino acids) in position for the amino acids to form peptide bonds and create a polypeptide chain. The codon on the mRNA therefore determines the tRNA as the tRNA which attaches must have a complementary 3 base code. called an anti codon. The tRNA that matches the codon on the mRNA has a specific amino acid attached to the 3’ end of the tRNA molecule. The ribosome moves along the mRNA holding each tRNA in place until the amino acid attaches. The tRNA then leaves, the ribosome moves along and the next tRNA attaches to the next codon. until a stop codon is reached

Question 35

How can polypeptides be further modified

Answer 35

they can be folded in the rough endoplasmic reticulum and can be modifeid in the golgibody by having lipid and sugar groups added