Module 2: Topic 2:3: Nucleotides and Nucleic Acids.

Question 1

What elements do Nucleotides consist of?

Answer 1

Carbon

Hydrogen.

Oxygen.

Nitrogen.

Phosphorus.

Question 2

What are nucleotides made from?

Answer 2

It is made from a pentose sugar , a nitrogenous base and a phosphate group

Question 3

What are nucleotides monomers of?

Answer 3

They are monomers of RNA and DNA.

(DNA & RNA are both types of nucleic acids)

Question 4

What are RNA and DNA used for?

Answer 4

DNA is used to store genetic information - The instructions for an organism to grow and develop.

RNA is used to make proteins from the instructions in DNA.

(They are both found in living things.)

Question 5

What does RNA and DNA stand for?

Answer 5

DNA = Deoxyribonucleic acid.

RNA = Ribonucleic acid.

Question 6

What are the 4 Nitrogenous bases for DNA?

Answer 6

Adenine, Thymine, Guanine, Cytosine.

Question 7

What are the 4 Nitrogenous bases for RNA.

Answer 7

Adenine, Uracil, Guanine, Cytosine.

Question 8

What are the two types of Bases in RNA and DNA?

Answer 8

Purines and Pyrimidines.

Question 9

What is the difference between Purines and Pyrimidines?

Answer 9

Purines contain 2 Carbon to Nitrogen rings joined together.

Whereas Pyrimidines contain only 1 Carbon to Nitrogen rings.

Question 10

Which Nitrogenous bases belong to Purines?

Answer 10

Adenine and Guanine.

They form 3 hydrogen bonds with each other.

Question 11

Which Nitrogenous bases belong to pyrimidines?

Answer 11

Cytosine and Thymine.

They form 2 hydrogen bonds with each other.

Uracil (RNA only)

Question 12

Explain the Polynucleotide structure?

Answer 12

Nucleotides join together to form Polynucleotides.

The nucleotides join up between the Phosphate group of one nucleotide and the sugar of another nucleotide via a condensation reaction.

Question 13

What is a Phosphodiester bond?

Answer 13

It is a covalent bond that forms when Nucleotides join together to form polynucleotides.

Polynucleotides can be broken down into nucleotides again by breaking the Phosphodiester bonds using hydrolysis reactions.

Question 14

Explain the sugar- phosphate backbone.

Answer 14

The chains of sugars and phosphates is known as the sugar- phosphate backbone.

It consists of a phosphate group and two ester bonds.

Question 15

Describe the structure of DNA.

Answer 15

DNA is composed of 2 polynucleotide strands joined together to form a double helix shape.

The two strands are anti-parallel as they have the sequence running in opposite directions.

Question 16

What are the differences between RNA and DNA?

Answer 16

DNA is found in chromosomes in the nucleus whereas RNA is found in the cytoplasm.

DNA is an extremely long molecule whereas RNA is a relatively short molecule.

DNA has the pentose sugar called deoxyribose (one less oxygen atom) whereas RNA has the pentose sugar Ribose.

DNA has hydrogen bonds between the two complementary strands .

RNA contains Uracil instead of thymine.

Question 17

What are Phosphorylated nucleotides and give examples.

Answer 17

To phosphorylate a nucleotide, you add one or more phosphate groups to it.

ADP and ATP are examples of phosphorylated nucleotides.

Question 18

What are the structures for ADP and ATP?

Answer 18

ADP stands for adenosine diphosphate and it contains the base adenine, the sugar ribose and two phosphate groups.

The structure for ATP consists of ribose sugar and adenosine (base) attached to 3 phosphate groups.

Question 19

Explain how ATP is used in Respiration.

Answer 19

Plants and animal cells release energy from glucose- this is called respiration.

A cell cannot get its energy directly from glucose , so in respiration, the energy released from glucose is used to make ATP and then the molecules of ATP provide energy from the chemical reactions in the cell.

Question 20

Describe the hydrolysis reaction of ATP.

Answer 20

When water is added, ATP is broken down into adenosine diphosphate and an inorganic phosphate (Pi).

The reaction is catalysed by the enzyme ATP hydrolase

Question 21

What is the word equation for the hydrolysis of ATP?

Answer 21

ATP + water = ADP + Pi + energy

This reaction is catalysed by the enzyme ATPase /ATP hydrolase

Question 22

Describe the practical For DNA purification.

Answer 22

DNA can be purified using a precipitation reaction.

First blend the fruit to break the cells apart.

Mix together detergent , salt , distilled water and the blended up fruit in a test tube.

This is because the detergent breaks down the cell membrane to release the cells DNA. and the salt binds to the DNA, causing it to clump together.

Place in a water bath at 60 degrees Celsius for 15 minutes, this will denature the enzymes and stooping them from degrading the DNA.

Place in an ice bath to cool the test tube down and then filter the mixture.

Transfer a sample to a fresh test tube.

Add proteases to the test tube – these break down proteins (histones) bound to the DNA.

Slowly add cold ethanol so that it forms a layer on top of the mixture.

The DNA will precipitate out of the solution and can be removed with a glass rod.

Question 23

Why does DNA replicate?

Answer 23

DNA replication occurs before the cell divides.

DNA replicates itself during the S phase of the cell cycle so that each daughter cells has a copy of the DNA after cell division.

DNA replication mean that parents can pass their DNA to their offspring.

Question 24

What is semi-conservative DNA replication?

Answer 24

When DNA is replicated, the new DNA molecule consists of one strand that is freshly made DNA and the other strand is from the original DNA that was copied

Since half of the DNA is preserve from the previous round of replication, we call this process semi-conservative.

Question 25

Describe the process of DNA replication.

Answer 25

1) DNA helicase unwinds the double helix, this breaks the hydrogen bonds between complementary base pairs to separate the strands. one of the strands will act as a template for synthesis of the other strand.

2) Complementary nucleotides will attach to the template strand by hydrogen bonding.

DNA polymerase then catalyses the formation of phosphodiester bonds between nucleotides, forming a complementary strand alongside the template parent strand.

Two daughter DNA molecules are formed, each containing half of the original DNA double helix.

Question 26

Why is DNA polymerase important?

Answer 26

DNA polymerase must accurately copy the template strand to avoid placing the wrong DNA nucleotide in the wrong position.

To avoid this, DNA polymerase proof reads the complementary strand as it moves along the DNA and if it detects a mismatch, it can ship out the wrong nucleotide and replace it with the right one.

It has an accuracy rate of 99%. This means that mistakes do occur every once in a while.

Question 27

What is a mutation?

Answer 27

A mutation is a change to the DNA base sequence.

A DNA mutation can have detrimental effects to the organism, since an altered base sequence can change the sequence of amino acids in a protein, causing it to fold differently and possibly lose its function.

Question 28

What are the different types of RNA?

Answer 28

Messenger RNA - mRNA

Transfer RNA - tRNA

Ribosomal RNA - rRNA

Question 29

What is RNA?

Answer 29

It is a single polynucleotide strand and it contains uracil as a base instead of thymine.

Question 30

Describe the function of mRNA.

Answer 30

It is a single polynucleotide strand and is produced during transcription.

It carries the genetic code from the DNA in the nucleus to the cytoplasm, where it is used to make a protein in translation.

Groups of three adjacent bases are called codons.

Question 31

Describe the function of tRNA.

Answer 31

It is a single polynucleotide strand that is folded into a clover shape.
It carries amino acids to the ribosomes during translation.

It contains an amino acid binding site at one end and an anti-codon at the opposite end.

It is found in the cytoplasm where it is involved in translation.

It carries the amino acids that are used to make proteins to the ribosomes.

Question 32

Describe the function of rRNA.

Answer 32

It associates with proteins to form two subunits that make up the ribosome.

The ribosome moves along mRNA during protein synthesis.

The rRNA in the ribosome helps to catalyse the formation of peptide bonds between amino acids.

Question 33

What is a triplet code?

Answer 33

It is three nucleotide bases that make up a codon, which codes for a particular amino acid.

Question 34

What is a non-overlapping code?

Answer 34

The codons do not overlap.

Once the ribosome has ‘read’ one codon, the ribosome will move onto the next.

Question 35

What is a universal code?

Answer 35

This is the idea that all organisms use the same genetic code.

Question 36

Describe the genetic code?

Answer 36

The genetic code is the sequence of base triplets (codons) in DNA or mRNA, which codes for specific amino acids.

In the genetic code, each base triplet is read in a sequence, separate from the triplet before it and after it- base triplets do not share their bases, they are non-over lapping.

The genetic code is degenerate - different codons can code for the same amino acid. For example, the codons CUU and CUC both code for the amino acid leucine. This means that some mutations will have no effect on the organism since the same protein will still be produced.

Question 37

Do all triplets code for amino acids?

Answer 37

No.

Some triplets are used to tell a cell when to stop the production of a protein. these are called STOP SIGNALS.

They are found at the end of mRNA

Question 38

What are the two stages of Protein synthesis?

Answer 38

Transcription and Translation.

Question 39

Describe the process of Transcription.

Answer 39

1) The enzyme RNA polymerase attaches to the DNA double helix. The hydrogen bonds between the two DNA strands break, separating the strands. The DNA double helix uncoils and one of the strands is used as a template to make an mRNA copy.

2) The RNA polymerase lines up free floating RNA nucleotides alongside the template strand. Complementary base pairing occurs through the formation of phosphodiester bonds. Once the RNA nucleotides have paired up with their specific bases on the DNA strand, they are joined together by RNA polymerase, forming an mRNA strand.

3) The RNA polymerase moves along the DNA, assembling the mRNA strand. The hydrogen bonds between the uncoiled strands of DNA reform once the RNA polymerase has passed by and the strands coil back into a double helix.

4) When RNA polymerase reaches a stop codon, it stops making mRNA and detaches from the DNA. The mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where Translation will next take place.

Question 40

Describe the process Translation.

Answer 40

This process takes place at the ribosomes in the cytoplasm.

The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to the ribosome.

A tRNA molecule, with an anticodon that is complementary to the start codon on the mRNA, attaches itself to the mRNA by complementary base pairing. A second tRNA molecule attaches itself to the next codon on the mRNA in the same way.

rRNA in the ribosome catalyses the formation of the peptide bond between the two amino acids attached to the tRNA molecules. this joins the amino acids together. The first tRNA molecule moves away, leaving its amino acid behind.

A third tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first two and the second tRNA molecule moves away.

The process continues, producing a chain of linked amino acids, until there is a stop codon on the mRNA molecule.

The polypeptide chain, protein, then moves away from the ribosome and translation is complete.