Nucleotides and Nucleic acid

Question 1

Who discovered the DNA helix structure and who received the credit?

Answer 1

Rosalind Franklin used X-ray diffraction to identify the structure of DNA

James Watson and Francis Crick too the findings and shared them to get credit

Question 2

What is a nucelotide?

Answer 2

A monomer of nucleic acid that is made of a nitrogenous base, a phosphate group and a pentose sugar

Question 3

What type of sugar is found in DNA and RNA?

Answer 3

DNA uses a deoxyribose sugar

RNA uses a ribose sugar

Question 4

How do polynucleotides form?

Answer 4

A condensation forms an ester bond between an oxygen on the phosphate group and carbon 3 on the hydroxy group (named pentose sugar)

Question 5

Name the 5 nitrogenous bases and their 2 types

Answer 5

Purine- Adenine, guanine

Pyrimidine- Thymine, cytosine, uracil

Question 6

What bases are used for DNA and RNA?

Answer 6

DNA- Adenine, Guanine, Thymine, Cytosine

RNA- Adenine, Guanine, Uracil, Cytosine

Question 7

How many bonds are formed between the DNA strands and what bond are they?

Answer 7

Hydrogen bonds are formed

Between Adenine and Thymine 2 bonds are formed

Between Guanine and Cytosine 3 bonds are formed

Question 8

What is uracil?

Answer 8

It is the nitrogenous base that replaces Thymine in the RNA during transcription and translation

Question 9

Define and explain the term anti-parallel

Answer 9

Anti-parallel refers to a double helix having opposite facing strands(one goes up and the other goes down)

This is needed to happen in order for complementary base pairing to occur and creates the double helix structure

Question 10

How often does the DNA chain twist?

Answer 10

Every 10 nucleotides which is approximately 0.34nm and helps create the double helix

Question 11

Describe the process for DNA replication

Answer 11

1)The semi-conservative replication of DNA occurs in the nucleus,
2)The double helix is unwound by the enzyme gyrase,
3)The hydrogen bonds are broken by the enzyme DNA helicase,
3)Each strand acts as a template to allow for free DNA nucleotides within the nucleus to align with the exposed nucleotides on the strand,
4)Complementary base pairing occurs which leads to 2 hydrogen bonds forming between A and T and 3 hydrogen bonds forming between G and C,
5)Phosphodiester bonds form between the oxygen in the phosphate group of one nucleotide and carbon 3 of the deoxyribose sugar above using the enzyme DNA polymerase,
6)This creates the sugar-phosphate backbones which gives the DNA its structure,
7)The whole process results in 2 identical strands of DNA that each contain half new DNA and half original DNA

Question 12

Why is it called ‘semi-conservative’ DNA replication?

Answer 12

It is known as semi-conservative because semi means half and after the process half of the original DNA has been conserved in the strand but the other half is new

Question 13

Where else does semi-conservative replication take place?

Answer 13

Bacteria- The nucleoid and plasmids

Chloroplasts and mitochondria- Their plasmids undergo semi-conservative replication

Question 14

Explain what protein synthesis is

Answer 14

The production of a chain of amino acids from a gene through the transcription of a gene into a strand of mRNA and the translation of the mRNA strand into a polypeptide chain

Question 15

Describe the process for protein synthesis and secretion

Answer 15

1) An mRNA copy of the gene is made in the nucleus and then levs the nucleus through a nuclear pore,
2) The mRNA attaches to a ribosome which reads the gene and then assembles the protein,
3) Molecules of the protein are pinched off in vesicles and move towards the golgi apparatus and then fuse with it,
4) The golgi apparatus processes and packages the molecules which are then pinched off in vesicles and move to the cell surface membrane,
5) The vesicle fuses with the membrane which then opens and releases molecules

Question 16

How does RNA differ from DNA?

Answer 16

RNA uses ribose as opposed to deoxyribose,

RNA uses the base uracil as opposed to thymine,

RNA has single stranded polynucleotides as opposed to double stranded,

RNA exists in the three form mRNA, rRNA and tRNA as opposed to DNA which is singular

Question 17

Describe messenger RNA (mRNA)

Answer 17

It is a copy of a DNA template strand

It has 3 adjacent codons which are nucleotides that code for amino acids,

It is used in transcription and translation

It is made in the nucleolus and moves to a ribosome as a template for protein synthesis

Question 18

Describe ribosomal RNA (rRNA)

Answer 18

A complex molecule that accounts for half the mass of a ribosome,

Forces tRNA and mRNA process and translate genes into proteins

It is used in the process of translation

Question 19

Describe transfer RNA (tRNA)

Answer 19

Small and single stranded

It has a binding site for a specific amino acid

It has an unpaired triplet of bases called an anticodon

It carries an amino acid to a ribosome where they are bonded together to form a polypeptide

Question 20

Define and describe the process of transcription

Answer 20

Transcription is the process of an mRNA making a copy of a gene

1) The gene to be transcribed unwinds via the enzyme gyrase,
2) The hydrogen bonds are then broken by the enzyme helicase,
3) One DNA strand acts as a template to allow free RNA nucleotides to bind to the complementary bases,
4) Hydrogen bonds then form with 3 forming between G and C, 2 forming between U-A and A-T because uracil replaces thymine as a base in RNA
5) RNA polymerase then catalyses the formation of phosphodiester bonds (covalent) between the nucleotides,
6) The bonds attach from the phosphate group of one nucleotide to carbon 3 of the pentose sugar of another,
7) The mRNA is complementary to the template strand but not identical,
8) The mRNA is then released from the DNA and leaves the nucleus through a nuclear pore to the ribosome

Question 21

Define and describe the process of translation

needs work

Answer 21

Translation is the process of an mRNA being converted into a chain of amino acids on a ribosome

1) mRNA bonds to a ribosome where a tRNA attaches and its anticodon binds to the first codon on the mRNA through complementary base pairing,
2) The tRNA is carrying a specific amino acid,
3) The 2nd tRNA then bonds to the 2nd exposed codon with its anticodon (there is room for two codons to attach at once),
4) A peptide bond then forms between the 2 amino acids,
5) mRNA moves along the ribosome,
6) A 3rd tRNA brings another amino acid as the first tRNA leaves to collect another amino acid,
7) The process continues until a stop codon is reached

Question 22

What are the three key characteristics of the genetic code?

Answer 22

It is:
Universal- All living organisms use the same code

Degenerate- For most amino acids there is more than one base triplet

Non-overlapping- It is read starting from a fixed point in groups of three

Question 23

What is the structure of ATP?

Answer 23

A nitrogenous base of Adenine is attached to a ribose sugar which is attached to three phosphate groups

Question 24

What is the structure of ADP?

Answer 24

A nitrogenous base of Adenine is attached to a ribose sugar which is attached to two phosphate groups

Question 25

How is ADP formed?

Answer 25

An ATP molecule undergoes a hydrolysis reaction which results in the formation of ADP and Pi (phosphate group)

This process also releases energy and occurs during respiration