2.1 Structure of RNA and DNA

Question 1

Describe the basic function of DNA and RNA in all living cells

Answer 1

DNA: Holds genetic information which codes for polypeptides (proteins)
RNA: Transfers genetic information from DNA to ribosomes

Question 2

Name the types of molecules from which a ribosome is made

Answer 2

RNA and Proteins

Question 3

Draw (use ur imagination) a nucelotide

Answer 3

Phosphate group(circular)
Pentose-either deoxyribose or ribose- (pentagonal shape)
Nitrogenous base (Rectangle)

Question 4

What is the monomer that makes up DNA

Answer 4

A nucleotide

Question 5

What are the 4 nitrogenous bases in DNA

Answer 5

Guanine
Cytosine
Adenine
Thymine

Question 6

What is the polymer form of a nucelotide

Answer 6

Polynucelotide

Question 7

Describe how nucleotides join together to form polynucleotides (3)

Answer 7

• Condensation reactions, removing water molecules
  ● Between phosphate group of one nucleotide and deoxyribose / ribose of another
  ● Forming phosphodiester bonds

Question 8

How is the polynucelotide held together

Answer 8

Strong covalent bonds called phosphodiester bonds

Question 9

How are the DNA polymer pairs joined together

Answer 9

Hydrogen bonds between the Nitrogenous bases

This is how the double helix strcutre is created as the two chains twist

Question 10

What is the only condition through which hydrogen bonds form in polynucelotides

Answer 10

They can only form between complimentary base pairs
Cytosine—Guanine
Adenosine–Thymine
Guanine—Cytosine
Thymine–Adenine

Number of ‘-‘ represent the number of h bond bwteen the bases

Question 11

How does the structure of DNA relate to its function (7)

Answer 11

● Two strands → both can act as templates for semi-conservative replication
● Hydrogen bonds between bases are weak → strands can be separated for replication
● Complementary base pairing → accurate replication
● Many hydrogen bonds between bases → stable / strong molecule
● Double helix with sugar phosphate backbone → protects bases / hydrogen bonds
● Long molecule → store lots of genetic information (that codes for polypeptides)
● Double helix (coiled) → compact

Question 12

Why did many scientists initially doubt that DNA carried the genetic code

Answer 12

DNA was relatively simple- Chemically simple molecules with few components

Question 13

What is RNA (3)

Answer 13

*A polymer of a nucleotide formed of a:
Ribose
Nitrogenous base
Phosphate group
*Relatively short
*Single Stranded

Question 14

Name the 4 nitrogenous bases in RNA

Answer 14

Adenine
Uracil
Guanine
Cytosine

Question 15

What is the function of RNA

Answer 15

To copy and transfer the genetic code from the DNA in the nucleus to the ribosomes

Question 16

What are the three types of RNA

Answer 16

mRNA-Messenger
tRNA-Transfer
rRNA-Ribosomal

Question 17

What is mRNA

Answer 17

A copy of a gene from DNA
Created in the nucleus

Question 18

What is the function of mRNA

Messenger

Answer 18

To carry a copy of the genetic code of one gene to a ribosome in the cytoplasm

Question 19

Why is the function of mRNA important

Answer 19

DNA is too large to leave the nucleus and would be at risk of being damaged by enzymes —-> therefore destroying the genetic code permanently

Question 20

Why is mRNA short

Answer 20

It is the length of one gene so it can therefore leave the nucleus

Question 21

Why is mRNA short lived

Answer 21

It is only needed temporarily to help create a protein —> therefore by the time an enzyme breaks it down it would have already carried out its function

Question 22

What is a codon

Answer 22

Three bases in a gene that code for specific amino acids

Question 23

Where is tRNA found

Answer 23

in the cytoplasm

Question 24

What is the structure of tRNA

Answer 24

Single stranded but folded to create a shape that looks like a clover leaf that is held in place by H bonds

Question 25

What is the function of tRNA

Answer 25

To attach to one of the 20 amino acids and transfer this amino acid to the ribosome to create the polypeptide chin

Question 26

Do random amino acids bind to random tRNA (3)

Answer 26

* No * Specific amino acids bind to specific tRNA's * This is determined by the three bases found in the tRNA

Question 27

How are mRNA and tRNA similar(codon-anticodon)

Answer 27

The three bases found in the tRNA are complimemtary to mRNA and these are called anti codon

Question 28

What is the function of rRNA

Answer 28

To combine with proteins to make ribosomes

Question 29

What are the differences between the DNA and RNA monomers

Answer 29

* DNA contains the base Thymine whereas RNA has Uracil instead of Thymine * DNA contains the pentose suagr deoxyribose whilst RNA contains Ribose

Question 30

What are the two differences between the polymers of DNA and RNA

Answer 30

* DNA is much longer as it contains 23,000 genes whereas RNA is shorter as it only contains 1 * DNA is double stranded whilst RNA is single stranded

Question 31

Describe the structure of mRNA (5)

Answer 31

* Polymer of nucleotides * Each nucelotide formed from ribose, a phosphate group and a nitrogen base containing organic base * Bases are Uracil Adenine Cytosine Guanine * Phosphodiester bonds join adjacent nucelotides * Single helix

Question 32

Describe the structure of DNA (6)

Answer 32

* Polymer of nucelotide * Each nucelotide formed from deoxyribose, a phosphate group and a nitrogen containing organic base * Phosphodiester bonds join adjacent nucelotides * 2 polynucelotide chains held together by hydrogen bonds * Between specific complimentary base pairs- Adenine/Thymine Cytosine/Guanine * Double helix

Question 33

Compare and contrast the structure of DNA and mRNA (5)

Answer 33

-DNA Pentose sugar is deoxyribose whereas in mRNA the pentose sugar is ribose -DNA has the base thymine whereas in mRNA the base has no thymine but has Uracil instead -DNA is double stranded whilst mRNA is single stranded -DNA is longer (more nucelotides) mRNA is shorter (less nucelotides) -DNA has hydrogen bonding mRNA does not

Question 34

Which Nitrogenous bases are Purine

Answer 34

Adenine and Guanine They both have two rings Guanine has a double bond to O

Question 35

Which Nitrogenous bases are pyrimidine

Answer 35

Thymine Cytosine and Uracil Has one ring

Question 36

Why can Adenine and Cytosine not bond

Answer 36

Adenine would form 2 hydrogen bonds whereas Cytosine would form 3 hydrogen bonds

Question 37

What is the differnece between Deoxyribose and Ribose

Answer 37

Deoxyribose chemical formula-C5 H10 O4 Ribose has the same but one more oxygen Strcture of Deoxyribose is more stable so it has a sotrnger covalent bonds as the C3 bond will be bonded directly oto the phosphate group

Question 38

How are polynucleotides formed

Answer 38

When DNA contains a second antiparallel chain that runs in the opposite direction | E.g. 5' prime and 3' prime end

Question 39

Why is DNA stable

Answer 39

* The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix * Hydrogen bonds link the organic base pairs forming bridges

Question 40

Suggest how you can use incomplete information about the frequency of bases on DNA strands to find the frequency of other bases

Answer 40

1. % of adenine in strand 1 = % of thymine in strand 2 (and vice versa) 2. % of guanine in strand 1 = % of cytosine in strand 2 (and vice versa) Because of specific complementary base pairing between 2 strands