2.3 DNA

Question 1

What are histone proteins?

Answer 1

A protein which DNA wraps around to form chromosomes.

Question 2

What are the four bases and state whether they are purine or pyrimidine

Answer 2

Adenine (purine) base
Thymine (pyrimidine) base
Guanine (purine) base
Cytosine (pyrimidine) base

Question 3

What is a purine and what bases are purines?

Answer 3

It is a type of nitrogen base found in DNA that consists of 2 nitrogen-carbon rings.
-Adenine and guanine

Question 4

What is a pyrimidine and what bases are pyrimidines?

Answer 4

It is a type of nitrogen base found in DNA which consists of only one nitrogen-carbon ring.
-Thymine
-cytosine
(both contain a Y like pyrimidine does)

Question 5

What type of bonds join together nitrogenous bases?

Answer 5

Hydrogen bonds

Question 6

What are the rules behind drawing the skeletal formula of a base?

Answer 6

Corner = carbon
carbon = 4 bonds
nitrogen = 3 bonds
hydrogen = 1 bond

Question 7

How many bonds does guanine and cytosine have when joined?

Answer 7

three

G C Three

Question 8

How many bonds do adenine and thymine have when joined?

Answer 8

two

A T Two

Question 9

What is an ester bond?

Answer 9

A bond found in lipids such as triglycerides

Question 10

What is a glyosidic bond?

Answer 10

A bond that joins the pentose sugar to its base within the nucleotide

Question 11

Outline the stages of DNA replication

Answer 11

1) DNA unwinds, catalysed by the gyrase enzyme.
2) The DNA is then unzipped bonds broken. Catalysed by DNA Helicase.
3) Free phophorylated nucleotide’s bond to the exposed complementary bases, catalysed by DNA Polymerase.
4) The leading strand is synthesised continuously whereas the lagging strand is in fragments which is later joined by ligase enzymes.

Question 12

What is a phosphorylated nucleotide?

Answer 12

A nucleotide with three phosphate groups attached.

Question 13

What is a gene?

Answer 13

A length of DNA that codes for a polypeptide or a length of RNA that is involved in regulating gene expression.

Question 14

What is a polypeptide?

Answer 14

A polymer made of many amino acid units joined together by peptide bonds.

Question 15

What was the conservative DNA replication theory?

Answer 15

The original molecule acts as a template and a new molecule is made.

Question 16

What is the dispersion DNA replication theory?

Answer 16

The original molecule breaks up into nucleotide’s, each one joins to a complementary nucleotide and new ones join up again

Question 17

What is the semi-conservative DNA replication theory?

Answer 17

This is the accepted theory. The new molecule consists of one original strand and one newly formed strand.

Question 18

What Is RNA?

Answer 18

A similar molecule to DNA and is used to in protein synthesis as a messenger of genetic information to the ribosomes.

Question 19

What is different between RNA and DNA?

Answer 19

• replaces the base thymine with uracil
• is only a single strand helix (can fit through nuclear pores)
• the pentose sugar in DNA is DEOXYRIBOSE but in RNA it is just RIBOSE.

Question 20

What is mRNA?

Answer 20

Messenger RNA
It encodes the amino acid sequence of a polypeptide.
It is the chain created when the RNA nucleotides join together.

Question 21

What is tRNA?

Answer 21

Transfer RNA

It brings the amino acid to the ribosomes during translation.

Question 22

What is rRNA

Answer 22

Ribosomal RNA

Along with ribosomal proteins, it makes up the ribosomes.

Question 23

What is snRNA?

Answer 23

Small nuclear RNA

Used to make things which process RNA (only in eukaryotes)

Question 24

What does ‘anti-parallel strands’ refer to?

Answer 24

How one strand is going in the forward direction (3’ -5’) and one in the opposite direction (5’ -3’)

Question 25

What is the nucleoplasm?

Answer 25

The cytoplasm of the nucleus. It serves as a suspension medium for all of the organelles inside the nucleus, and it also helps maintain the shape and structure of the nucleus.

Question 26

What happens during the transcription stage of protein synthesis?

Answer 26

1) DNA gyrase causes the double helix to unwind
2) DNA helicase unzips the DNA by breaking the hydrogen bonds
3) RNA polymerase catalyses the formation of hydrogen bonds between free RNA nucleotides with their complementary bases on the template strand
4) The formation of phosphodiester bonds creates an mRNA coding strand which passes out of the nucleus through the nuclear pore

Question 27

What happens during the translation stage of protein synthesis?

Answer 27

1) tRNA molecules with an amino acid binds to the mRNA strand with hydrogen bonds forming between the anitcodon and its complementary mRNA codon
2) the tRNA leaves the amino acid, which forms peptide bonds to the neighbouring amino acid
3) The order of amino acids in the polypeptide chain therefore depends on the sequence of codons in the mRNA.
4) The mRNA is then recycled and the newly synthesis polypeptide chain is folded into its shape in order to carry out its function

Question 28

What are the different parts of an amino acid?

Answer 28

The amine group: consists of a Nitrogen bonded to Two hydrogens (this is then bonded to the middle carbon)

Variable group: a variable that is attached to the middle carbon and is usually responsible for the nature of that amino acid

carboxyl group: (-COOH) contains a carbon double bonded to an oxygen and single bonded to an OH group.

Question 29

What is a proteins primary structure?

Answer 29

The sequence of amino acids in a protein chain.

Question 30

What is a proteins secondary structure?

Answer 30

The structure made when a polypeptide chain is folded into either a a-helix or a B-pleated sheet.

Question 31

What is a proteins tertiary structure?

Answer 31

The overall 3-D shape of the protein that is twisted through both a-helix and b-pleated sheets to allow maximum stability and lowest energy state.

Question 32

What is a proteins Quaternary structure.

Answer 32

The final structure of a protein molecule, containing more than one polypeptide chain.

Question 33

What bonds provide most of the interactions in protein folding?

Answer 33

Hydrogen bonds

Question 34

What are disulfide bridges?

Answer 34

Bonds which form between two cysteine proteins (cysteine proteins are a type of amino acid).

Question 35

What is a phosphodiester bond?

Answer 35

The bond between a sugar a phosphate group in a polynucleotide or dinucleotide.

Question 36

How does a phosphodiester bond join together two nucleotides to create a dinucleotide?

Answer 36

A condensation reaction occurs between the phosphate group and the sugar.

This involves the hydrogen being removed from the hydroxyl (OH) group on the carbon 3 of the ribose sugar. And the other hydroxyl group being removed from the phosphate group.

https://goo.gl/images/yixX71

This leaves a covalent (phosphodiester) bond between carbon 3 of the ribose sugar and the oxygen of the phosphate group.

H20 is left as a waste product.