3.1.5 Nucleic Acids are Important Information-Carrying Molecules

Question 1

(Nucleic acids) Why are DNA and RNA examples of polymers? (3)

Answer 1

DNA and RNA are large polymers.
They are made from small, soluble, repeating units called nucleotides (DNA or RNA nucleotides).
MANY nucleotides can be linked together to form the much larger polymers.

Question 2

(Nucleic acids) Detail the structural features of DNA. (7)

Answer 2

Polynucleotide (polymer) made from many DNA nucleotides (monomers).
Double stranded helix.
Anti-parallel strands.

Complementary base pairing between strands / nitrogenous bases.
Via hydrogen bonding.
A-T, C-G

Nucleotides are linked via strong, phosphodiester bonds forming a “sugar-phosphate” backbone.

Question 3

(Nucleic acids) What are DNA molecules / chromosomes like in eukaryotic (nucleated) cells?

Answer 3

Linear, coiled and associated with histones.

Question 4

(Nucleic acids) What is the function of DNA?

Answer 4

DNA molecules hold genetic information.

Question 5

(Nucleic acids) Go into further depth of how DNA molecules hold genetic information. (4)

Answer 5

1) Hereditary information can be passed to the next generation
2) Genes hold instructions for synthesising proteins.
3) Complementary base pairing between strands allows for DNA replication / transcription of genes.
4) Both strands can be separated for acting as templates for DNA replication and also transcription.

Question 6

(Nucleic acids) Explain the stability of DNA. (3)

Answer 6

The stable structure means mutations (changes to the genetic code) are rare.

Phosphodiester bonds protect the more chemically reactive nitrogenous bases inside the double helix.
Hydrogen bonding links the 2 complementary strands together.

Question 7

(Nucleic acids) Why were scientists originally doubtful DNA carried the “genetic code”?

Answer 7

DNA is only made from 4 nucleotides. There are only 4 nitrogenous bases. A,T, C and G.

Whereas there are many different proteins!

Question 8

(Nucleic acids) Detail semi-conservative replication. (11)

Answer 8

DNA helicase unwinds the DNA helix.
Breaks (not hydrolyses!) the hydrogen bonds.
Separates the 2 strands.
Both strands act as a template for forming new strands.

Free, activated DNA nucleotides complementary base pair via hydrogen bonding.
A-T, T-A, C-G, G-C
DNA polymerase forms phosphodiester bonds between the nucleotide monomers.
Condensation reaction, using ATP, water released.

Nucleotide monomers are always added onto the 3’ end of a lengthening new strand.

Creates 2 identical DNA molecules, identical to the original DNA molecule.

Each new DNA molecule consists of one strand from the original double helix and one newly synthesised strand.

Question 9

(Nucleic acids) Why can nucleotides (monomers) only be attached to the 3-prime end of a polynucleotide?

Answer 9

DNA nucleotides (monomers) are only added to the 3’ end of a lengthening strand.

The phosphate group attached to C5 on the nucleotide reacts with the hydroxyl group on C3 of the last nucleotide in the chain.

Because… the DNA polymerase is an enzyme with a specifically shaped active site.

Question 10

(Nucleic acids) Compare DNA and RNA: Characteristic: Pentose sugar

Answer 10

DNA: deoxyribose
RNA: ribose

Question 11

(Nucleic acids) Compare DNA and RNA: Characteristic: Nitrogenous bases

Answer 11

DNA: A, T, C, G
RNA: A, U, C, G

Question 12

(Nucleic acids) Compare DNA and RNA: Characteristic: Length

Answer 12

DNA: very long
RNA: relatively short

Question 13

(Nucleic acids) Compare DNA and RNA: Characteristic: Shape

Answer 13

DNA: linear, double helix, coiled
RNA: mRNA (linear single strand), rRNA (bulky, with proteins), tRNA (bulky, t-shaped)

Question 14

(Nucleic acids) Compare DNA and RNA: Characteristic: Cell location

Answer 14

DNA: nucleus
RNA: mRNA in nucleus and cytoplasm, rRNA in cytoplasm attached to RER, tRNA in cytoplasm attaching to amino acids

Question 15

(Nucleic acids) Compare DNA and RNA: Characteristic: Lifespan

Answer 15

DNA: long and stable
RNA: short, often broken down

Question 16

(Nucleic acids) Compare DNA and RNA: Characteristic: Role

Answer 16

DNA: Storage of genetic information/code for building proteins
RNA: Protein synthesis

Question 17

(Nucleic acids) What does mRNA correspond to?

Answer 17

Linear, single strands

Question 18

(Nucleic acids) What does rRNA correspond to?

Answer 18

Bulky, with proteins

Question 19

(Nucleic acids) What does tRNA correspond to?

Answer 19

Bulky, t-shaped

Question 20

(Nucleic acids) What are ribosomes formed from?

Answer 20

RNA and proteins.

Question 21

(Nucleic acids) What does a condensation reaction between two nucleotides form?

Answer 21

A phosphodiester bond.

Question 22

(Nucleic acids) State the components of a DNA nucleotide.

Answer 22

Deoxyribose, a phosphate group and one of the organic bases: adenine, cytosine, guanine or thymine.

Question 23

(Nucleic acids) State the components of a RNA nucleotide.

Answer 23

Ribose, a phosphate group and one of the organic bases: adenine, cytosine, guanine or uracil.

Question 24

(Nucleic acids) What is each nucleotide formed from?

Answer 24

A pentose, a nitrogen-containing organic base and a phosphate group.

Question 25

(Nucleic acids) What does ‘DNA’ stand for?

Answer 25

Deoxyribonucleic acid.

Question 26

(Nucleic acids) What does ‘RNA’ stand for?

Answer 26

Ribonucleic acid.

Question 27

(Nucleic acids) What is DNA and RNA?

Answer 27

Important information-carrying molecules.

Question 28

(Nucleic acids) What is the function of RNA?

Answer 28

To transfer genetic information from DNA to the ribosomes.

Question 29

(Nucleic acids) What does semi-conservative replication of DNA ensure?

Answer 29

Genetic continuity between generations of cells.