A-Level Biology (AQA) > 3.1.5 Nucleic Acids > Flashcards

3.1.5 Nucleic Acids Flashcards

Describe the structure of DNA and RNA and explain how nucleotide sequences store and transfer genetic information. (32 cards)

Study These Flashcards
1
Q

What type of biological molecule carries genetic information in almost all living cells?

A

DNA

Stores hereditary information and forms chromosomes in eukaryotic cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Which molecule carries genetic instructions from DNA to ribosomes during protein synthesis?

A

mRNA

Acts as an intermediary between DNA and ribosomes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What type of macromolecule are both DNA and RNA classified as?

A

Polynucleotides

They are long chains of repeating nucleotide monomers.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the monomer unit that builds both DNA and RNA polymers?

A

Nucleotide

Each nucleotide consists of a pentose sugar, phosphate group and nitrogen-containing base.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What three components make up a nucleotide?

A
  • Pentose sugar
  • Phosphate group
  • Nitrogen-containing base

These components form the basic unit of nucleic acids.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Which pentose sugar is present in DNA nucleotides?

A

Deoxyribose

Deoxyribose lacks one oxygen atom compared with ribose.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Which pentose sugar is present in RNA nucleotides?

A

Ribose

Ribose contains one more oxygen atom than deoxyribose.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Which four organic bases occur in DNA nucleotides?

A
  • Adenine
  • Cytosine
  • Guanine
  • Thymine

Often abbreviated as A, C, G and T.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Which organic base is found in RNA instead of thymine?

A

Uracil

RNA contains A, C, G and U.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What type of reaction joins two nucleotides together when forming a nucleic acid polymer?

A

Condensation reaction

Water is released during the formation of the bond.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the name of the covalent bond formed between nucleotides in DNA and RNA chains?

A

Phosphodiester bond

Forms between the phosphate group of one nucleotide and the sugar of another.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the overall three-dimensional shape of a DNA molecule?

A

Double helix

Two polynucleotide strands twist around each other.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What type of bond holds the two DNA strands together?

A

Hydrogen bonds

These occur between complementary bases.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How are bases paired between the two DNA strands?

A

Complementary base pairing

Adenine pairs with thymine and cytosine pairs with guanine.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

True or False:

DNA consists of two polynucleotide chains that twist to form a double helix.

A

True

The strands run in opposite directions and are joined by hydrogen bonds.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

True or False:

RNA usually forms a long double-stranded helix like DNA.

Study These Flashcards
A

False

RNA is usually a shorter single polynucleotide chain.

17
Q

What structure in cells is made partly from RNA and is responsible for protein synthesis?

Study These Flashcards
A

Ribosome

Ribosomes consist of ribosomal RNA (rRNA) and proteins.

18
Q

Fill in the blank:

A DNA molecule consists of two ______ chains held together by hydrogen bonds between bases.

Study These Flashcards
A

Polynucleotide

Each chain is made from many nucleotides joined by phosphodiester bonds.

19
Q

Why did early scientists doubt that DNA carried genetic information?

Study These Flashcards
A

DNA appeared too simple.

DNA has only four bases and a repeating structure, appearing too simple to encode complex information.

20
Q

If 30% of the bases in a DNA strand are adenine, what percentage must be thymine?

Study These Flashcards
A

30%

Complementary base pairing means A pairs with T in equal proportions.

21
Q

How does DNA replication ensure that genetic information is maintained when a cell divides?

Study These Flashcards
A

Semi-conservative replication

Each daughter DNA molecule contains one original strand and one newly synthesised strand.

22
Q

What type of structure must be unwound at the start of DNA replication?

Study These Flashcards
A

Double helix

The two antiparallel polynucleotide strands must separate so their bases can be copied.

23
Q

Which enzyme separates the two DNA strands during replication by breaking the bonds between bases?

Study These Flashcards
A

DNA helicase

This enzyme unwinds the helix and breaks hydrogen bonds between complementary bases.

24
Q

What type of bond between complementary bases must be broken to separate the DNA strands?

Study These Flashcards
A

Hydrogen bonds

These weak bonds hold base pairs together between the two strands.

25
During replication, exposed bases on the original strand attract free nucleotides according to which **rule** of **base pairing**?
Complementary base pairing ## Footnote Adenine pairs with thymine and cytosine pairs with guanine.
26
# Fill in the blank: Free DNA nucleotides align with bases on the original strand because it acts as a \_\_\_\_\_\_.
Template strand ## Footnote Each original strand guides the order of nucleotides in the new strand.
27
Which enzyme joins adjacent nucleotides together to build the **new DNA strand** during **DNA replication**?
DNA polymerase ## Footnote It catalyses the formation of phosphodiester bonds during strand synthesis.
28
What type of **reaction** joins neighbouring nucleotides together during **DNA replication**?
Condensation reaction ## Footnote A molecule of water is released when the sugar-phosphate backbone forms.
29
# True or False: Each **new DNA molecule** formed after replication contains **two completely new strands**.
False ## Footnote Each DNA molecule contains one original strand and one newly synthesised strand.
30
What process occurs when the **DNA strands separate** and the **helix opens** up during replication?
DNA unwinding ## Footnote This step allows the bases to become exposed for complementary pairing.
31
# Fill in the blank: The enzyme that builds the new strand forms bonds between nucleotides to create the **sugar-phosphate** \_\_\_\_\_\_.
Backbone ## Footnote The backbone consists of alternating deoxyribose sugars and phosphate groups.
32
Which classic experiment provided strong evidence supporting the **Watson–Crick model** of **DNA replication**?
Meselson–Stahl experiment
A-Level Biology (AQA)
flashcards
Decks in class (39)
# Cards
Brainscape helps you reach your goals faster, through stronger study habits.
© 2026 Bold Learning Solutions. Terms and Conditions