A-Level Chemistry (AQA) > 3.3.13 Amino acids, proteins, DNA > Flashcards

3.3.13 Amino acids, proteins, DNA Flashcards

Relate biological molecules to chemical structure by analysing bonding, interactions, and macromolecular organization. (61 cards)

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1
Q

What type of organic compound contains both an amine group and a carboxylic acid group?

A

Amino acid

Amino acids contain –NH₂ and –COOH functional groups.

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2
Q

Why do amino acids show both acidic and basic behaviour?

A

Two functional groups:

  • a basic amine group (–NH₂)
  • an acidic carboxyl group (–COOH)

This dual functionality allows amino acids to act as both acids and bases, contributing to their role in biological systems.

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3
Q

Fill in the blank:

A molecule containing both positive and negative charges is called a ______.

A

zwitterion

Amino acids commonly exist in this form in solution.

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4
Q

True or False:

In a zwitterion, the amino group is protonated and the carboxyl group is deprotonated.

A

True

The structure contains –NH₃⁺ and –COO⁻ groups.

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5
Q

What form does an amino acid mainly exist in at neutral pH?

A

Zwitterion

The molecule has both positive and negative charges but overall neutrality.

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6
Q

True or False:

In acidic solution, the carboxyl group of an amino acid exists as –COO⁻.

A

False

In acidic conditions it becomes –COOH.

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7
Q

Fill in the blank:

In acidic solution, the amino group of an amino acid exists as ______.

A

–NH₃⁺

The nitrogen atom becomes protonated.

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8
Q

What happens to the carboxyl group of an amino acid in alkaline solution?

A

Deprotonated

It exists as the carboxylate ion –COO⁻.

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9
Q

True or False:

In alkaline solution, the amino group of an amino acid exists mainly as –NH₂.

A

True

The proton is removed under basic conditions.

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10
Q

Fill in the blank:

In alkaline conditions, amino acids form ions containing ______ and –NH₂ groups.

A

–COO⁻

The molecule becomes negatively charged overall.

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11
Q

Why are amino acids described as amphoteric?

A

React with acids and bases

They can donate or accept protons.

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12
Q

What property allows amino acids to form zwitterions?

A

Internal proton transfer

The –COOH group donates H⁺ to the –NH₂ group.

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13
Q

What type of biological macromolecules are formed from amino acids joined together?

A

Proteins

Proteins are long chains of amino acids linked by peptide bonds.

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14
Q

What type of bond links amino acids together in proteins?

A

Peptide bond

A peptide bond forms between the –COOH of one amino acid and –NH₂ of another.

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15
Q

Fill in the blank:

The linkage formed between amino acids in proteins is called a ______ bond.

A

peptide

This bond forms through a condensation reaction.

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16
Q

True or False:

Formation of a peptide bond involves the removal of a molecule of water.

A

True

It is a condensation reaction between the carboxyl and amine groups.

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17
Q

What level of protein structure refers to the sequence of amino acids in the chain?

A

Primary structure

This is determined by the order of amino acids in the polypeptide.

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18
Q

True or False:

The α-helix and β-pleated sheet are examples of secondary protein structure.

A

True

These structures arise from hydrogen bonding in the backbone.

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19
Q

Fill in the blank:

Hydrogen bonding stabilises the ______ structure of proteins.

A

secondary

These bonds form between the C=O and N–H groups in the chain.

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20
Q

What type of bond can form between sulfur atoms in certain amino acids?

A

Disulfide bond

These S–S bonds help stabilise protein structure.

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21
Q

True or False:

Disulfide bonds help maintain the tertiary structure of proteins.

A

True

They form cross-links within the folded protein molecule.

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22
Q

Fill in the blank:

The three-dimensional folding of a protein molecule is called its ______ structure.

A

tertiary

This structure results from interactions between side chains.

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23
Q

What process breaks peptide bonds to release individual amino acids?

A

Hydrolysis

Water reacts with the peptide bond to split it.

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24
Q

What chromatographic technique is used to separate amino acids in the laboratory?

A

Thin-layer chromatography

Amino acids are identified using their Rf values.

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25
What type of **biological molecules** act as catalysts in living organisms?
Enzymes ## Footnote Enzymes speed up biochemical reactions without being used up.
26
What type of **macromolecules** are enzymes made from?
Proteins ## Footnote Their structure is formed from folded polypeptide chains.
27
# Fill in the blank: The **region** of an enzyme where the **substrate binds** is called the _\_\_\_\_\_ site.
active ## Footnote This site has a specific shape complementary to the substrate.
28
# True or False: Enzymes act as **biological catalysts**.
True ## Footnote They increase reaction rate by lowering activation energy.
29
What molecule binds to the **active site** of an enzyme during a reaction?
Substrate ## Footnote The substrate fits into the enzyme’s active site.
30
# True or False: Enzyme active sites are **stereospecific**.
True ## Footnote They can only bind molecules with the correct three-dimensional shape.
31
# Fill in the blank: Enzymes are able to recognise specific molecules due to the _\_\_\_\_\_ of the **active site**.
shape ## Footnote The active site is complementary to the substrate.
32
Why can an enzyme bind only one **enantiomer** of a molecule?
Enzyme's active site is **stereospecific**. ## Footnote Only one mirror-image form fits the active site correctly.
33
# True or False: Enzyme inhibitors work by blocking the **active site** of an enzyme.
True ## Footnote This prevents the substrate from binding.
34
# Fill in the blank: A drug that prevents **substrate binding** by occupying the active site acts as an enzyme _\_\_\_\_\_.
inhibitor ## Footnote It reduces or stops enzyme activity.
35
What concept describes the matching **shapes** of enzyme active sites and substrates?
Lock-and-key model ## Footnote The substrate fits precisely into the active site.
36
How can computers assist in **modern drug development** targeting enzymes?
Molecular modelling ## Footnote Computer simulations help design molecules that fit enzyme active sites.
37
What large **biological molecule** carries **genetic information** in living organisms?
DNA ## Footnote DNA stands for deoxyribonucleic acid.
38
What are the **repeating units** that make up **DNA** called?
Nucleotides ## Footnote DNA is a polymer formed from many nucleotide monomers.
39
# Fill in the blank: Each **nucleotide** contains a phosphate group, a pentose sugar and a _\_\_\_\_\_.
base ## Footnote The base can be adenine, thymine, cytosine or guanine.
40
# True or False: The sugar present in DNA nucleotides is **2-deoxyribose**.
True ## Footnote It is a five-carbon sugar lacking one oxygen atom compared with ribose.
41
What are the **four nitrogen-containing bases** found in DNA?
* Adenine * Cytosine * Guanine * Thymine ## Footnote These bases attach to the sugar component of the nucleotide.
42
# True or False: DNA consists of a **single long chain** of nucleotides only.
False ## Footnote DNA forms two complementary strands.
43
# Fill in the blank: The **backbone of a DNA** strand consists of alternating _\_\_\_\_\_ and sugar units.
phosphate ## Footnote These form the sugar–phosphate backbone of the molecule.
44
What **shape** is formed when two DNA strands wind around each other?
Double helix ## Footnote The two strands twist together in a helical structure.
45
# True or False: **Hydrogen bonds** hold the **two strands of DNA** together.
True ## Footnote These bonds form between complementary bases.
46
# Fill in the blank: Adenine pairs with _\_\_\_\_\_ in DNA.
thymine ## Footnote These bases are connected by hydrogen bonds.
47
Which base pairs with **guanine** in DNA?
Cytosine ## Footnote G–C pairs are also held together by hydrogen bonds.
48
Why are the two strands of DNA described as **complementary**?
Specific base pairing ## Footnote Each base forms hydrogen bonds with only one specific partner.
49
What **platinum(II) complex** is commonly used as an anticancer drug?
Cisplatin ## Footnote Cisplatin contains Pt(II) coordinated to two chloride and two ammonia ligands in a cis configuration.
50
How does cisplatin interfere with cancer cell **DNA**?
Ligand replacement with guanine ## Footnote Cisplatin forms covalent bonds between platinum and nitrogen atoms on guanine bases.
51
# Fill in the blanks: By binding to DNA, cisplatin prevents _\_\_\_\_\_ _\_\_\_\_\_ of cancer cells.
DNA replication ## Footnote Cross-links distort the DNA structure, stopping replication.
52
# True or False: Cisplatin forms bonds with **adenine** in DNA to inhibit replication.
False ## Footnote Cisplatin primarily binds to guanine nitrogen atoms.
53
What type of **chemical reaction** occurs between cisplatin and DNA?
Ligand substitution ## Footnote Chloride ligands are replaced by nitrogen atoms in DNA.
54
# True or False: The **cis configuration** of cisplatin is important for its activity.
True ## Footnote The cis arrangement allows cross-linking of adjacent guanine bases.
55
# Fill in the blank: Drugs like **cisplatin** can have adverse effects because they also affect _\_\_\_\_\_ cells.
healthy ## Footnote Rapidly dividing normal cells can be damaged, causing side effects.
56
Why must the benefits and risks of **cisplatin** be carefully assessed?
Balance of therapeutic effect vs toxicity. ## Footnote It can kill cancer cells but also harm normal cells.
57
# True or False: Cisplatin is selective only for **cancer cells** and does not affect normal cells.
False ## Footnote Some normal rapidly dividing cells are also affected.
58
# Fill in the blank: **Cisplatin** prevents DNA replication by forming covalent cross-links between _\_\_\_\_\_ bases on DNA.
guanine ## Footnote Cross-linking distorts the double helix and blocks replication.
59
What is the **primary target of cisplatin** inside a cell?
DNA ## Footnote Binding to guanine bases disrupts replication and transcription.
60
Why does **cisplatin** cause side effects such as nausea and kidney damage?
Non-specific toxicity ## Footnote Healthy cells that divide rapidly or process the drug can be affected.
61
How can you visualise **amino acids** on a **TLC plate**?
Spray with ninhydrin or view under UV light.
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