Amino Acids and Proteins Overview

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Questions and Answers

What type of bond is responsible for holding together the secondary structure of proteins?

Covalent bonds

Peptide bonds

Hydrogen bonds (correct)

Ionic bonds

What is the role of enzymes in biological processes?

To change the temperature of the surroundings

To provide energy for reactions

To act as biological catalysts (correct)

To alter the pH of a reaction

Which structural form of proteins is characterized by being a single polypeptide chain?

Primary structure (correct)

Quaternary structure

Tertiary structure

Secondary structure

What is a disulfide bond in proteins?

A strong covalent bond between sulfur atoms Signup and view all the answers

What constitutes a nucleotide in DNA?

A sugar, a phosphate, and a base Signup and view all the answers

Which sugar is found in the nucleotides that make up DNA?

2-deoxyribose Signup and view all the answers

What characteristic makes enzymes stereospecific?

They interact with only one enantiomer Signup and view all the answers

What forms the sugar-phosphate backbone of a DNA molecule?

Sugar-phosphate bonds Signup and view all the answers

What defines an amino acid as an '𝛼-amino acid'?

Amine group on the second carbon Signup and view all the answers

Why do most amino acids exist as a single negative enantiomer in nature?

They fit into the correct cells within living organisms Signup and view all the answers

What occurs to amino acids under acidic conditions?

They produce a positive end Signup and view all the answers

What is the isoelectric point of an amino acid?

The pH at which it forms a zwitterion Signup and view all the answers

How are proteins formed?

By combining amino acids through dehydration synthesis Signup and view all the answers

What is the reaction of amino acids in basic conditions?

They lose hydrogen from the -OH group Signup and view all the answers

Which technique can be used to identify unknown amino acids?

Thin-layer chromatography Signup and view all the answers

What is formed when the overall pH of an amino acid is zero?

Zwitterion Signup and view all the answers

Which two bases bond with three hydrogen bonds?

Cytosine and Guanine Signup and view all the answers

What is the primary function of cisplatin as an anticancer drug?

To bond to mutated DNA strands Signup and view all the answers

Why is only the Z-isomer of cisplatin effective as a drug?

Cells in the natural world are chiral Signup and view all the answers

What type of bonding does cisplatin perform with DNA?

Ligand replacement Signup and view all the answers

What are the side effects of cisplatin when it bonds to heated DNA strands?

Hair loss Signup and view all the answers

In order for cisplatin to effectively prevent DNA replication, to which bases must it bond?

Two adjacent Guanine bases Signup and view all the answers

What is the structure of the effective isomer of cisplatin?

Square planar Signup and view all the answers

What aspect of cisplatin administration is important to mitigate side effects?

Administering in small amounts Signup and view all the answers

Study Notes

Amino Acids

An amino acid is a molecule with an amine group and a carboxylic acid group.
The amine group is always on the carbon in the chain which is a ‘2-amino acid’.
This is always the case and referred to as ‘𝛼-amino acids’.
The alpha carbon is often chiral with four different groups bonded to it - this means these amino acids exist as optical isomers.
Nearly all amino acids exist as a single negative enantiomer, meaning they ‘fit’ into the correct cells in living organisms.
Amino acids can react as both acids and bases depending on the conditions of the reaction.
When in acidic conditions, the amino acid becomes positively charged (acidic).
When in basic conditions, the amino acid becomes negatively charged (basic).
Zwitterions form when the pH of the molecule is zero, also called the isoelectric point.
Thin-layer chromatography can be used to identify unknown amino acids using UV light.

Proteins

Proteins are sequences of amino acids.
Amino acids are joined together by peptide links.
Boiling the protein in 6.0 moldm-3 HCl for 24 hours hydrolyses the protein.
Hydrolysis can also be carried out by enzymes in nature.
Complex structures include hydrogen bonds, van der Waals forces and sulfur-sulfur bonds.
Primary structure is a single polypeptide chain, often held together by hydrogen bonds.
Secondary structure forms either an alpha-helix or beta-pleated sheet.
Tertiary structure is a chain folded into a 3D coil with hydrogen and disulfide bonding.
Disulfide bridges are sulfur-sulfur bonds that keep the protein structure stable.

Enzymes

Enzymes are proteins with a tertiary structure that act as biological catalysts.
Enzymes contain active sites that are specific to the molecule they break down, called a substrate.
Enzymes are stereospecific, meaning they can only break down a single enantiomer and will have no effect on the other optical isomer.

DNA

DNA (deoxyribonucleic acid) is a condensation polymer made from sugar, a phosphate and a base.
These molecules join together to form a nucleotide, consisting of one of each molecule.
The sugar present in the nucleotide that makes DNA is 2-deoxyribose.
Multiple nucleotides are held together by sugar-phosphate bonds forming a polynucleotide strand.
The strand has a 'sugar-phosphate backbone'.
The four possible bases in DNA are:
- Adenine
- Cytosine
- Thymine
- Guanine
These bases pair up via hydrogen bonding to form a double helix structure of DNA.
Guanine and Cytosine are complementary bases that bond with three hydrogen bonds.
Thymine and Adenine are complementary bases that bond with two hydrogen bonds.

Anticancer Drugs

Cisplatin is used as an anticancer drug.
It is the cis isomer of a square planar complex of platinum.
Cells are chiral, meaning they are 3D, meaning only the Z-isomer of the drug is effective because it can fit into the cells correctly.
Cisplatin bonds to two adjacent Guanine bases.
Cancer cells replicate ‘bad DNA’.
Cisplatin bonds to these mutated DNA strands, preventing replication, by ligand replacement with guanine.
Cisplatin can sometimes bond to healthy DNA strands causing side effects such as hair loss.
The drug has to be administered in small amounts to try and reduce side effects.
Cisplatin remains an effective treatment for cancer, despite the side effects.

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Description

Explore the fascinating world of amino acids and their role in forming proteins. This quiz covers the structure, properties, and functions of amino acids, including their behavior under different conditions. Test your knowledge on zwitterions and the methods used to identify amino acids.