Biochemistry: Amino Acids and Proteins

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Questions and Answers

Which type of protein is primarily responsible for the movement of muscles?

Hormonal proteins

Defensive proteins

Contractile and motor proteins (correct)

Transport proteins

What is the role of insulin in vertebrates?

Facilitate nerve impulse transmission

Transport oxygen in the blood

Regulate blood sugar concentration (correct)

Combat bacteria and viruses

How many standard amino acids are used by cells to build proteins?

20 (correct)

Which protein is responsible for transporting oxygen in vertebrate blood?

Hemoglobin Signup and view all the answers

What type of protein acts as receptors built into the membrane of a nerve cell?

Receptor proteins Signup and view all the answers

Which of the following amino acids are considered non-standard due to their recent discovery?

Selenocysteine and Pyrrolysine Signup and view all the answers

What is a primary function of antibodies in the immune system?

Combat bacteria and viruses Signup and view all the answers

Which physiological process is glutamate most directly associated with?

Nerve impulse transmission Signup and view all the answers

What is the primary structure of proteins made up of?

A sequence of amino acids Signup and view all the answers

Which type of protein is primarily responsible for accelerating chemical reactions?

Enzymatic proteins Signup and view all the answers

How are amino acids linked to form proteins?

Through peptide bonds Signup and view all the answers

What role do storage proteins serve?

Storing amino acids and small molecules Signup and view all the answers

Which of the following proteins provides fibrous support in connective tissues?

Collagen Signup and view all the answers

What characteristic defines each protein's specific function within an organism?

The protein's three-dimensional structure Signup and view all the answers

What percentage of the dry mass of cells do proteins account for?

More than 50% Signup and view all the answers

Which protein type is not classified as structural or enzymatic?

Transport proteins Signup and view all the answers

What effect does denaturation have on proteins?

It changes them into a less ordered form, losing their function. Signup and view all the answers

Which factor is NOT mentioned as a cause of protein denaturation?

Exposure to radioactive materials. Signup and view all the answers

What is a consequence of nonenzymatic modification of amino acids?

Loss of function in proteins. Signup and view all the answers

Globular proteins are characterized by which type of structure?

Spherical tertiary or quaternary structure. Signup and view all the answers

What effect does a low pH have on proteins?

Disrupts ionic and hydrogen bonds formed by carboxylate groups. Signup and view all the answers

Which of the following statements about hemoglobin is true?

HbA1c is a modification that decreases its oxygen delivery ability. Signup and view all the answers

High concentrations of which type of substances can cause denaturation?

Both polar and non-polar substances. Signup and view all the answers

How does temperature affect protein structure?

It increases the vibrational energy of atoms. Signup and view all the answers

Which amino acids are categorized as having acidic side chains?

Amino acids that release protons at physiological pH Signup and view all the answers

What distinguishes basic amino acids from acidic amino acids in terms of their R groups?

Basic amino acids have R groups that accept protons and are positively charged Signup and view all the answers

At physiological pH, how is histidine typically characterized in terms of its charge?

Weakly basic and neutral Signup and view all the answers

Which of the following statements is true regarding chiral amino acids?

Amino acids with chiral α-carbons have D and L isomeric forms Signup and view all the answers

Which property allows amino acids to act as buffers in solution?

Their carboxyl and amino groups can donate or accept protons Signup and view all the answers

Which characteristic is common to polar amino acids with uncharged side chains?

They possess functional groups that can form hydrogen bonds with water Signup and view all the answers

What is the net charge of amino acids with neutral side chains at physiological pH?

Zero net charge Signup and view all the answers

Which of the following is a distinctive feature of amino acids with polar charged side chains?

They carry positive or negative charges at physiological pH Signup and view all the answers

What primarily determines the sequence of amino acids in a polypeptide?

Inherited genetic information Signup and view all the answers

Which of the following describes the rigidity of peptide bonds?

Peptide bonds have a partial double bond character. Signup and view all the answers

What is the main characteristic of proteins at the tertiary structural level?

They have a three-dimensional structure reflecting the arrangement of all amino acids. Signup and view all the answers

Which of the following accurately describes the primary structure of a protein?

It is the unique sequence of amino acids in a polypeptide. Signup and view all the answers

At which structural level do hydrogen bonds stabilize the polypeptide chain?

Secondary structure Signup and view all the answers

What distinguishes the quaternary structure of a protein from its other structures?

It consists of two or more polypeptide chains interacting together. Signup and view all the answers

What determines the three-dimensional structure of a protein?

The unique sequence of its amino acids Signup and view all the answers

What is a key feature of polypeptide chains adjacent to peptide bonds?

They can rotate freely around their bonds. Signup and view all the answers

Study Notes

General Properties of Amino Acids

Composed of 20 standard amino acids, which are monomeric units of proteins, encoded by DNA.
Non-standard amino acids can arise from modification of standard amino acids (e.g., hydroxyproline).
Exhibit properties relevant to their side chains, influencing their roles in proteins.

Protein Overview

Proteins account for over 50% of the dry mass in cells and perform diverse functions.
Composed of polypeptides, which are linear chains of amino acids folded into a specific three-dimensional structure.
Human cells contain tens of thousands of different proteins with distinct structures and functions.

Functions of Proteins

Enzymatic: Catalyze chemical reactions (e.g., digestive enzymes).
Structural: Provide support (e.g., collagen, keratin).
Storage: Store amino acids and small molecules (e.g., ovalbumin, casein).
Transport: Move substances across membranes (e.g., hemoglobin).
Hormonal: Regulate activities in the body (e.g., insulin).
Receptor: Respond to chemical signals (e.g., nerve cell receptors).
Contractile and Motor: Facilitate movement (e.g., actin, myosin).
Defensive: Protect against disease (e.g., antibodies).

Classification of Amino Acids

Polar, Uncharged: Contain hydrophilic side chains, typically found on the surface of globular proteins.
Polar, Charged: Include acidic (negative charge) and basic (positive charge) amino acids.
Acidic Side Chains: Proton donors, remain ionized at physiological pH (e.g., aspartate, glutamate).
Basic Side Chains: Proton acceptors, positively charged at physiological pH (e.g., lysine, arginine).

Isomerism in Amino Acids

Most amino acids (except glycine) have chiral α-carbons, leading to L and D configurations.
Only L isomers are found in mammalian proteins.

Acid-Base Properties

Amino acids can act as buffers due to their carboxyl and amino groups, which can donate or accept protons depending on the pH.

Peptide Bonds

Peptide bonds have partial double bond character, preventing rotation around the C-N axis, but adjacent bonds can rotate freely.

Protein Structure

Proteins have four structural levels:
- Primary: Unique sequence of amino acids.
- Secondary: Coils and folds stabilized by hydrogen bonds.
- Tertiary: Overall 3D configuration determined by various interactions.
- Quaternary: Assembly of multiple polypeptides.

Denaturation of Proteins

Caused by environmental changes (e.g., temperature, pH, high substance concentrations).
Denatured proteins lose their native shape and biological activity.

Nonenzymatic Modifications

Post-translational modifications (e.g., glycosylation) can alter protein function.
Glycosylated hemoglobin (HbA1c) example: affects oxygen affinity and delivery.

Classification of Proteins by Structure

Globular Proteins: Spherical in shape and involved in various functions.
Fibrous Proteins: Typically elongated and provide structural support.

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Description

This quiz covers the general properties of amino acids and their role as building blocks of proteins. You'll also explore the diverse functions of proteins including their enzymatic, structural, storage, transport, and hormonal roles. Test your knowledge on the essential components and functions of proteins in biological systems.