Biology Chapter on Proteins and Enzymes

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Questions and Answers

What term describes the basic building blocks of proteins?

Carbohydrates

Fatty acids

Nucleotides

Amino acids (correct)

Which property of amino acids contributes to the diversity of proteins?

Fixed structure

Limited chemical functionality

Uniform chirality

Polymerization capacity (correct)

Which of the following is a primary function of enzymes?

Serve as a structural component

Store genetic information

Act as biological catalysts (correct)

Transport oxygen in the blood

What role do antibodies play in the immune system?

Bind to antigens Signup and view all the answers

What type of proteins are responsible for transporting iron in the body?

Transport proteins Signup and view all the answers

In the absence of enzymes, what typically happens to biochemical reactions?

They can take significantly longer. Signup and view all the answers

How does the synthesis of transferrin in the body get regulated?

By the levels of iron Signup and view all the answers

Which characteristic is NOT related to the intrinsic properties of amino acids?

Presence of nucleic acids Signup and view all the answers

What characterizes the primary structure of a protein?

Amino acid sequence formed by peptide bonds Signup and view all the answers

Which of the following structures is described as involving hydrogen bonding between amide hydrogens and carbonyl oxygens?

Secondary structure Signup and view all the answers

What is the role of adrenocorticotropic hormone (ACTH) in the body?

Stimulates production of adrenal hormones Signup and view all the answers

What happens to proteins during denaturation?

The primary structure remains unchanged Signup and view all the answers

What is a defining feature of quaternary protein structure?

Spatial arrangement of multiple polypeptide chains Signup and view all the answers

How does myoglobin differ from hemoglobin?

Myoglobin functions to store oxygen, while hemoglobin transports it Signup and view all the answers

What is necessary to induce protein hydrolysis in a laboratory setting?

Acid or base, water, and heat Signup and view all the answers

What is the primary characteristic of secondary structure in proteins?

It is formed by hydrogen bonding between amide hydrogens and carbonyl oxygens. Signup and view all the answers

Which of the following statements about the α-helix is incorrect?

The helix is left-handed. Signup and view all the answers

What distinguishes the β-pleated sheet from other secondary structures?

It consists of chains that are nearly completely extended. Signup and view all the answers

In terms of tertiary structure, what primarily determines a protein's biological function?

Interactions among side chains or R groups. Signup and view all the answers

Which type of bond is described as the strongest among those maintaining tertiary structure?

Disulfide bridges Signup and view all the answers

What is characteristic of a fibrous protein's secondary structure?

It consists of fibers or sheets with one type of secondary structure. Signup and view all the answers

How do salt bridges contribute to protein structure?

They are ionic interactions between positively and negatively charged side chains. Signup and view all the answers

Which of the following best describes a characteristic of the β-pleated sheet structure?

All carbonyl O and amide H are involved in hydrogen bonding. Signup and view all the answers

What primarily causes the folding of the primary sequence of a polypeptide into a secondary structure?

Hydrogen bonding between amide and carbonyl groups. Signup and view all the answers

What role does transferrin play in iron transport within the body?

It binds and transports iron safely in the bloodstream. Signup and view all the answers

How does the release of iron from transferrin occur during transport?

Following a conformational change induced by decreased pH. Signup and view all the answers

Which proteins are specifically responsible for the transport and storage of oxygen in higher organisms?

Hemoglobin and myoglobin Signup and view all the answers

What is one of the main functions of regulatory proteins in the body?

Control metabolic and reproductive functions. Signup and view all the answers

Which statement describes the function of structural proteins?

They provide mechanical support in multicellular organisms. Signup and view all the answers

What characterized Recessive Dystrophic Epidermolysis Bullosa (EB)?

Severe chronic blistering from birth. Signup and view all the answers

Which proteins are part of the body's regulatory system to maintain homeostasis?

Insulin and glucagon Signup and view all the answers

What is the consequence of iron not being bound by specific carriers in the body?

It interacts dangerously with cellular structures. Signup and view all the answers

What initiates the transport of iron from transferrin into cells?

Internalization via receptor-mediated endocytosis. Signup and view all the answers

Which statement is true regarding keratin?

It provides structural support in hair and nails. Signup and view all the answers

At which pH does alanine have a net charge of 0?

pH 6.02 Signup and view all the answers

What is the primary function of electrophoresis in the analysis of amino acids?

To observe migration of amino acids based on their charge Signup and view all the answers

At a pH of 6.01, what will be the net charge of an amino acid with an isoelectric point of 2.77?

Net negative charge Signup and view all the answers

When subjected to electrophoresis at pH 6.01, which amino acid would not move from the center due to having a net charge of 0?

Alanine Signup and view all the answers

Which amino acid will migrate towards the positive electrode at pH 1?

Lysine Signup and view all the answers

What happens to the amino acid's charge as the pH increases above its pI?

The amino acid becomes negatively charged Signup and view all the answers

In electrophoresis, what role does ninhydrin serve?

To react with amino acids producing colored products Signup and view all the answers

Which amino acid would show a negative charge at pH 6.01?

Aspartic Acid Signup and view all the answers

Which pair correctly describes the pKa values and corresponding charges for glycine?

pKa 2.34: +1; pKa 9.60: 0 Signup and view all the answers

At what point will an amino acid display a net zero charge?

At its pI Signup and view all the answers

Study Notes

Chapter 3: Protein Structure and Function

This chapter examines protein structure and function, including amino acids, primary structures, secondary, tertiary, and quaternary structures, and factors influencing enzyme activity.

3.1 Proteins and Amino Acids

Proteins originate from the Greek word "proteios," signifying "first," highlighting their crucial roles in living organisms.
Proteins function as essential biological agents, with amino acids serving as their building blocks.
The remarkable diversity of proteins in nature arises from the intrinsic properties of only 20 common amino acids.
These properties include the capacity to polymerize, diverse acid-base properties, varied structures and chemical functionalities in side chains, and chirality (handedness in molecules). A chiral molecule cannot be superimposed on its mirror image.

3.2 Proteins: Primary Structure

The primary structure of a protein is defined by its linear sequence of amino acids.
Peptide bonds link adjacent amino acids, forming a polypeptide chain.

3.3 Proteins: Secondary, Tertiary, and Quaternary Structures

Secondary structure refers to the repeating, regular patterns formed by the polypeptide chain. Common examples of these patterns include alpha-helices and beta-pleated sheets. Hydrogen bonds between the amide hydrogens (N-H) and carbonyl oxygens (C=O) stabilize these structures.
Tertiary structure describes the three-dimensional arrangement of a polypeptide chain, resulting from interactions like hydrophobic interactions, hydrogen bonding, salt bridges (ionic interactions), and disulfide bridges.
Quaternary structure exists in proteins composed of more than one polypeptide chain. This structure describes how multiple polypeptide subunits or peptides (subunits) arrange to form a functional protein.

3.4 Enzymes

Enzymes are proteins that act as biological catalysts.
Enzymes speed up biochemical reactions that would otherwise take days or weeks to occur, or require extremely high temperatures.
The digestive enzymes pepsin, trypsin, and chymotrypsin, for example, break down dietary proteins into smaller, absorbable subunits.
Without enzymes, the body cannot effectively absorb nutrients.
Antibodies are proteins that play a crucial role in the body's immune response to fight off foreign invaders like bacteria and viruses.

3.5 Factors Affecting Enzyme Activity

Several factors can influence enzyme activity including temperature, pH value, and the presence of inhibitors or activators.
Various factors can influence protein structure and function, influencing their activity.

Classification of Some Proteins and Their Functions

Structural Proteins: Provide structural components, e.g., collagen, keratin,
Contractile Proteins: Enable muscle movement, e.g., myosin and actin;
Transport Proteins: Transport essential substances, e.g., hemoglobin, lipoproteins;
Storage Proteins: Store nutrients, e.g., casein, ferritin;
Hormonal Proteins: Regulate body metabolism, e.g., insulin, growth hormone;
Enzymes: Catalyze biochemical reactions, e.g., sucrase, trypsin;
Protective Proteins: Recognize and destroy foreign substances, e.g., immunoglobulins.

Amino Acids: A Deeper Dive

Amino acids have particular side chains (R-groups) that distinguish them and influence their properties including their polarity.
- Nonpolar: Hydrophobic;
- Polar neutral: Hydrophilic;
- Polar acidic: Hydrophilic and negatively charged;
- Polar basic: Hydrophilic and positively charged.
All amino acids are vital for normal tissue growth and development.
Essential Amino Acids: must be acquired through diet. They include:- PVT. TIM HALL – Phe, Val, Thr, Trp, Ile, Met, His, Arg, Leu, Lys
Non-essential amino acids can be produced by the body.
Chirality refers to a property of amino acids and their molecules where a molecule cannot be superimposed onto its mirror image.

Protein Functions (Detailed)

Movement Proteins: Essential to maintain movement, e.g., muscles, actin, and myosin.
Regulatory Proteins: Control diverse functions including cell metabolism and reproduction, like hormones such as insulin and glucagon.
Transport Proteins: Carry substances throughout the body like oxygen and iron. Hemoglobin, transferrin are examples of these.
Nutrient Storage Proteins: Supply amino acids for developing embryos and infants, e.g. egg albumin, casein.

Important Peptides and Protein Hormones

Various peptides and protein hormones are produced from different tissues in the body for various physiological functions.

Myoglobin and Hemoglobin

Myoglobin is an oxygen-storage protein, especially within muscle tissue.
Hemoglobin transports oxygen throughout the body in the blood.
Myoglobin has a higher affinity for oxygen than hemoglobin, allowing it to facilitate efficient oxygen transfer and uptake.
Each hemoglobin contains a heme group that can hold one oxygen molecule. The iron in the heme group binds oxygen.

Protein Denaturation

Denaturation disrupts the secondary, tertiary, and quaternary structures of proteins, causing them to lose their biological functions.
Physical and chemical factors like high temperature, pH extremes, and heavy metal ions cause denaturation.

Protein Hydrolysis

Hydrolysis is the process of splitting peptide chains into simpler compounds.
In a laboratory setting, protein hydrolysis uses acidic or basic solutions and heat to catalyze peptide bond breakage.
In the human body, enzymes like peptidases catalyze protein hydrolysis for digestion purposes

Protein Sequencing

Determining amino acid sequences involves hydrolysis, identifying the products, and assembling the sequences like a puzzle.
Methods of hydrolysis include acid hydrolysis, and enzymatic hydrolysis using proteases/ peptidases (exo/endopeptidases), including trypsin, chymotrypsin, and others.
Additional techniques, like chemical methods (Sanger's method, Edman degradation, hydrazine method) are used for determining the specific amino acid sequence.

Electrophoresis

Electrophoresis is a method used to separate proteins and other charged molecules based on the difference in their net charge under the influence of an electric field.

Quaternary Structure

Quaternary structure refers to how multiple polypeptide chains (subunits) arrange to form larger, functional protein molecules.
This arrangement is stabilized by various forces similar to those holding tertiary structures together.

Conjugated Proteins

Conjugated proteins are proteins with additional chemical components or prosthetic groups . These groups (e.g. carbohydrates, lipids, metals) attached help modify the proteins' structure and function.

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Test your understanding of proteins and enzymes with this quiz! You'll explore the fundamental concepts related to amino acids, protein structures, and the functions of enzymes and hormones in the body. Perfect for students looking to reinforce their knowledge in biology.