Proteins: Structure and Function

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Questions and Answers

Which type of protein is made up of more than 50 amino acids?

Dipeptides

Tripeptides

Peptides

Polypeptides (correct)

What is the primary role of proteins in cellular metabolism?

Transport of nutrients

Speed up chemical reactions (correct)

Regulate cellular signaling

Provide structural support

Which category of amino acids must be consumed in the diet?

Essential amino acids (correct)

Nonessential amino acids

Synthetic amino acids

Conditional amino acids

What is the first step in protein synthesis?

mRNA copy is made from DNA (A) Signup and view all the answers

How are amino acids characterized chemically?

Composed of carbon, hydrogen, oxygen, and nitrogen (A) Signup and view all the answers

Which type of protein is essential for intercellular signaling?

Signaling proteins (C) Signup and view all the answers

A polypeptide is best defined as a chain of:

More than 10 amino acids (B) Signup and view all the answers

What occurs after the mRNA attaches to the ribosome during protein synthesis?

tRNA is activated with complementary amino acids (C) Signup and view all the answers

What is the main structural function of microtubules in animal cells?

To provide a framework that resists compression (A) Signup and view all the answers

What are centrioles primarily composed of?

Nine triplets of microtubules (B) Signup and view all the answers

What type of tension do intermediate filaments specifically resist?

Tension (D) Signup and view all the answers

What role does tRNA play in protein synthesis?

It bonds with mRNA through its anticodon. (A) Signup and view all the answers

How are actin filaments arranged in muscle cells?

Parallel to one another (D) Signup and view all the answers

Which statement best describes fibrous proteins?

They are linked by disulphide bridges and have a rope-like structure. (C) Signup and view all the answers

Which protein is primarily involved in muscle contraction by interacting with actin?

Myosin (D) Signup and view all the answers

What triggers muscle fatigue according to the content provided?

Failure in excitation-contraction coupling (D) Signup and view all the answers

What defines a protein domain?

The basic structural unit of a protein that can fold independently. (A) Signup and view all the answers

What do antibodies primarily do?

Defend the body against antigens. (C) Signup and view all the answers

Which of the following elements is NOT typically found in proteins?

Phosphorus (A) Signup and view all the answers

What characteristic distinguishes microfilaments in terms of size compared to other cytoskeletal fibers?

They are the thinnest class of cytoskeletal fibers (A) Signup and view all the answers

Which of the following is a key characteristic of globular proteins?

They are folded roughly into a spherical shape. (A) Signup and view all the answers

What is a conjugated protein?

A protein associated with non-protein chemical groups. (A) Signup and view all the answers

What is the primary function of hemoglobin?

To transport oxygen in the blood. (C) Signup and view all the answers

What role do cilia serve in the respiratory system?

To sweep mucus and trapped debris from the lungs (B) Signup and view all the answers

What most likely precedes physiological fatigue in muscles?

Central fatigue (B) Signup and view all the answers

Which condition is characterized by the absence of the protein dystrophin?

Duchenne muscular dystrophy (B) Signup and view all the answers

What happens to muscle fibers during prolonged immobilization?

They diminish in size resulting in atrophy (B) Signup and view all the answers

What is a potential cause of motor protein defects like dynein deficiencies?

Chronic respiratory infections (D) Signup and view all the answers

Which disease is considered an amyloid disease affecting protein function?

Alzheimer's disease (C) Signup and view all the answers

What does the accumulation of misfolded proteins commonly lead to?

Neurodegenerative diseases (B) Signup and view all the answers

Which of the following is NOT a type of fiber found in the cytoskeleton?

Choline filaments (A) Signup and view all the answers

What is a likely outcome of prolonged muscle disuse?

Muscle atrophy (C) Signup and view all the answers

What is the significance of disulfide bonds in protein structure?

They create cross-linkages that stabilize protein conformation. (C) Signup and view all the answers

How do proteins achieve their unique functions?

Through conformation, which is determined by the arrangement of amino acids. (D) Signup and view all the answers

What role do prosthetic groups play in proteins?

They contribute to the protein's functional activity when non-protein molecules are required. (B) Signup and view all the answers

What is feedback inhibition in enzymatic pathways?

Regulation of enzyme activity by the end product of the pathway. (D) Signup and view all the answers

What is allosteric regulation?

It requires a change in protein conformation due to binding at a second site. (B) Signup and view all the answers

Which of the following statements about ligands is true?

Ligands have the potential to regulate protein activity through binding. (D) Signup and view all the answers

How does positive feedback differ from negative feedback in enzymatic pathways?

Positive feedback stimulates enzyme activity while negative feedback slows it down. (D) Signup and view all the answers

What is the role of amino acid sequences in the folding of proteins?

They determine the arrangement of amino acids necessary for the formation of binding sites. (C) Signup and view all the answers

Study Notes

What are Proteins?

Proteins are chains of amino acids, they are fundamental in almost everything an organism does.

Structure of Proteins

Peptides contain fewer than 50 amino acids.
- Dipeptides have 2 amino acids.
- Tripeptides have 3 amino acids.
- Polypeptides have more than 10 amino acids.
Proteins contain more than 50 amino acids.
Typical protein chains have between 100 and 10,000 amino acids linked together.
Amino acids are composed of carbon, hydrogen, oxygen, and nitrogen.

Essential, Nonessential, and Conditional Amino Acids

Essential amino acids must be consumed in the diet.
Nonessential amino acids can be synthesized by the body.
Conditional amino acids cannot be synthesized due to illness or lack of necessary precursors.

Protein Synthesis

mRNA copy is made of one of the DNA strands.
mRNA copy moves out of the nucleus into the cytoplasm.
tRNA molecules are activated as their complementary amino acids are attached to them.
mRNA copy attaches to the small subunit of the ribosomes in the cytoplasm.
A tRNA bonds complementarily with the mRNA via its anticodon.
The ribosome moves along. The first tRNA leaves the ribosome.
The process is repeated with 2nd and 3rd tRNA.
Eventually, a stop codon is reached on the mRNA. The newly synthesized polypeptide leaves the ribosome.

Elements in a Protein

Carbon, hydrogen, oxygen, nitrogen, and sulfur.

Protein Secretion

Golgi bodies are numerous and active in secretory cells.
Example secretory cells include gastric gland cells in stomach walls, pancreas.
Proteins secreted by secretory cells include mucus, and insulin

Proteins & Their Function

Proteins make up about 15% of the cell.
Proteins in the cell have various functions.
- Enzymes regulate metabolism.
- Structural proteins provide support.
- Transport proteins help with movement and transport.
- Motor proteins are responsible for movement.
- Storage proteins store important nutrients.
- Signaling proteins carry signals between cells.
- Receptor proteins receive signals.
- Gene regulation proteins control gene expression.
- Special function proteins have unique roles.

Fibrous Proteins & Globular Proteins

Fibrous proteins are several spiral-shaped polypeptide molecules linked in parallel by disulfide bridges.
Globular proteins are several polypeptide chains folded roughly into a spherical shape.

Protein Domains

A domain is a basic structural unit in a protein’s structure that can fold into a stable structure independently.
Proteins can have one or many domains depending on their size.

Hemoglobin

Hemoglobin is a conjugated protein.
Hemoglobin has a globular protein called globin and a non-protein containing iron called heme.
Hemoglobin has 2 alpha globin subunits and 2 beta globin subunits.

Protein Assemblies

Proteins can form large assemblies.
Proteins can form long chains if they have two binding sites.
Actin fibers in muscles and the cytoskeleton are made from thousands of actin molecules.
Cross-linkages can be between two parts of a protein or between two subunits.
Disulfide bonds (S-S) form between adjacent -SH groups on the amino acid cysteine.

Protein Interactions

The conformation of a protein gives it a unique function.
Proteins interact with other molecules, usually one or a few molecules.
Ligand is the molecule that a protein can bind to.
The binding site is the part of the protein that interacts with the ligand.

Prosthetic Groups

Prosthetic groups can enhance protein performance.
Hemoglobin requires heme to carry oxygen.
A prosthetic group required by an enzyme is called a co-enzyme.
Co-enzymes help catalyze chemical reactions.

Regulation of Enzymes

Feedback inhibition occurs when the end product of a metabolic pathway regulates the enzyme early in the pathway.
Negative feedback is when the accumulation of the final product inhibits the pathway.
Positive feedback occurs when a regulatory molecule stimulates the activity of the enzyme.
Allostery is the conformational coupling of two widely separated binding sites where the active site recognizes the substrate, and the second site recognizes the regulatory molecule.
An allosteric protein is a protein regulated by allostery.
Allosteric regulation causes proteins to change their conformation after ligand binding.

Cytoskeleton and Motor Proteins

Microtubules are hollow tubes made of tubulin protein in the cytoplasm of eukaryotic cells involved in the movement of organelles.
Intermediate filaments are fibrous proteins that provide structural support for the cell.
Microfilaments are made of actin protein and are involved in cell movement and shape.
Microtubules resist compression, provide tracks for organelle movement, and play a role in cell division.
Intermediate filaments are more permanent than microtubules or microfilaments and reinforce cell shape and fix organelle location.
Microfilaments are involved in cell movement, cell division, and provide structural support.

Muscle Structure and Contraction

Muscles use a sliding filament mechanism.
Actin filaments and myosin filaments interact to cause muscle contraction.
Calcium ions trigger the release of the myosin head binding sites on actin allowing the muscle to contract.
The power stroke is the process of myosin heads pulling actin filaments closer together, causing the muscle to shorten.
Cross-bridge cycling is the continuous process of myosin heads binding to and releasing from actin filaments, generating muscle contraction.

Muscle Fatigue

Muscle fatigue occurs when the muscle can no longer generate or sustain the expected power output.
It is thought to be caused by failure in excitation-contraction coupling within the muscle.
Acidosis from lactic acid buildup may contribute to the sensation of fatigue perceived in the brain.

Muscle Disorders

Muscle overuse can lead to fatigue and tears in the muscle tissue.
Muscle disuse can lead to atrophy.
Acquired disorders can be caused by infections, toxins, or injuries.
Inherited disorders, such as muscular dystrophy, are often difficult to treat.

Duchenne Muscular Dystrophy

Duchenne muscular dystrophy is caused by the absence of the cytoskeletal protein dystrophin.
This leads to muscle fiber tears, calcium influx, and breakdown of muscle components.

Diseases Associated with Motor Protein Defects

Dynein deficiencies can lead to respiratory tract infections due to cilia dysfunction.
Defects in muscular myosin can cause myopathies and damaged muscle tissue.

Misfolded Proteins and Neurodegenerative Diseases

Misfolded proteins can accumulate and cause disease.
Amyloid diseases, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease are caused by misfolded proteins.

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Description

This quiz explores the fundamental concepts of proteins, including their structure, types of amino acids, and the process of protein synthesis. It covers essential, nonessential, and conditional amino acids while detailing the intricacies of protein formation. Test your knowledge of these vital biological molecules!