BIOL 200 - Unit 3 - Proteins and Enzymes
An allosteric ______ binds to a site in the enzyme other than the active site and by doing so it keeps the enzyme in its active configuration.
activator
Proteins are made of one or more unbranched chains of _____ _____.
amino, acids
Which of the following statements about the relationship between enzymes and environmental conditions are true?
- Changing environmental conditions may alter the structure of enzymes - The optimum conditions for enzyme activity are usually similar to the conditions where the enzyme normally functions. -Changing environmental conditions may alter the activity of enzymes.
The ways in which multienzyme complexes improve catalytic efficiency.
-Because products do not leave the complex, there are no unwanted side reactions. -The product of one reaction can be delivered to the next enzyme more easily. -All of the reactions inside the complex can be controlled as one unit.
What is(are) the effect(s) of a molecule binding to an allosteric site on an enzyme?
-Binding of a molecule to an allosteric site can inhibit the proper functioning of an enzyme. -Binding of a molecule to an allosteric site can enhance the proper functioning of an enzyme.
Which of the following interactions help determine a protein's tertiary structure?
-Disulfide bridges -Hydrophobic exclusion -Ionic bonds -Hydrogen bonds
What's true about cellular enzymes?
-Each enzyme in a cell catalyzes one or a few specific reactions. -Each cell has thousands of enzymes.
Characteristics of enzymes:
-Enzymes aren't changed or consumed in reactions -Enzymes lower the activation energy required for new bonds to form in a chemical reaction -Enzymes may be used more than once in a cell
Most enzymes in the human body work best at neutral pH. What are the reasons why changing the pH of the fluid in which a human enzyme is dissolved (for example to a pH of 3) will affect the enzyme's ability to function.
-Enzymes cannot maintain their three-dimensional shape at extreme pHs, such as a pH of 3. -The balance between positively and negatively charged amino acids in the enzyme is shifted.
What are the functions of proteins in living cells?
-Help the body recognize and destroy foreign microbes and cancer cells -Transport oxygen in the blood of vertebrates -Catalyze chemical reactions -PLay a key role in moving materials within cells
Statements about the effect of temperature on an uncatalzyed chemical reaction.
-Increased temperature increases random molecular movements which increases stress on bonds. -Increased temperature increases the rate of the reaction.
Statements that accurately describe multienzyme complexes
-Multienzyme complexes improve catalytic efficiency. -Enzymes in multienzyme complexes catalyze a sequence of reactions. -Within the multienzyme complex, products of one reaction can be delivered to the next reaction.
Select amino acids that are most likely to be found in the interior of a protein.
-Phenylalanine -Valine -Leucine
What are the three major structural components of an amino acid?
-Side chain (R) -Amino group -Carboxyl group
Statements that accurately describe cellular enzymes:
-Some cellular enzymes are found inside of cellular organelles. -Not all cellular enzymes are located in the cytoplasm. -Different enzymes can come together to form complexes.
Protein denaturation may be caused by an increase in which of the following?
-Temperature -ph -Ionic concentration
Statements about allosteric sites on enzymes.
-The binding of a substance to the allosteric site can switch an enzyme between its active and inactive configurations. -This is where a non-competitive inhibitor would bind.
statements about noncompetitive inhibitors:
-They bind to a site other than the active site of the enzyme -They cause the enzyme to change shape -They prevent the substrate from binding to the enzyme
Which of the following are functions of proteins?
-They catalyze chemical reactions -They provide structural support for many animal tissues -They play a key role in the contraction of muscles
How many polypeptides are present in a protein whose highest level of structure is tertiary structure?
1 polypeptide only
Although many different amino acids occur in nature, only _____ (number) L-amino acids commonly occur in protiens.
20
Proteins are polymers made up of how many different amino acids?
20
What is the optimal pH range for most human enzymes?
6-8
Which of the following accurately describes the chemical structure of a typical amino acid found in a protein?
A central carbon atom is bound to an amino group, carboxyl group, a side chain, and a hydrogen atom.
What best describes an allosteric inhibitor?
A molecule that binds to a site other than the active site of an enzyme and inhibits the enzyme's function.
What is a substrate?
A reactant molecule that binds to the active site of an enzyme
Where does a substrate bind on an enzyme in order for a chemical reaction to take place?
Active site
The ______ site is a specific region of an enzyme to which non-competitive inhibitors bind in order to regulate enzyme activity.
Allosteric
A substance that binds to an enzyme in a way which results in a decrease of enzyme activity is called a(n) ______.
Allosteric inhibitor
A molecule that binds to a site on the enzyme other than the active site and inhibits the enzyme's activity is called a(n) ______ inhibitor.
Allosteric, non-competitive
Each kind of protein has a unique sequence of ______ ______.
Amino acids
What are the building blocks of proteins?
Amino acids
What are the two major functional groups found in an amino acid, which allow it to form a peptide with another acid?
Amino group and carboxyl group
What is the best description of the fit between an enzyme and its substrate?
As the substrate binds to the enzyme, the shape of the active site changes to accommodate the reaction.
Where are the peptide bonds located in a polypeptide?
Between the amino group of one amino acid and the carboxyl group of another.
When two amino acids are linked together, a peptide bond is formed between the ______ group of one and the ______ group of another.
Carboxyl and amino
What are the two major functional groups found in an amino acid, which allow it to form a peptide bond with another amino acid?
Carboxyl group and amino group
How do cells regulate the activity of enzymes?
Cells can regulate the activity of enzymes by inhibiting or activating them.
______ are small organic molecules that temporarily attach to an enzyme and promote a chemical reaction without being changed during the reaction.
Coenzyme
What term refers to small chemicals, usually inorganic ions, that temporarily attach to the surface of an enzyme and promote a chemical reaction?
Cofactors
______ are small chemical components, usually inorganic ions, such as Zn2+, Cu2+, and Mn2+, that are often found in the active site of an enzyme, participating directly in catalysis.
Cofactors
_____ inhibitors bind to the active site of an enzyme and prevent the substrate from binding.
Competitive
What are competitive inhibitors?
Competitive inhibitors bind to the active site of an enzyme and prevent substrates from binding.
A protein with quaternary structure ______.
Contains two or more polypeptide chains
What type of reaction is responsible for linking amino acids together to form polypeptides?
Dehydration synthesis
Changes in a protein's environment can cause the protein to unfold and lose its shape in a process called which of the following?
Denaturation
If the four subunits that make up a hemoglobin molecule separate into four individual molecules without denaturation of the folded globin proteins, the process is called _____
Dissociation
Which of the following is observed when individual subunits making up a protein with quaternary structure separate without losing their tertiary structures?
Dissociation
Which type of interaction involves the formation of a covalent bond between two different amino acid side chains?
Disulfide bridge.
Which of the following best describes the relationship between temperature and enzyme activity?
Each enzyme has an optimum temperature where it functions best.
When a reactant binds to the active site of an enzyme, a(n) ______-_____ complex forms.
Enzyme-substrate
What is produced by the binding of enzyme and substrate?
Enzyme-substrate complex
______ are proteins or RNA molecules that act as catalysts to speed up reactions in living organisms.
Enzymes
Pepsin is an enzyme found in the stomach that functions best at an acidic pH. Why does pepsin not function well at a pH of 7?
Enzymes are sensitive to pH and function best across a narrow range of pH.
True or false: All of the enzymes that a cell has are found in the cells' cytoplasm.
False
True or false: Protein structure is usually not affected by changes in the temperature, pH, or ionic concentration of the surrounding solution.
False
Examples of protein motifs:
Helix - turn - helix β-barrel 2 β-pleated sheets separated by an α-helix (β-α-β)
Description for quaternary structure?
How two or more polypeptides interact to form a protein
Which type of interaction plays a key role in determining both the secondary and tertiary structure of a protein?
Hydrogen bonds.
A protein is initially driven into its tertiary structure by what type of interactions?
Hydrogen exclusion
Changes in pH affect an enzyme because the interaction of charged amino acid residues in the enzyme are affected by ______.
Hydrogen ion concentrations.
Which interactions help determine a protein's tertiary structure?
Hydrophobic exclusion, hydrogen bonds, ionic bonds, and disulfide bridges
Changes in a protein's shape can alter its ability to function or even cause it to become biologically _____.
Inactive
How does temperature affect the functioning of an enzyme?
Increasing the temperature outside the optimal range for an enzyme can alter the enzyme's structure and impair its function.
The binding of a substrate usually produces a slight change in the enzyme's shape resulting in a better enzyme-substrate fit; this is called _____ fit.
Induced
A substance that binds to an enzyme and decreases its activity is called a(n)
Inhibitor
What describes the activity of a particular enzyme?
It can be affected by substances which bind the enzyme and alter its shape.
If the interactions that maintain the 3-dimensional shape of a protein are disrupted so that the polypeptide chains completely unfold, how is this protein described?
It is denatured.
What describes the active site of an enzyme?
It's the part of the enzyme where the substrate fits.
Which of the following is unique for each kind of protein?
Its sequence of amino acids and its 3-dimensional shape
Which of the following determines the function of a protein molecule?
Its shape
Why do most enzymes function maximally in a narrow range of temperature?
Lower temperatures prevent the formation of the substrate-enzyme complex while higher temperatures can denature the enzyme.
A more efficient way to catalyze a sequence of related biochemical reactions is to combine several proteins into a ______ complex; in this way, the product of each reaction can be delivered to the next enzyme, without being released to diffuse away.
Multi-enzyme
When several enzymes that catalyze different steps of a sequence of reactions are associated with one another in a noncovalently bonded assembly, they form a(n) _____ complex.
Multi-enzyme
In general, where are nonpolar and polar amino acids found in a folded protein?
Nonpolar: interior Polar: Exterior
Most human enzymes function best between 35 and 40οC, while the enzymes of bacteria that inhabit hot, sulfur springs have a higher ______ temperature.
Optimal
What is an accurate description of a coenzyme?
Organic molecules that temporarily attach to an enzyme and promote a chemical reaction without being changed during the reaction
The _____, _____, and _____ structural levels of a protein describe a protein with a single polypeptide chain.
Primary, secondary, tertiary
The amino acid sequence of its polypeptides is called the ____ structure of a protein.
Primary.
The structure of _____ is usually discussed in terms of a hierarchy of 4 levels.
Protein
What are enzymes?
Proteins or RNA molecules that act as catalysts.
A protein that is composed of multiple polypeptides is said to have a ______ level of protein structure.
Quaternary
Which of the following level(s) of protein organization involve(s) two or more polypeptide chains?
Quaternary
What can a protein's final structure include?
Regions shaped like an α-helix and regions shaped like a β-pleated sheet.
When their normal environment is reestablished, some proteins may spontaneously refold back into their natural shape. What is this process called?
Renaturation
Description for secondary structure?
Repetitive folding patterns such as alpha helix and beta pleated sheet
Regular interaction of groups within the polypeptide backbone make up which level of the protein's structure?
Secondary
Regarding polypeptides, the two basic types of _____ structures are alpha _____ and beta-pleated sheet.
Secondary, helix
Hydrogen bonds between the amino and carboxyl groups of the polypeptide backbone help determine protein ______ structure while the hydrogen bonds between the amino acids side chains help determine protein _____ structure.
Secondary, tertiary
Which characteristic of a protein determines its function?
Shape
______ or reactants, are molecules that bind to an enzyme at the active site and are converted to products in chemical reactions.
Substrates
Individual polypeptides within a protein are referred to as which of the following?
Subunits
How can the functioning of an enzyme be affected by the external environment?
Temperature and pH can greatly affect the function of some enzymes by causing denaturation.
The tertiary structure of a protein is determined primarily by interactions involving which of the following?
The R groups of the amino acids
What is the primary structure of a protein?
The amino acid sequence of the polypeptides.
Which part of an amino acid is always acidic?
The carboxyl group
What happens if a chemical substance binds to an enzyme and alters its shape?
The enzyme's activity can be increased or decreased.
Description for primary structure?
The linear sequence of amino acids
Description for tertiary structure?
The overall 3-D shape of each polypeptide
Examples of protein domains:
The region of a protein that binds to DNA The region of a protein that activates transcription
The 20 common amino acid are classified into five chemical classes based on which of the following?
Their R groups
Which describes denatured proteins?
They are usually inactive.
What do enzymes do to the activation energy?
They lower the activation energy of a reaction by binding to the substrates.
How many different kinds of enzymes are known?
Thousands
True or false: Substances can bind to an enzyme and change its shape, affecting its activity.
True
During protein synthesis, amino acids are linked together using a ______ reaction. As a result, a peptide bond is formed.
dehydration or condensation
How do ionic bonds contribute to a protein's shape?
formation of a bond between groups with opposite charge
How do disulfide bridges contribute to a protein's shape?
formation of a covalent bond between 2 cysteine side chains
How do hydrophobic exclusion contribute to a protein's shape?
hydrophobic portions of the protein gather in the interior of the protein
Temperature affects chemical reactions in the following way: increasing the temperature of an uncatalyzed reaction _____ the rate of that reaction.
increase
The covalent bond that join two amino acids is called a ____ bond.
peptide
When a protein spontaneously refolds back into its natural shape after returning to its normal environment, this is called
renaturation
How do van der Waals attraction contribute to a protein's shape?
weak attraction between atoms due to oppositely polarized electron clouds
What are the two basic types of secondary structure in proteins?
α- helix and β-pleated sheet.
