Biology · Chemistry

Biomolecules and Enzymes

1,501 Questions

This topic focuses on biomolecules, specifically proteins, enzymes, and amino acids. It includes questions on enzyme structures, protein folding, and catalysis. These concepts are crucial for medical and biology competitive exams.

Enzyme catalysisProtein structuresAmino acid synthesisPolypeptide chainsBiomolecule properties

Biomolecules and Enzymes Questions

Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

Three of the following statements about enzymes are correct and one is wrong. Which one of the following is wrong?

  1. Enzymes require optimum pH for maximal activity.
  2. Enzymes are denatured at high temperature but in certain exceptional organisms they are effective even at temperatures 80-90$^o$C.

  3. Enzymes are highly specific.

  4. Most enzymes are proteins but some are lipids.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Enzymes are the biological catalyst which catalyzes biological reactions within a narrow range of temperature and pH. Certain thermophiles have enzymes which remain functional even at very high temperatures. Most of the enzymes are proteins in nature but a few enzymes are RNA in nature. They are called as catalytic RNAs or ribozymes.

Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

Part of enzyme which combines with non-protein part of form functional enzyme is

  1. Apoenzyme

  2. Coenzyme

  3. Prosthetic group

  4. None of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The conjugate protein consists of two parts protein and non-protein part. Non-protein part is the cofactor and protein part is apoenzymes. Complete conjugate protein is known as Holoenzymes. Apoenzyme is an inactive enzyme. Thus, the correct option is D.

Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

Which one value is required for better enzymatic action?

  1. High K$ _i$
  2. Low K$ _i$
  3. Low K$ _m$
  4. High K$ _m$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A constant indicating the substrate concentration at which an enzyme catalysed reaction attains half its maximum velocity or 1/2 V$ _{max}$ is known as Michaelis-Menten constant or K$ _m$. Lower K$ _m$ indicates more affinity between the enzyme and substrate and consequently higher reaction rates.

Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

Combination of apoenzyme and coenzyme produces

  1. Prosthetic group

  2. Holoenzymes

  3. Enzyme-substrate complex

  4. Enzyme-product complex
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Enzymes are proteins which help to catalyze the biochemical reaction. The enzyme has a protein part which is not active is known as apoenzyme. It gets activated by the addition of an organic or inorganic cofactor. The holoenzyme is defined as apoenzyme in combination with the cofactor. 
So, the correct answer is option B.
Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

Enzymes are basically made of

  1. Nucleic acids

  2. Proteins

  3. Fats

  4. Vitamins
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Enzymes are proteins which help to catalyze the biochemical reaction. The enzyme has a protein part which is not active is known as apoenzyme. It gets activated by the addition of an organic or inorganic cofactor. The holoenzyme is defined as apoenzyme in combination with the cofactor. 
So, the correct answer is option B.
Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

Which is not a trait of enzymes?

  1. Proteinaceous nature

  2. Specific in nature

  3. Speed up rate of biochemical reaction

  4. Used up in reaction
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Enzymes are proteins which help to catalyze the biochemical reaction. The enzyme has a protein part which is not active is known as apoenzyme. It gets activated by the addition of an organic or inorganic cofactor. It is specific in nature as specific substrate bind at the active site of a particular enzyme. It increases the rate of chemical reactions without being used up. The enzymes lower the activation energy and lead to the formation of activated complex, which is also known as transition state and finally changes to the product.

So, the correct answer is option D.

Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

Which is wrong about enzymes?

  1. Enzymes are mostly proteins but some are lipids also

  2. Enzymes are highly specific

  3. Enzymes require optimum pH and temperature for maximum activity

  4. Enzymes are denatured at high temperature
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Enzymes are made up of proteins which accelerates the rate of the reaction. It lowers the activation energy and converts the reactants into the substrate. The increased temperature increases the kinetic energy of the enzymes which further accelerates the activity of the enzyme but at the higher temperature, it gets denatured as the peptide bonds between the proteins molecules breaks which disrupts the structure of enzymes. 
Enzymatic activity depends on specific pH. pH at which the enzyme has maximum activity is known as optimum pH. The change in pH changes the shape of the enzyme which prevents the attachment of the substrate at the active site and terminates the reaction. 
Enzymes are specific in nature. It forms an enzyme-substrate complex by attaching to the active site of the enzyme which depends specifically on the shape of the active site and the substrate molecules.
So, the correct answer is option A.
Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

Which is true about enzymes?

  1. All enzymes are not proteins

  2. All enzymes are vitamins

  3. All enzymes are proteins

  4. All proteins are enzymes
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Enzymes are protein in nature. But some enzymes like ribozymes and ribonuclease are RNA based enzymes. It is also known as ribonucleic acid enzymes. These are RNA molecules which helps in the catalysis of a particular reaction. It was discovered in year 1982. The RNA can act as both genetic material and can act as a biocatalyst but different from protein-based enzymes. It acts as a part of ribosome which attaches to the amino acid during protein synthesis. Thomas R. Cech and Sidney Altman discovered catalytic properties of RNA. So, the correct answer is option A.

Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

Enzyme generally have?

  1. Same pH and temperature optima

  2. Same pH but different temperature optima

  3. Different pH but same temperature optima

  4. All wrong
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The optimum temp of enzymes is 20-35°C. They become inactivated at very low temperature and denatured (destroyed) at very high temp i.e. greater than 45°C. Low molecular weight enzymes are comparatively more heat stable. In archaebacterium Pyrococcus furiosus, the optimum temperature of hydrogenase is greater than 95°C. This heat-stable enzyme enables Pyrococcus to grow at 100°C. The optimum pH of most endoenzyme is pH 7.0 (neutral pH). However, digestive enzymes can function at different pH. For example, salivary amylase act best at pH 6.8, pepsin act best at pH2 etc. Any fluctuation in pH from the optimum causes ionization of R-groups of amino acids which decrease the enzyme activity.

So the correct option is 'different pH but same temperature optima' 

Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

Serine proteases are called so because they

  1. They require serine for their activity

  2. cleave after serine residues in the substate

  3. Are inhibited by the presence of free serine

  4. Have a serine residue at their active sire
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Serine proteases are enzymes that cleave peptide bonds in proteins, in which serine serves as a nucleophilic amino acid at enzyme's active site. Serine proteases are responsible for coordinating various physiological functions including digestion, immune response, blood coagulation, and reproduction. Hence, serine proteases are called so because they require serine for their activity.

So, the correct answer is 'They require serine for their activity'.

Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

Specific enzymes are needed for the break-down of a particular substance.

  1. True

  2. False

  3. Either

  4. Neither
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Enzymes are very specific for the substances they act upon and cause their breakdown. For example, cellulase enzyme breakdowns cellulose, protease enzyme breakdowns proteins, pectinase enzyme breakdowns pectin, hemicellulose enzyme breakdowns hemicellulose and many more such enzymes are there. Enzymes are biological catalysts which increase the rate of reaction by lowering the energy of activation. High specificity is a characteristic feature of enzymes.
Hence, the statement given in the question is correct.
So, the correct answer is 'True'
Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology
Which of the following is an example of isozyme?
  1. $\alpha$-amylase

  2. Glucokinase

  3. Lactate dehydrogenase

  4. All of the above

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The multiple molecular forms of an enzyme occurring in the same organism and having a similar substrate activity are called isoenzymes or isozymes. They have similar properties but different molecular weights and locations. Over 100 enzymes are known to have isoenzymes. $\alpha$-amylase of wheat endosperm, has 16 isozymes, lactate dehydrogenase has 5 isozymes. Glucokinase is an isozyme of hexokinase.
So, the correct answer is 'All of the above'.
Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

The active site of an enzyme is formed by

  1. Exposed sulphur bonds

  2. Side chains of the amino acids

  3. Amino groups of the amino acids

  4. Carboxyl group of the amino acids
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The enzyme active site is composed of the amino acid residues. Side chains of the amino acids are seen in the active site region of the enzyme. The difference in the identity, charge, and spatial orientation of the functional groups located there results in the difference in enzyme specificity. 

So, the correct option is ' side chains of amino acids'.

Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

The enzymes are functional at 

  1. 0-5$^{\circ}$C
  2. 15-25$^{\circ}$C
  3. 25-40$^{\circ}$C
  4. 70-85$^{\circ}$C
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Enzymes works precisely at certain narrowly optimum conditions, such as appropriate temperature, pH, and ion concentration. Deviation from the optimal conditions adversely affects enzyme activity.  Most enzymes have an optimal temperature, at which the rate of reaction is fastest. For human enzymes, the temperature optima are near the human body temperature (35-40$^o$C). Enzymatic reactions occur slowly or not at all at low temperatures. As the temperature increases, molecular motion increases, resulting in more molecular collisions. The rates of most enzyme-controlled reactions, therefore, increase as the temperature increases, within limits. High temperatures rapidly denature most enzymes. The molecular conformation (3-D shape) of the protein becomes altered as the hydrogen bonds responsible for its secondary, tertiary, and quaternary structures are broken. Because this inactivation is usually not reversible, activity is not regained when the enzyme is cooled.

Multiple choice properties of enzyme enzyme properties enzymes biomolecules: chemical constituents of living cells biology

Identify the incorrect statement about enzymes.

  1. They consist of proteins, with or without a non-protein part.

  2. They change the rate of the catalyzed reaction.
  3. They change the value of $\triangle$G of the reaction.

  4. They are not sensitive to heat.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Enzymes are biological catalyst which catalyze biological reactions. Most of the enzymes are proteins in nature. Some of the enzymes have non protein part which helps them to carry out reaction. Enzymes change the rate of chemical reaction by bringing about a decrease in free energy requirement. Thus, changing the free energy of the reaction. Because enzymes are proteins, they are highly sensitive to heat. Thus, enzymes catalyze reactions only at physiological conditions of temperature and pH.