20 if two proteins contain the same type and number of amino acids, but the order in which they link up is different, are the properties of the two proteins the same?
21 what are enzymes, and for what purpose are they usually used?
22 what is the \lock and key\ theory of enzyme action?
23 what are the basic parts of a nucleotide?
24 how does dna store information?
25 what holds the two helices in a dna molecule together?
26 what is the term for the unraveling of enzymes when they are heated or exposed to a ph out of their optimal range? how does it affect the ability of a protein to function?

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Accepted Answer

### Question 20
# Brief Explanations:
Proteins' properties depend on their 3D structure, which is determined by amino acid sequence (primary structure). Different sequences (even same amino acids, different order) lead to different folding (secondary, tertiary, quaternary structures), so properties (like function, solubility, reactivity) differ.
# Answer:
No, the properties of the two proteins are not the same. Because a protein’s properties are determined by its three - dimensional structure, and the three - dimensional structure is ultimately determined by the sequence of amino acids. Even with the same type and number of amino acids, a different linkage order (amino acid sequence) will result in a different three - dimensional structure, thus leading to different properties.

### Question 21
# Brief Explanations:
Enzymes are biological catalysts (usually proteins, some RNA) that speed up chemical reactions in cells. They lower activation energy, enabling reactions (like digestion, metabolism) to occur at physiological conditions, increasing reaction rates without being consumed.
# Answer:
Enzymes are biological catalysts, usually proteins (and in some cases RNA molecules). Their main purpose is to speed up chemical reactions in living organisms by lowering the activation energy required for the reaction to occur. This allows biochemical reactions (such as those involved in metabolism, digestion, and DNA replication) to proceed at a rate that is suitable for the functioning of the cell or organism.

### Question 22
# Brief Explanations:
The “lock and key” theory states that an enzyme (lock) has a specific active - site shape complementary to its substrate (key). The substrate fits into the enzyme’s active site like a key into a lock, forming an enzyme - substrate complex. This specific binding allows the enzyme to catalyze the reaction of the substrate.
# Answer:
The “lock and key” theory of enzyme action proposes that enzymes have a specific three - dimensional structure at their active site. This active site has a shape that is complementary to the shape of a specific substrate (or substrates). Just as a key fits into a lock, the substrate fits into the enzyme's active site, forming an enzyme - substrate complex. Once the substrate is bound in this way, the enzyme can facilitate the chemical reaction that transforms the substrate into the product (or products). After the reaction, the product (or products) is released from the enzyme, and the enzyme is then available to bind with another substrate molecule.

### Question 23
# Brief Explanations:
A nucleotide, the building block of nucleic acids (DNA, RNA), has three basic parts: a 5 - carbon sugar (deoxyribose in DNA, ribose in RNA), a phosphate group ($PO_4^{3 - }$), and a nitrogen - containing base (adenine, thymine/uracil, guanine, cytosine).
# Answer:
A nucleotide has three basic parts:
1. A five - carbon sugar: In DNA, this sugar is deoxyribose, and in RNA, it is ribose.
2. A phosphate group ($PO_4^{3-}$) which is responsible for the negative charge of the nucleotide and forms the backbone of the nucleic acid chain.
3. A nitrogen - containing base: The nitrogen - containing bases can be adenine (A), guanine (G), cytosine (C), thymine (T, in DNA only), or uracil (U, in RNA only).

### Question 24
# Brief Explanations:
DNA stores information in the sequence of its nitrogen - containing bases (adenine, thymine, guanine, cytosine). The order of these bases (like a genetic “code”) in the DNA molecule forms genes, which encode instructions for making proteins (and other functional molecules). Groups of three bases (codons) can code for specific amino acids, and the overall sequence of codons in a gene determines the amino acid sequence of a protein.
# Answer:
DNA stores information in the sequence of its nitrogen - containing bases (adenine, thymine, guanine, and cytosine). The specific order of these four bases along the DNA molecule forms a kind of “code”. This code is organized into units called genes. Each gene contains the instructions for making a particular protein (or, in some cases, a functional RNA molecule). The sequence of bases in a gene determines the sequence of amino acids in a protein, as groups of three bases (known as codons) correspond to specific amino acids. By having different sequences of these four bases, DNA can encode the vast amount of information needed to direct the development, growth, and functioning of an organism.

### Question 25
# Brief Explanations:
In a DNA molecule, the two strands of the double helix are held together by hydrogen bonds between the complementary nitrogen - containing bases. Adenine (A) forms two hydrogen bonds with thymine (T), and guanine (G) forms three hydrogen bonds with cytosine (C).
# Answer:
The two helices (strands) in a DNA molecule are held together by hydrogen bonds between the complementary nitrogen - containing bases of the two strands. Specifically, adenine (A) on one strand forms two hydrogen bonds with thymine (T) on the other strand, and guanine (G) on one strand forms three hydrogen bonds with cytosine (C) on the other strand.

### Question 26
# Brief Explanations:
The term for the unraveling of enzymes (and other proteins) due to heat or non - optimal pH is denaturation. Denaturation disrupts the protein's specific three - dimensional structure (including the active site). Since the enzyme's activity depends on the specific shape of the active site, denaturation causes the enzyme to lose its catalytic activity as the substrate can no longer bind effectively to the altered active site.
# Answer:
1. The term for the unraveling of enzymes when they are heated or exposed to a pH out of their optimal range is denaturation.
2. Denaturation affects the ability of a protein (enzyme) to function because it causes the protein to lose its specific three - dimensional structure, including the precise shape of the active site. The active site is the region of the enzyme where the substrate binds and the reaction is catalyzed. When the active site loses its specific shape due to denaturation, the substrate can no longer bind to the enzyme effectively, and thus the enzyme loses its catalytic activity (the ability to speed up the chemical reaction).

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