4.1 Biological molecules (3)
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1.
State that large molecules are made from smaller molecules. Explain, naming the smaller molecules involved, how the following large biological molecules are formed:
- Starch
- Proteins
- Cellulose
Large biological molecules, also known as macromolecules, are polymers formed from repeating smaller monomer units. Here's how the specified molecules are formed:
- Starch: Starch is a polysaccharide formed from glucose monomers. Glucose molecules are linked together by glycosidic bonds to create long chains and branched structures. This process is called polymerisation.
- Proteins: Proteins are polymers made from amino acid monomers. Amino acids are joined together by peptide bonds. This process also involves polymerisation, where amino acids are linked in a specific sequence to form polypeptide chains. These chains then fold into complex 3D structures.
- Cellulose: Cellulose is a polysaccharide formed from glucose monomers. Similar to starch, glucose molecules are linked by glycosidic bonds. However, the glycosidic bonds in cellulose are different from those in starch, making cellulose chains more linear and rigid. This results in the strong, structural properties of cellulose.
2.
List the chemical elements that make up carbohydrates.
Carbohydrates are composed of the elements carbon (C), hydrogen (H), and oxygen (O). The general formula for carbohydrates is (CH2O)n, indicating a consistent ratio of these elements.
3.
Explain how the structure of DNA, specifically the double helix and the base pairing rules, contributes to the process of DNA replication.
The structure of DNA is fundamental to DNA replication. The double helix structure provides a template for the synthesis of new DNA strands. During replication, the two strands of the DNA molecule unwind and separate. Each separated strand serves as a template for the synthesis of a new complementary strand.
The base pairing rules (A-T and C-G) are crucial. DNA polymerase, the enzyme responsible for DNA replication, uses these rules to ensure that the new strands are made with the correct sequence of bases. For example, if the template strand has an adenine (A), the DNA polymerase will add a thymine (T) to the new strand.
This complementary base pairing allows each new DNA molecule to consist of one original strand and one newly synthesized strand. This is known as semi-conservative replication. The double helix structure also ensures that the new strands are properly aligned and that the replication process is accurate, minimizing errors in the genetic code. The helical structure also allows for efficient access of enzymes to the DNA template.