Genes, Proteins, and Inheritance

 

What Are Genes and Proteins?

• Genes:

  • A gene is a section of DNA that provides the instructions to make a specific protein.
  • These proteins determine the traits (e.g., eye color, height) of an organism.
  • Think of genes as "blueprints" for building your body.

• Proteins:

  • Proteins are made up of amino acids and perform important functions, such as:
    • Acting as enzymes to speed up reactions.
    • Providing structure (e.g., collagen in skin).
    • Helping with communication (e.g., hormone proteins).

 

Inheritance of Sex

XY & XX Chromosomes

• A Chromosome pair determine the sex of an organism.
• This is different to most other characteristics which are determined by either one or a number of genes
• Females have the XX sex chromosomes
• Males have the XY sex chromosomes
• The sex of a child is determined by the father. This is because only the father is the carrier of the Y chromosome.
• The sperm produced by a man, half will have the X chromosome and half will carry the Y chromosome.
• If the X chromosome carrying sperm is fertilised a female will be formed and if a Y chromosome if fertilised then a male will be formed

• How Sex Is Determined:

  • X sperm + mother's X = female (XX)
  • Y sperm + mother's X = male (XY)

   

 

Inheritance of Genes

• Chromosomes Carry Genes:
  • Genes are found on chromosomes, which are thread-like structures in the nucleus.
  • Each human cell has 46 chromosomes (23 pairs).

Key Concept	Explanation
Diploid Nucleus	Contains two sets of chromosomes (23 pairs).
Haploid Nucleus	Contains one set of chromosomes (e.g., in sperm and egg cells).

• Inheritance:
  • Alleles: Different forms of the same gene.
    • Example: The gene for eye color can have blue or brown alleles.
  • An individual inherits one allele from each parent.

 

How Do Genes Make Proteins?

1. DNA Contains Instructions:

   • DNA is made of a sequence of bases (A, T, C, G).
   • The order of these bases determines the sequence of amino acids in a protein.

2. mRNA Is the Messenger:

   • A copy of the gene is made as mRNA (messenger RNA).
   • mRNA carries the instructions from the nucleus to the ribosomes.

3. Ribosomes Build Proteins:

   • Ribosomes read the mRNA and assemble amino acids into a protein.
   • The sequence of amino acids determines the protein's shape and function.

 

Steps in Protein Synthesis	Details
Gene remains in the nucleus.	DNA stays in the nucleus to protect the genetic information.
mRNA copies the gene.	A copy of the gene's instructions is made in the form of mRNA.
mRNA moves to the cytoplasm.	The mRNA leaves the nucleus and goes to the ribosomes.
Ribosomes assemble proteins.	Amino acids are joined together in the correct order to form a protein.

 

Why Are Proteins Important?

• Proteins control cell functions by:

  • Acting as enzymes to control chemical reactions.
  • Being receptors for communication (e.g., neurotransmitter binding).
  • Helping with transport (e.g., hemoglobin carries oxygen in the blood).

• Proteins are unique because the sequence of amino acids determines their shape, and shape determines their function.

 

How Does DNA Control Traits?

• All body cells contain the same DNA, but:

  • Not all genes are active in every cell.
  • Example: A liver cell will only "turn on" genes needed for liver function.

• Different active genes = Different proteins = Different cell functions.