Genetics And Evolution Molecular Basis Of Inheritance 8

Introns and Exons#

• Introns: These are non-coding regions within a gene that do not directly code for a part of the protein. They are transcribed into the pre-mRNA but are removed during RNA processing.
• Exons: These are coding regions within a gene that contain the information for creating a functional protein. Exons are joined together after introns are removed to form mature mRNA.

Function of Cap (5’ Cap)#

• The 5’ cap is a modified guanosine nucleotide added to the 5’ end of mRNA. Its functions include:
  • Protecting mRNA from degradation.
  • Aiding in the transport of mRNA out of the nucleus.
  • Facilitating translation initiation by interacting with translation factors.

Processing and Splicing#

• Processing: The modification of pre-mRNA to mature mRNA, including capping, polyadenylation, and splicing.
• Splicing: The removal of introns (non-coding regions) and joining of exons (coding regions) in pre-mRNA to form mature mRNA.

The First Nucleotide Being Added During Transcription#

• During transcription, the first nucleotide added to the growing RNA strand is usually adenine (A), complementary to the template DNA’s thymine (T).

The Substrates for Transcription#

• The substrates for transcription are ribonucleoside triphosphates (rNTPs), including ATP, UTP, CTP, and GTP, which serve as the building blocks for the RNA molecule.

Protein Synthesis or Translation#

• Protein synthesis, also known as translation, is the process of synthesizing proteins from mRNA. It involves three key steps: initiation, elongation, and termination.

What Are Proteins?#

• Proteins are large biomolecules made up of amino acid chains. They serve various functions in cells, including enzymatic catalysis, structural support, transportation, and signaling.

Types of Amino Acids#

• There are 20 different types of amino acids that can be incorporated into proteins. Each amino acid has a unique side chain (R-group) that determines its properties.

Organization of Protein Structure#

• Protein structure is organized into four levels:
  1. Primary Structure: The linear sequence of amino acids in the polypeptide chain.
  2. Secondary Structure: Local folding patterns like alpha helices and beta sheets.
  3. Tertiary Structure: The three-dimensional folding of the entire polypeptide chain.
  4. Quaternary Structure: The arrangement of multiple polypeptide subunits in a multi-subunit protein.

Nucleotides Necessary to Specify a Single Amino Acid#

• Three nucleotides, known as a codon, are necessary to specify a single amino acid during translation. Each codon corresponds to a specific amino acid.

Characteristics of Genetic Code#

• The genetic code is universal, redundant, and non-overlapping. It consists of 64 codons, with three serving as stop codons to terminate translation.

Process of Translation#

• Translation is the process of converting mRNA into a functional protein. It involves ribosomes, tRNA molecules, and amino acids. The main stages are initiation, elongation, and termination.

Structure of tRNA#

• Transfer RNA (tRNA) molecules are cloverleaf-shaped and carry amino acids to the ribosome during translation. They have an anticodon that pairs with the mRNA codon and a binding site for the amino acid.

Charging of tRNA#

• Charging of tRNA involves attaching the appropriate amino acid to its corresponding tRNA molecule. This process is catalyzed by aminoacyl-tRNA synthetases.

Initiation of Protein Synthesis#

• Initiation involves assembling the ribosome on the mRNA and the binding of the initiator tRNA carrying methionine (AUG) to the start codon.

Bacterial Ribosome#

• Bacterial ribosomes consist of a small (30S) and a large (50S) subunit. They are involved in protein synthesis in prokaryotic cells.

Eukaryotic Ribosomes#

• Eukaryotic ribosomes are larger and more complex, consisting of a small (40S) and a large (60S) subunit. They are involved in protein synthesis in eukaryotic cells.