DNA and Protein Production (translation and transcription) 10/09

Definition: A gene is a segment of DNA that contains the instructions for making a specific protein (or polypeptide).
Expression of a Gene: A gene is expressed when the protein it codes for is produced in the cell.
Functional Units of Heredity: Genes are the functional units of heredity and determine which proteins a cell makes and ultimately its traits.

Selective Gene Expression: Only certain genes are active (expressed) in each cell type, with most genes turned off in any given cell.
Specialization: Active genes produce specific proteins that determine the structure and function of that cell.
- Example:
  - Muscle cells express genes for contractile proteins.
  - Nerve cells express genes for neurotransmitters.

Control Mechanisms: Cells manage which genes are activated based on their requirements to ensure proteins are synthesized only when required.
- Regulation Factors:
  - Transcription Factors: Proteins that turn genes on or off.
  - Cell Signals and Hormones: Can activate or suppress gene expression.
  - Environmental Factors: Such as temperature, light, or chemicals.
Significance of Regulation: Proper regulation maintains cell efficiency and function, allowing adaptation and specialization while conserving energy.

Insulin Production
- The insulin gene is present in every cell but is only expressed in pancreatic β (beta) cells.
- When blood glucose levels rise, these cells activate the insulin gene, producing insulin protein.
- Insulin is secreted into the bloodstream to lower blood sugar levels.
Melanin Production
- Melanin: The pigment which provides color to skin, hair, and eyes.
- The gene for melanin is active only in melanocytes (specialized skin cells).
- Expression of the gene leads to production of enzymes (like tyrosinase) that create melanin.
- Sunlight can increase gene expression, resulting in more melanin and a darker skin tone (tanning).
- Environmental Influence: Shows how external factors can influence gene expression in specialized cells.

Promoter: A DNA sequence upstream of the gene that initiates transcription and acts as a binding site for RNA polymerase.
Exon: The coding region of a gene that contains instructions for building proteins.
Intron: The non-coding region of a gene that is removed from the mRNA before translation.

Definition: Transcription is the process of making an RNA copy of a DNA gene and takes place in the nucleus.
Differences Between RNA and DNA:
- RNA is single-stranded.
- RNA contains uracil (U) instead of thymine (T).
- RNA has ribose as its sugar, whereas DNA has deoxyribose.
Significance: Transcription is the first step in gene expression, converting DNA information into RNA form.

Nucleotides:
- RNA Nucleotide: Contains ribose sugar with an OH group and the bases adenine (A), uracil (U), cytosine (C), and guanine (G).
- DNA Nucleotide: Contains deoxyribose sugar and the bases adenine (A), thymine (T), cytosine (C), and guanine (G).
Strands:
- DNA is double-stranded (forms a double helix).
- RNA is single-stranded (flexible and shorter).
Functionality:
- DNA functions primarily in the nucleus while RNA functions primarily in the cytoplasm.

Steps:
- The introns are removed, and exons are joined. Exons are the expressed sequences that contain coding information.
- RNA polymerase links RNA nucleotides to synthesize mRNA.
- The mRNA strand is formed and exits the nucleus to participate in translation in the cytoplasm.

Definition: Translation is the process of reading mRNA to produce a polypeptide chain (protein) and occurs at the ribosome in the cytoplasm.
Genetic Code - Codons:
- mRNA consists of codons, which are three-nucleotide sequences that code for specific amino acids.
- Each codon represents one amino acid, thus forming the building blocks of proteins.

tRNA (transfer RNA) carries a specific amino acid to the ribosome.
- Anticodon on tRNA pairs complementary to the codon on mRNA ensuring the correct amino acid is added to the growing protein chain.
Role of Ribosomal RNA (rRNA):
- rRNA forms the structure of ribosomes and facilitates peptide bond formation between amino acids during synthesis.

Initiation:
- Small ribosomal subunit binds to mRNA at the start codon (AUG).
- tRNA with the anticodon (UAC) pairs with AUG, delivering the first amino acid, methionine.
- The large ribosomal subunit joins to form a complete ribosome with A, P, and E sites.
Elongation:
- The ribosome continues reading the mRNA codons, with tRNAs bringing the correct amino acids.
- rRNA catalyzes the formation of peptide bonds, linking new amino acids to the growing polypeptide chain.
Termination:
- Process continues until a stop codon is reached (UAA, UAG, UGA).
- A release factor binds to the stop codon, releasing the completed polypeptide and detaching the ribosomal subunits for future use.

Cytosolic Proteins: Produced by free-floating ribosomes; function includes enzyme activity and structural support.
Membrane & Export Proteins: Produced by ribosomes attached to the Rough ER, destined for secretion, membrane insertion, or lysosomal use.

Structure of DNA and nucleotides, including the four bases and their pairing.
Functions and binding areas of RNA polymerase.
Transcription and translation processes, including the significance of RNA processing and examples.

Key Terms Include:
- DNA polymerase, RNA polymerase, helicase, semiconservative replication, complementary strand, point mutation, mutagens, base pairs, gene, promoter region, polypeptide chain, peptide bond, translocation, transcription, translation, codon, anticodon, intron, exon.