Protein Synthesis and RNA Quiz

Protein Synthesis

• Protein synthesis is the process where cells create proteins, the fundamental building blocks with diverse functions
• Divided into two main stages: transcription and translation
• DNA carries the genetic blueprint, consisting of two strands forming a double helix, each strand with nucleotides containing a sugar (deoxyribose), phosphate, and one of four nitrogenous bases (adenine, thymine, cytosine, guanine)

RNA

• RNA (ribonucleic acid) is a single-stranded molecule that helps convert the genetic code from DNA to proteins
• RNA differs from DNA in that it contains ribose as its sugar and uracil instead of thymine

Transcription

• Transcription is the process of copying a DNA segment into mRNA, occurring within the nucleus
• RNA polymerase binds to the promoter region, initiating the process
• The DNA strands unwind, and RNA polymerase creates a new mRNA strand using complementary RNA nucleotides matching the DNA template strand
• RNA polymerase moves along the DNA, adding RNA nucleotides (5' to 3' direction) to form a growing mRNA strand
• Transcription ends when RNA polymerase reaches a termination sequence; mRNA is then released and prepared for further processing

Translation

• Translation is deciphering mRNA sequence into a polypeptide chain (folds into a functional protein) within the cytoplasm at ribosomes
• Initiation: Small ribosomal subunit links to mRNA near the start codon (AUG); initiator tRNA with methionine attaches. The large subunit joins, completing the ribosome
• Elongation: tRNA carrying specific amino acids enter the ribosome's A site; the anticodon pairs with corresponding mRNA codon. A peptide bond forms between amino acids. Ribosomes shift, moving empty tRNA to the E site and the growing chain to the P site, preparing for the next tRNA
• Termination: The ribosome reaches a stop codon. Release factors detach the polypeptide chain; the ribosomal subunits separate

DNA Replication

• DNA replication is a crucial step in the cell cycle, ensuring each daughter cell receives an exact copy of DNA
• Initiation: DNA helicase unwinds the DNA double helix at specific sites (origins of replication), creating replication forks
• Elongation: DNA polymerase adds complementary nucleotides to each template strand in a 5' to 3' direction; The leading strand is continuous, the lagging strand is discontinuous (Okazaki fragments), joined by DNA ligase
• Termination: Replication continues until the entire DNA molecule is copied, producing two identical DNA molecules (one original and one new strand)

Mitosis

• Mitosis, somatic cell division, creates two genetically identical daughter cells
• Divided into four phases:
  • Prophase: Chromatin condenses to form visible chromosomes; nuclear envelope disintegrates; mitotic spindle forms
  • Metaphase: Chromosomes align at the metaphase plate; spindle fibers attach to centromeres
  • Anaphase: Sister chromatids separate and move to opposite poles of the cell
  • Telophase: Chromosomes reach poles, decondense. Nuclear envelopes reform, producing two nuclei in the original cell
  • Cytokinesis: Cytoplasm divides, creating two separate daughter cells, each with a complete set of chromosomes

Control of Cell Division

• Cell division is strictly regulated by checkpoints (G1, G2, and M) to ensure proper conditions and prevent errors
• G1 Checkpoint: Determines if the cell is ready for DNA replication
• G2 Checkpoint: Verifies DNA duplication completeness
• M Checkpoint: Ensures accurate chromosome alignment before separation

Necrosis and Apoptosis

• Necrosis: Uncontrolled cell death due to injury, toxins, or infection, causing inflammation and tissue damage
• Apoptosis: Programmed cell death, a controlled process crucial in development, tissue homeostasis, and eliminating damaged or harmful cells

Meiosis

• Meiosis is a reproductive cell division creating genetically diverse gametes (half the chromosome number)
• Meiosis I: Homologous chromosomes separate, reducing the chromosome number to haploid (n)
• Meiosis II: Sister chromatids separate, creating four haploid cells

Multiple Choice Questions

• Multiple choice questions provided for review of concepts, covering enzymes in DNA replication, chromosomal alignment in mitosis, RNA types, stages of translation, ensuring cells with damaged DNA don't proceed to mitosis, and the significance of meiosis