Nucleus and Protein Synthesis Notes

Cytoplasm and Organelles

• Cytoskeletal Elements

  • Structure and function: provide structural support, shape, and motility to cells.

  • Comprised of microfilaments, intermediate filaments, and microtubules.

• Centrioles

  • Role in cilia and flagella formation: they serve as basal bodies that anchor these structures.

• Cell Extensions

  • Cilia: Short, hair-like structures that aid in movement and sensory functions.

  • Microvilli: Finger-like projections that increase surface area for absorption; structurally supported by actin filaments.

Ribosomes, Endoplasmic Reticulum, and Golgi Apparatus

• Ribosomes

  • Sites of protein synthesis, composed of ribosomal RNA (rRNA) and proteins.

• Endoplasmic Reticulum (ER)

  • Rough ER: Studded with ribosomes; involved in protein synthesis and processing.

  • Smooth ER: Lacks ribosomes; involved in lipid synthesis and detoxification.

• Golgi Apparatus

  • Modifies, sorts, and packages proteins for secretion or delivery to other organelles.

  • Functional interrelationships: Ribosomes synthesize proteins, the ER processes them, and the Golgi apparatus modifies and ships them.

Lysosomes and Peroxisomes

• Lysosomes: Contain digestive enzymes to break down waste and cellular debris.

• Peroxisomes: Involve in lipid metabolism and detoxifying harmful substances; contain enzymes like catalase.

Mitochondria

• Structure and function: double-membraned organelles, known as the powerhouses of the cell, generating ATP through cellular respiration.

Nucleus

• The largest organelle, housing the cell's genetic material.

• Responds to internal and external signals to regulate protein synthesis.

• Cell types:

  • Most cells: Uninucleate.

  • Skeletal muscle and certain bone cells: Multinucleate.

  • Red blood cells: Anucleate.

Nuclear Structure

• Nuclear Envelope: Double membrane that protects the nucleus; is continuous with rough ER and has nuclear pores for molecular transport.

• Nucleoli: Sites of ribosome assembly, larger in growing cells.

• Chromatin: DNA-protein complex that condenses into chromosomes during cell division.

Chromatin and DNA Structure

• Made of nucleosomes: clusters of histone proteins connected by DNA.

• DNA condenses into rod-like structures (chromosomes) before cell division.

• DNA Structure Metaphor:

  • DNA is a book (chromosomes) with chapters (genes), paragraphs (exons), and interruptions (introns).

Noncoding RNAs

• 98% of human genome consists of noncoding regions; doesn't encode proteins but regulates genetic functions.

• Noncoding RNAs play important roles in DNA and RNA regulation, influencing gene expression.

Gene Expression Regulation

• All body cells contain identical DNA, yet express different genes due to regulatory elements.

• Activators promote transcription, while repressors inhibit it.

Protein Synthesis Overview

• Proteins are made of amino acid chains; each gene contains instructions (DNA segment) for a polypeptide.

• Four nucleotide bases (A, G, T, C) form codons that specify amino acids.

Genetic Code

• Gene expression involves translating the DNA sequence to generate proteins.

• Eukaryotic Genome Composition: genes consist of coding exons and noncoding introns.

• Main steps: Transcription (DNA to RNA) and Translation (RNA to amino acids).

RNA Types and Functions

• mRNA: Copy of DNA sequence, codons match with DNA triplet.

• tRNA: Carries amino acids; contains anticodon that complements mRNA codon.

• rRNA: Structural component of ribosomes, facilitates tRNA and mRNA binding.

Transcription Process

• Involves transferring gene info from DNA to mRNA with the help of RNA polymerase.

• The antisense strand of DNA is used to create mRNA.

RNA Splicing

• Noncoding introns are removed, and exons are joined before mRNA exits the nucleus; allows for alternative splicing to create different proteins from the same gene.

Translation Process

• Converts mRNA sequence into an amino acid sequence at the ribosome.

• Initiator tRNA binds to the start codon on mRNA, and ribosomal subunits assemble to facilitate synthesis.

Ribosome Function during Translation

• mRNA binds to the ribosome, tRNA delivers amino acids, creating peptide bonds between them to extend the protein chain until a stop codon is reached.

Summary of Lecture Outcomes

• Outline structures and functions of the nuclear envelope, nucleolus, and chromatin.

• Define genes and genetic codes, explain gene functions, and phases of protein synthesis.

• Contrast triplets, codons, and anticodons.