Cell: Structure and Function Transcription and Translation Nestor T. Hilvano, M.D., M.P.H.

Learning Objectives You should be able to: 1. Discuss the basic concepts of the cell theory. 2. Describe the structure and functions of cell membrane. 3. List the main organelles of a cell and explain their functions. 4. Discuss the structure and functions of the cell nucleus and explain the importance of genetic code. 5. Describe the process of protein synthesis. 6. Explain the relationship between cell division and cancer.

Cell Theory Concepts 1. All organisms are composed of cells. 2. Cells are the smallest units that perform vital functions. 3. Cells come only from preexisting cells. 4. Each cell maintains homeostasis at the cellular level. 2 general classes of Human body cell 1. sex cells are ___. 2. somatic cells are ___. a. body cells b. reproductive cells

Parts of Cell ___ = outer boundary of cell. ___ = contents of cell, the cytosol and intracellular structures ___ = contain DNA essential for controlling cellular activities. A. Nucleus B. Cell (plasma) membrane C. Cytoplasm

Cell (Plasma) Membrane Functions – physical isolation, regulates exchange, sensitivity, and structural support Components: a. phospholipid bilayer b. integral (channel) proteins c. cholesterol ___ What component forms physical barrier? ___ What are responsible for transport of molecules into and out of the cell (facilitated transport)?

Organelles Membranous - endoplasmic reticulum - golgi apparatus - lysosomes - mitochondria - peroxisomes Nonmembranous - cytoskeleton - centrioles - ribosomes

Organelles ___ - parallel, flattened membranous sacs covered with ribosomes; synthesis of packaged protein for export. ___ – lack ribosomes; synthesis of lipids, cholesterol, glycogen, calcium, and carbohydrates, detoxify drugs ___ - granules of protein and RNA, free and attached; synthesis of protein for cell use a. Smooth endoplasmic reticulum b. Ribosomes c. Rough endoplasmic reticulum

Organelles ___ - flattened sacs (cisternae); modify and package secretions ___ – usually oval; intracellular removal of damaged organelles ___ - doubled membrane; production of ATP (energy) ___ - oval bodies; secretes oxidative enzymes ___ - short cylindrical assembly of microtubules; important for movement of chromosomes in cell division a. mitochondria b. golgi apparatus c. peroxisomes d. lysosomes e. centrioles

Cytoskeleton Main functions: structural/supporting framework of cell Types: ___ – globular protein tubulin, provide shape, cell strength, anchoring of organelles ___ – smallest cytoskeleton composed of protein actin, produce cell movement ___ – composition varies among cells, provide strength, stabilize position of organelles, transport materials within the cytoplasm a. Microfilaments b. Intermediate filaments c. Microtubules

Nucleus Contains the genetic materials Nuclear envelope - doubled membrane with perinuclear space and nuclear pores * Function of nuclear pores: passage of ions/materials Nucleoplasm –Chromatin = DNA and protein –Nucleoli = dark masses, contain RNA

Organization of DNA within the nucleus DNA strands coiled around histones to form nucleosomes Nondividing cells – chromatin (fine, filamentous) Dividing cells – chromosomes (chromatins condenses/coils) What is a gene? _________________

Protein synthesis: Transcription Transcription –mRNA is formed next to an activated gene (DNA) –copying instructions from DNA to mRNA (RNA polymerase binds to DNA) Pre-mRNA is unfinished –“nonsense” (introns), “sense” (exons) Given a DNA template of TACCGC, what is the corresponding codon in mRNA transcribed? _______________

Protein Synthesis: Translation Takes place in cytoplasm Ribosome attaches to m-RNA t-RNA (anticodons) - interprets the message Amino acids assembled into protein molecule Exercise: What anticodons of t-RNA (translation) are formed to codons AUGGCG of m-RNA? _______________________

Cell Cycle Interphase (resting stage) G 1 phase –accumulates materials to replicate DNA; cell growth S phase (synthesis phase) –DNA replication (sister chromatids) G 2 phase –replicates centrioles –synthesizes enzymes for division Mitotic (M phase) –Nuclear division (mitosis) and cytoplasmic division (cytokinesis) –one cell divides into 2 daughter cells with identical copies of DNA –Functions: embryonic development, tissue growth, replacement of dead cells, repair of injured tissues

Consequences of uncontrolled cell division Tumors (neoplasms) –abnormal growth, cells multiply faster than they die a) Benign – non-cancerous; localized tumor, does not spread to distant organs b) Malignant – cancerous, metastatic tumor, spread to distant organs

Homework (Self- review) 1. Define key terms: cytoplasm, nucleus, organelles, gene, transcription, translation, nuclear pores, introns, exons, codons, channel protein, exocytosis, endocytosis. 2. State the function/s of the following: golgi apparatus, centrioles, mitochondria, rough ER, smooth ER, ribosomes, cytoskeletons, lysosome, peroxisomes 3. Describe the components of plasma membrane and its functions. 4. Differentiate benign from malignant tumor.