Cell Division PDF

Cell Division Overview: Events of cell division Mitosis Functions of Cells: Metabolize, digest food, - division of the nucleus dispose of wastes, reproduce, grow, move, and - Results in the formation o...

Cell Division Overview: Events of cell division Mitosis Functions of Cells: Metabolize, digest food, - division of the nucleus dispose of wastes, reproduce, grow, move, and - Results in the formation of two daughter respond to stimuli. nuclei Cell Life Cycle: Cytokinesis - is a series of changes the cell - division of the cytoplasm experiences from the time it is formed - Begins when mitosis is near completion until it divides - Results in the formation of two daughter cells Involves two periods: Mitosis (Nuclear Division): 1. Interphase (metabolic phase): - The cell grows and carries out normal 1. Prophase: functions - Chromatin condenses into - Longer phase of the cell cycle. chromosomes,identical strands called chromatids are held together by a button-like body called centromere. - Centrioles direct the assembly of mitotic spindle forms, - nuclear envelope and nucleoli breaks down. 2. Cell Division: - The cell reproduces itself, preparing for division through DNA replication. DNA Replication: Genetic material is duplicated and readies a cell for division into two cells Occurs towards the end of interphase. Process of DNA replication - DNA uncoils, creating two nucleotide chains, each serving as a template. - Nucleotides pair complementary bases: A-T, G-C. Metaphase: - A cleavage furrow (contractile ring of - Chromosomes align in the center of the microfilaments) forms to pinch the cells cell on the metaphase plate ( center of into two parts the spindle midway between the - Two daughter cells exist centrioles) - Straight line of chromosomes is now seen - In most cases, mitosis and cytokinesis Anaphase: occur together - Chromatids separate and move to - In some cases, the cytoplasm is not opposite ends of the cell. divided - Anaphase is over when the - Binucleate or multinucleate cells result chromosomes stop moving - Common in the liver and skeletal muscle Cytoplasmic Pressure - tension between chromosomes in the cells - Gives rise to prophase Protein Synthesis Telophase: DNA - Chromosomes uncoil to become - provides the template for building chromatin, nuclear envelope reforms proteins. around chromatin, spindle breaks down. - Nucleoli appear in each of the daughter Gene nuclei - DNA segment that carries a blueprint for building one protein or polypeptide Cytokinesis (Cytoplasmic Division): chain - Division of the cytoplasm - Begins during late anaphase and completes during telophase Proteins have many functions Messenger RNA (mRNA) Fibrous (structural) proteins - Carries the instructions for building a - are the building materials for cells protein from the nucleus to the ribosome Globular ( functional) proteins Protein synthesis involves two major phases: - acts as enzymes (biological catalysts) Transcription & Translation DNA information is coded into a sequence of bases Transcription (DNA to RNA) A sequence of the three bases (triplet) codes for - Transfer of information from DNA's an amino acid base sequence to the complementary base sequence of mRNA Role of DNA - DNA is the template for transcription; - Most ribosomes, the manufacturing sites mRNA is the product of proteins, are located in the cytoplasm - Each DNA triplet corresponds to an - DNA never leaves the nucleus in mRNA codon interphase cells - If DNA sequence is AAT-CGT-TCG, - DNA requires a decoder and a then the mRNA corresponding codons messenger to carry instructions to build are UUA-GCA-AGC proteins to ribosomes - Stops until 60 - Both the decoder and messenger functions are carried out by RNA Translation (RNA to Protein) (ribonucleic acid) - Base sequence of nucleic acid is translated to an amino acid sequence; Difference of RNA to DNA amino acids are the building blocks of - RNA is a single stranded helix proteins - RNA contains ribose sugar instead of - Occurs in the cytoplasm and involves deoxyribose and contains uracil (U) base three major varieties of RNA instead of thymine (T) STEP 1: Covers transcription Three varieties of RNA Step 2: mRNA leaves nucleus and attaches to Transfer RNA (tRNA) ribosome, and translation begins - Transfers appropriate amino acids to the Step 3: incoming tRNA recognizes a ribosome for building the protein complementary mRNA codon calling for its amino acid by temporarily binding its anticodon Ribosomal RNA (rRNA) to the codon - Helps form the ribosomes where Step 4: as the ribosome moves along the mRNA, proteins are built a new amino acid is added to the growing protein chain Step 5: released tRNA reenters the cytoplasmic pool, ready to be recharged with a new amino acid  The plasma is selectively permeable barrier - Some materials can pass through, while other are excluded ex. Nutrients can enter the cell Undesirable substances are kept out Methods of transport Passive processes/transport - substances are transported across the membrane without any input or energy from the cell Active transport - the cell provided the metabolic energy (ATP) to drive the transport process Membrane Transport Passive transport Solution Diffusion - homogenous mixture of two or more - Molecule movement is from high components concentration to low concentration, down a concentration gradient Solvent - Particles tend to distribute themselves - dissolving medium present in the larger evenly within a solution quantity; the body’s main solvent is - Kinetic energy (energy of motion) water causes the molecules to move about randomly Solutes - Size of the molecule and temperature - components in smaller quantities within affect the speed of diffusion a solution Molecules will move by diffusion if any of the Intracellular fluid following applies: - Nucleoplasm and cytosol The molecules are small enough to pass - Solution containing gasses, nutrients and through the membrane's pores (channels formed salts dissolved in water by membrane proteins) The molecules are lipid-soluble Extracellular fluid (interstitial fluid) The molecules are assisted by a membrane - Fluid on the exterior of the cell carrier - Contains thousands of ingredients, such as nutrients, hormones, neurotransmitters, salts, waste products Types of Diffusion - Filtration is critical for the kidneys to work properly Simple Diffusion - an unassisted process Active Processes - Solutes are lipid- soluble or small - ATP is used to move substances across a enough to pass through membrane pores membrane - Active processes are used when: Osmosis - simple diffusion of water across a A. Substances are too large to travel selectively permeable membrane through membrane channels - Highly polar water molecules easily B. The membrane may lack special protein cross the plasma membrane through carriers for the transport of certain aquaporins substances - Water moves down its concentration C. Substances may not be lipid-soluble gradient D. Substances may have to move against a concentration gradient Osmosis (A Closer Look) - Isotonic solutions have the same solute - Active transport and vesicular transport and water concentrations as cells and - Active transport cause no visible changes in the cell - Amino acids, some sugars, and ions are - Hypertonic solutions contain more transported by protein carriers known as solutes than the cells do; the cells will solute pumps begin to shrink - ATP energizes solute pumps - Hypotonic solutions contain fewer solutes (more water) than the cells do; In most cases, substances are moved against cells will plump concentration or electrical gradients Facilitated diffusion ex. - Transports lipid-insoluble and large sodium-potassium pump substances Necessary for nerve impulses - Glucose is transported via facilitated Sodium is transported out of the cell Potassium diffusion is transported into the cell - Protein membrane channels or protein molecules that act as carriers are used Passive Processes (continue) Filtration - Water and solutes are forced through a membrane by fluid, or hydrostatic, pressure - A pressure gradient must exist that pushes solute-containing fluid (filtrate) from a high-pressure area to a lower-pressure area Vesicular transport - substances are moved across the membrane “in bulk” without actually crossing the membrane Types of Vesicular Transport Exocytosis - Mechanism cells use to actively secrete hormones, mucus, and other products - Material is carried in a membranous sac called a vesicle that migrates to and combines with the plasma membrane - Contents of vesicle are emptied to the outside Endocytosis - Extracellular substances are enclosed (engulfed) in a membranous vesicle - Vesicle detaches from the plasma membrane and moves into the cell - Once in the cell, the vesicle typically fuses with a lysosome - Contents are digested by lysosomal enzymes - In some cases, the vesicle is released by exocytosis on the opposite side of the Exocytosis docking process cell - Docking proteins on the vesicles recognize plasma membrane proteins and bind with them Types of endocytosis - Membrane corkscrew and fuse together 1. Phagocytosis-"cell eating" - Cell engulfs large particles such as bacteria or dead body cells - Pseudopods are cytoplasmic extensions that separate substances (such as bacteria or dead body cells) from external environment - Phagocytosis is a protective mechanism, not a means of getting nutrients 2. Pinocytosis-"cell drinking" - Cell "gulps" droplets of extracellular fluid containing dissolved proteins or fats - Plasma membrane forms a pit, and edges fuse around droplet of fluid - Routine activity for most cells, such as those involved in absorption (small intestine) 3. Receptor-mediated - Method for taking up specific target molecules - Receptor proteins on the membrane surface bind only certain substances - Highly selective process of taking in substances such as enzymes, some hormones, cholesterol, and iron