Cells Chapter 3

Introduction Cells vary greatly in size, shape, content, and function depending on their purpose

Composite Cell Impossible to describe a “typical” cell Composite cell Includes almost all cell structures, but does not actually exist Used to show different parts of cell

Composite Cell

3 Basic Parts of Cell 1. Cell Membrane “City wall” Encloses the cell Semi-permeable

Cell Membrane Also called “plasma membrane” Actively functioning and selectively permeable— the membrane chooses what goes in and out Structure: Lipids, proteins, and carbohydrates Phospholipid bilayer Phosphate head = hydrophilic “water loving” Fatty Acid tail = hydrophobic “fears water”

* Phospholipids make up the membrane with proteins embedded to help regulate what comes across the membrane

3 Basic Parts of Cell 2. Nucleus – “mayor of city” Houses genetic material Controls cell activities has “nuclear pores” in membrane Contains nucleolus: small, dense body of RNA and protein that creates ribosomes

3 Basic Parts of Cell 3. Cytoplasm Fills out the cell Holds the organelles Organelles: specialized structures within the cell; “tiny organs”

OrganelleFunction Cell Membrane Nucleus Nucleolus Mitochondrion Vesicle Rough ER Smooth ER Lysosome Golgi Apparatus Golgi Vesicles Ribosome Cytoplasm Microtubules Centrioles

Organelles Mitochondria - “energy plant” - site of cellular respiration - creates ATP (used for energy)

Organelles Vesicles - “taxi” - membranous sacs - bring substances into and out of cell Lysosome - “garbage disposal” - digestive sacs that use enzymes to break down bulky molecules

Organelles Golgi Apparatus - “post office” - refines, packages, and delivers proteins from the ER - Golgi Vesicles: responsible for transporting the proteins

Organelles Endoplasmic Reticulum – “Highways and road systems” – Transport system; passageways connect membrane to nucleus and to organelles in cell - Smooth ER: lipid synthesis (for membrane) - Rough ER: contains ribosomes for protein synthesis (sent from nucleolus)

Organelles Ribosomes - “lumber/brick yard” - use ingredients from RNA and amino acids to assemble proteins

Organelles Microtubules - “steel girders” - composed of protein “tubulin” - form cytoskeleton of cell (provide structure) Centrioles - “plastic surgeons” - help to split the chromosomes and divide the cell

3.3 – Movement through Cell Membranes Two types: Passive (does not require energy) Active (requires energy)

Passive Mechanisms 1. Diffusion Passes through lipid bilayer Molecules spread from HIGH to LOW across the concentration gradient Seeks equilibrium: balanced, uniform state Concentration gradient – difference in concentration of molecules

Diffusion

Passive Mechanisms 2. Facilitated Diffusion Facilitated = uses help Used if particles are too big to pass through membrane Use proteins as passageways

Facilitated Diffusion

Passive Mechanisms 3. Osmosis Diffusion of water molecules through protein channels Isotonic – balance of osmotic pressure Hypertonic – too much water leaving cell (high osmotic pressure outside cell) Hypotonic – too much water entering cell (low osmotic pressure outside cell)

Osmotic Pressure

Passive Mechanisms 4. Filtration Forces molecules through membranes (typically blood vessels)

Active Mechanisms 1) Active Transport – moves particles from LOW to HIGH concentrations against the concentration gradient using carrier molecules carriers can be called “pumps” Uses ATP for energy

Active Mechanisms 2. Endocytosis- brings large particles INTO the cell a) Pinocytosis – “cell drinking”; takes in liquids and dissolved particles b) Phagocytosis – “cell eating”; takes in solids such as debris and bacteria c) Receptor-mediated endocytosis- moves SPECIFIC particles into the cell Attach to “LIGANDS” Attachment is called a “receptor-ligand combination”

Active Mechanisms 3. Exocytosis – moves large particles OUT of cell using vesicle fusion (debris or small particles) 4. Transcytosis – Combines endocytosis and exocytosis to move particles all the way through the cell Used for very specific purposes Ex: To test food for foreign particles

Section 3.4 The Cell Cycle Series of changes in a cell from when it forms to when it divides

Mitosis ● Growth and repair ● 1 division ● Full set of chromosomes (46 chromosomes)

Meiosis Purpose: preparation for reproduction 2 divisions Half set of chromosomes (23 chromosomes) Result: eggs (female) and sperm (male)

Interphase LONGEST phase in cell cycle 3 stages G1 phase: duplication of organelles outside nucleus S phase (synthesis): genetic material replicates G2 phase: the rest of organelles duplicate

Prophase Centrioles move to opposite ends of cell Nuclear envelope disappears Chromatin condenses into chromosomes Spindle fibers form

Metaphase Chromosomes line up at equator Spindle fibers attach to centromeres

Anaphase Spindle fibers shorten Chromosomes separate and move to ends of cell

Telophase Chromosomes are at either end of cell Chromosomes “unwind” into fibers Nuclear envelope reforms Cytokinesis begins

Cytokinesis Division of membrane and cytoplasm Membrane constricts (cleavage furrow) Cell separates into two new cells

After Division the Cell may… 1. Die – this is called APOPTOSIS 2. Continue dividing and producing more cells – STEM CELLS 3. Become specialized; for example, turn into a nerve cell or bone cell – DIFFERENTIATION