Chapter 3 Cells 3 1 Introduction Cells vary

Chapter 3 Cells

3. 1 -- Introduction �Cells vary greatly in size, shape, content, and function depending on their purpose �Over 200 different types of human cells

3. 2 -- 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 �Everything found outside the cell is known as extracellular material.

Composite Cell

3 Basic Parts of all Human Cells 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”

Organelle Function 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) http: //www. youtube. com/watch? v=d. PKv. Hr. D 1 e. S 4

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 �Use proteins as passageways �Used if particles are too big to pass through membrane

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

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 foreign particles

Section 3. 4 The Cell Cycle �Series of changes in a cell from when it forms to when it divides

Mitosis ● Purpose: Growth and repair ● 1 division ● Results in 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 � 4 stages �G 1 phase: cell grows and duplication of organelles outside nucleus occurs �S phase (synthesis): genetic material replicates �G 2 phase: cell finishes growing and duplicating organelles; acts as a checkpoint �G 0 phase: brief resting phase (or possibly permanent– ex: neurons)

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