BMS 107 - Cell Outline Summer-1 PDF

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The Cell I.

The Study of Cells: cytology a. only visible by microscopy

II.

Types of Microscopy a. Light Microscopy (LM): visible light passes through the cell b. Transmission Electron Microscopy (TEM): a beam of electrons passes through the cell can magnify about 100X greater than LM c.

III.

Scanning Electron Microscopy (SEM): beam of electrons bounces off surface of the cell to provide a 3D study of the cell surface

Cellular Functions a. Covering b. Lining c.

Storage

d. Movement e. Connection f.

Defense

g. Communication h. Reproduction IV.

A Prototypical Cell: a generalized cell (not a real cell in the body – combines features from many different cells) a. Most human cells have three basic parts: i. Plasma (cell) membrane! ii. Cytoplasm iii. Nucleus

Prototypical+Cell+

V.

Plasma (Cell) Membrane a. An extremely thin outer border on cell b. Serves as a selective physical and chemical barrier deciding what comes into and leaves the cell c.

VI.

the “gatekeeper” that regulates the passage of gases, nutrients, and wastes between the internal and external environments of the cell

Plasma+Membrane+

General Functions of the Plasma (Cell) Membrane a. Communication b. Intercellular connection c.

Physical barrier!

d. Selective permeability

VII.

Composition and Structure of Membranes: two molecular components: a. Lipids: i. Two layers: outer and inner 1. Insoluble in water . . . prevents cells from dissolving in water 2. 3 types of lipids in membranes: a) Phospholipids i. The majority of lipids in cell membranes ii. Each has a polar (charged) region and nonpolar (uncharged) region iii. When exposed to aqueous (water) environment, they form a phospholipid bilayer 1. polar regions face outside and inside of the cell 2. nonpolar regions face each other (form internal core of the membrane)

Phospholipid+bilayer+

b) Cholesterol i. about 20% of all membrane lipids ii. strengthens and stabilizes membrane against extreme temperature c) Glycolipids i. about 5–10% of all membrane lipids ii. have carbohydrate (sugar) molecules attached facing out and forming the glycocaylx b. Membrane Proteins i. Lipids are majority of structure but proteins give membrane functions ii. Proteins: complex molecules made of amino acids chains iii. 2 types of membrane proteins:

1. Integral: a) Embedded in phospholipid bilayer b) Span the entire thickness of the membrane c) Exposed to the outside and inside of the cell d) Also termed transmembrane proteins e) Can have carbohydrates (sugars) attached to outer surface = glycoproteins f)

The glycoproteins and the glycolipids form the glycocalyx on the external surface of the plasma membrane

g) Have many varied functions

2. Peripheral: a) Not embedded in the lipid bilayer b) Loosely attached to the external or internal surface of the plasma membrane c) Protein-Specific Functions of the Plasma (Cell) Membrane: i. Transport ii. Intercellular connection iii. Anchorage for the cytoskeleton iv. Enzyme activity v. Cell–cell recognition vi. Signal transduction

VIII.

Crossing the Membrane: 2 general types of membrane transport:

a. Passive: i. All involve diffusion – no energy required from the cell, substances move from areas of high concentration to low ii. 4 types of diffusion: 1. Simple diffusion – example: movement of O2 from lungs (higher concentration to blood (lower concentration) 2. Osmosis - diffusion of water 3. Facilitated diffusion – requires a protein transporter (integral protein) 4. Bulk filtration – movement of large amounts of substances (fluids/solvents and solutes)

b. Active: i. requires energy from the cell ii. materials are moved up or against concentration gradient iii. Bulk Transport (not filtration): 1. Moves large molecules or bulk structures across the plasma membrane 2. Requires energy from the cell 3. Can go in either direction: a) Exocytosis: out of the cell i. materials to be secreted out of cell and are packaged into vesicles (secretory) ii. vesicles fuse with plasma membrane and materials are released b) Endocytosis: into the cell i. materials are taken into the cell packaged into vesicles

IX.

Types of Endocytosis a. Phagocytosis: nonspecific uptake of particles by formation of membrane extensions (pseodopodia) that surround particles to be engulfed b. Pinocytosis: nonspecific uptake of extracellular fluid c.

Receptor-mediated endocytosis: engulfing of specific molecules bound to receptors on the surface of the plasma membrane

X.

Cytoplasm: all materials (solid and liquid) between plasma membrane and nucleus a. Cytosol : i. A viscous, syruplike fluid containing many different dissolved substances such as: 1. Ions, Nutrients, Proteins, Carbohydrates, Amino acids b. Inclusions: i. Large storage aggregates of complex molecules found in the cytosol ii. Examples: 1. Melanin: pigment in skin cells 2. Glycogen: long chains of sugars in the liver and skeletal muscles c.

Organelles (see image of prototypical cell above): i. Means “little organs” ii. Many types, each perform different function(s) iii. The type and number of organelles within a cell is a reflection of the cell’s function

XI.

Organelles can be classified in two types: i. Membrane-bound ii. Non-membrane-bound

XII.

Membrane-Bound Organelles a. Biochemical activity in organelle is isolated (separate) from cytosol and other organelles b. Examples are: i. Endoplasmic reticulum (ER): a network of intracellular membrane-bound tunnels (enclosed spaces are called cisternae) 2 types of ER:

1. Smooth endoplasmic reticulum (SER) a) Walls have a smooth appearance b) Continuous with RER c) Functions include: i. Synthesis, transport, and storage of lipids including steroid hormones ii. Metabolism of carbohydrates iii. Detoxification of drugs, alcohol, and poisons

2. Rough endoplasmic reticulum (RER) a) walls appear rough due to attachment of ribosomes on outside of the RER membrane (ribosomes synthesize proteins) b) The RER functions to synthesize, transport, or store proteins for: i. Secretion by the cell ii. Incorporation into the plasma membrane iii. Creation of lysosomes

ii. Golgi apparatus (complex) 1. Stacked cisternae whose lateral edges bulge, pinch off, and give rise to small transport and secretory vesicles 2. Function to receive proteins and lipids from the RER for modification, sorting, and packaging a) Receiving region is the cis-face b) Shipping region is the trans-face c) Protein Flow through the Golgi Apparatus: i. Proteins synthesized in RER get packaged into transport vesicles. ii. Transport vesicles pinch off from RER and fuse with the receiving cis-face of the Golgi apparatus. iii. The proteins move between and are modified in the cisternae of the Golgi apparatus. iv. Modified proteins are packaged in secretory vesicles.

v. Secretory vesicles either participate in exocytosis or become lysosomes in the cell

iii. Lysosomes 1. Vesicles generated by the Golgi apparatus 2. Contain enzymes used to digest and remove waste products and damaged organelles within the cell (autophagy) 3. When a cell is dying it releases lysosomal enzymes that digest the cell (autolysis)

iv. Peroxisomes 1. Vesicles smaller than lysosomes 2. Use O2 and an enzyme (catalase) to detoxify harmful molecules taken into the cell

v. Mitochondria 1. Bean-shaped organelles with double membrane 2. inner membrane folded into shelf-like cristae 3. internal fluid: matrix 4. Function to produce a high energy containing molecule called ATP on the cristae 5. Cells that require more energy have more mitochondria than cells requiring less energy

Mitochondria+

XIII.

Non-Membrane-Bound Organelles: in direct contact with the cytosol a. Ribosomes: i. Comprised of a large and small subunit ii. Responsible for protein synthesis iii. Free ribosomes float unattached within the cytosol iv. Fixed ribosomes are attached to the outer surface of RER b. Cytoskeleton: i. Proteins organized in the cytosol as solid filaments or hollow tubes ii. 3 main protein types: 1. Microfilaments: Maintain and change cell shape; participate in muscle contraction and cell division 2. Intermediate filaments: Provide structural support and stabilize junctions between apposed cells 3. Microtubules a) Fix organelles in place b) Maintain cell shape and rigidity c) Direct movement of organelles in the cell d) Allow cell motility (in cilia and flagella)

Cytoskeleton+

c.

Centrosomes and centrioles i. Centrosome: a pair of centrioles at right angles to each other ii. Centriole: nine sets of microtubule triplets 1. involved in organizing microtubules 2. attached to chromosomes during cell division causing chromosomal migration

d. Cilia: grouped on cells that move objects across their surface i. Example: cells of the respiratory tree and oviduct) e. Flagella: longer, usually singular, to propel a cell (e.g., sperm)

f.

Microvilli: Extensions of cell, not capable of motion; much smaller than cilia i. Increase the surface area to increase absorption of food; found on surface of cells of the small intestine

XIV.

Nucleus a. Control center for cellular activity b. Contains DNA (deoxyribonucleic acid), a complex molecule containing: i. chromatin when not dividing (nuclear DNA is unwound into fine filaments) ii. chromosomes during cell division (tight coils of chromatin)

XV.

Aging and the Cell a. Aging is a normal and continuous process b. indicated by changes in number of organelles or chromatin structure c.

Cells can die in two general ways: i. Pathological damage or necrosis ii. Programmed cell death or apoptosis

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