Download CH 3 - Cells: The Living Units

CH 3 - Cells: The Living Units
Section 1: Overview of the Cellular
Basis of Life (p. 62)
Cellular Diversity
• Cell
- Basic structural & functional unit of living organisms.
• Diversity of Cells
- Over 200 different types of human cells
- Cells vary greatly in size, shape, & function
Generalized Cell
• All human cells have some common structures
Even though all cells have the same basic
parts,human
it’s thecell
number
•internal
Three basic
parts:& combination of
1)those
Plasma
membrane
parts
that gives each cell it’s specific
- Flexible outer boundary
function.
2) Cytoplasm
- Intracellular fluid containing organelles
3) Nucleus
- Control center
CH 3 - Cells: The Living Units
Section 2: The Plasma Membrane –
Structure (pp. 63-67)
Plasma Membrane: Structure
• Plasma Membrane
- flexible, double membrane surrounding every cell
- sometimes referred to as a “cell membrane”
- composed of lipids & proteins
- plays critical role in cellular activity
- separates intracellular fluid from extracellular fluid
Plasma Membrane: Structure
• Phospholipids
- 75% of membrane; lipid bi-layer
- Phosphate heads; hydrophilic
- Fatty acid tails; hydrophobic
• Glycolipids
- 5% of membrane
- Act as markers for cell identification
• Cholesterol
- 20% of membrane
- Maintains membrane stability & flexibility
Plasma Membrane: Structure
• Membrane Proteins
- Responsible for the specialized membrane functions
• Membrane protein functions:
- Transport of molecules in/out of cell
- Act as receptors for signals to/from the cell
- Provide ability to recognize & attach to adjacent cells
Plasma Membrane: Structure
Transport of molecules…
Plasma Membrane: Structure
Sending & receiving signals…
Plasma Membrane: Structure
Recognizing & attaching to other cells…
Plasma Membrane: Structure
• Membrane Junctions
- Bind individual cells w/ other cells
- Allows cells to communicate w/ others to function correctly
• Three main types of junctions:
1) Tight junctions
2) Desmosomes
3) Gap junctions
Plasma Membrane: Structure
• Tight Junctions
- Prevent fluids/most molecules from moving between cells
- Cells fused together by proteins
- Found in places where you don’t want fluids to leak out of
tissues (e.g., digestive tract, blood vessels, etc.)
Plasma Membrane: Structure
• Desmosomes
- Act as “rivets” or “spot-welds” that anchor cells together
- Prevent cells from separating
- Reduce chances of tearing when subjected to pulling forces
- Found in areas under mechanical stress (Skin, Heart, etc.)
Plasma Membrane: Structure
• Gap Junctions
- “Communication” junction between cells
- Hollow cylinders; allow molecules to pass from cell to cell
- Found in areas that need to move ions & other substances
between cells (Cardiac cells, Smooth muscle)
CH 3 - Cells: The Living Units
Section 3: The Plasma Membrane –
Transport (pp. 68-79)
Plasma Membrane: Transport
• Interstitial Fluid
- water-based fluid surrounding all cells in our body
- “Soup” of amino acids, sugars, fatty acids, vitamins,
hormones, neurotransmitters, & salts
• Membrane Transport
- Plasma membranes are selectively permeable
- Some molecules easily pass through; others do not
- Substances pass to/from inside of cell & interstitial fluid
Animation: Membrane Permeability
Plasma Membrane: Transport
• Types of Membrane Transport
1) Passive processes
- No cellular energy (ATP) is required
2) Active processes
- Cellular energy (ATP) is always required
- Require specialized carrier proteins
Plasma Membrane: Passive Transport
• Types of passive processes:
1) Diffusion (aka “Simple Diffusion”)
- Movement of molecules from high to low concentration
- DOWN the concentration gradient
- Molecules inherently WANT to move apart
- Speed is influenced by temperature & particle size
(Higher temps = faster diffusion; Smaller particles = faster diffusion)
Examples = Oxygen, Carbon dioxide, Fat-soluble vitamins
Animation: Diffusion
Plasma Membrane: Passive Transport
• Types of passive processes:
2) Facilitated Diffusion
- Molecules move down concentration gradient
- Must have either carrier proteins or channel proteins
- Particles are either too large to pass through the bi-layer
or they are charged particles that are repelled
- Rate of diffusion is limited by number of carriers/channels
Plasma Membrane: Passive Transport
• Types of passive processes:
2) Facilitated Diffusion
- Channels may be open all the time (“Leakage” channels)
- Channels may be controlled by chemical/electrical signals
(“Gated” channels)
Leakage channel
Gated channel
Plasma Membrane: Passive Transport
• Types of passive processes:
3) Osmosis
- Diffusion of water thru selectively permeable membranes
- Water moves very freely through lipid bi-layers
- Water concentration determined by solute concentration
**In this case, b/c solutes cannot diffuse, water will instead. It
moves from high water concentration (low solute concentration) to
low water concentration (high solute concentration).
Plasma Membrane: Passive Transport
• Importance of Osmosis
- When osmosis occurs, water enters or leaves cell
- Changes in cell volume disrupt cell function
• Tonicity
- Ability of a solution to cause a cell to shrink or swell
Animation: Osmosis
Plasma Membrane: Tonicity
• Isotonic solution
- Solution with same solute
concentration as the cytoplasm
- Cells in these solutions maintain
the same volume
- Our extracellular fluid is isotonic
Plasma Membrane: Tonicity
• Hypertonic solution
- Solution with greater solute
concentration than cytoplasm
- Cells in these solutions lose
water & shrink (“crenate”)
- Dehydration leads to this
Plasma Membrane: Tonicity
• Hypotonic solution
- Solution with lower solute
concentration than cytoplasm
- Cells in these solutions gain
water & can burst (“lyse”)
Plasma Membrane: Active Transport
• Types of active processes:
1) Active transport
- Requires carrier proteins & ATP
- Moves molecules against concentration gradient
- Solutes “pumped” from low to high concentration
Example = Na+-K+ pump (found in all cells)
Plasma Membrane: Active Transport
• Types of active processes:
2) Vesicular transport
- Requires ATP
- Cell uses vesicles (hollow capsules) to move large
substances in/out
- Also called “bulk” transport
Plasma Membrane: Active Transport
Endocytosis:
- bulk transport of substances INTO the cell
2 Types:
1) Phagocytosis
- Using pseudopods to engulf solids
- “Eating”
- Macrophages, white blood cells
Plasma Membrane: Active Transport
Endocytosis:
- bulk transport of substances INTO the cell
2 Types:
2) Pinocytosis
- Membrane infolds, bringing in
extracellular fluid
- “Drinking”
- Nutrient absorption in small intest.
Plasma Membrane: Active Transport
Exocytosis:
- bulk transport of substances OUT of the cell
Examples:
1) Hormone secretion
2) Neurotransmitter release
3) Mucus secretion
CH 3 - Cells: The Living Units
Section 4: The Cytoplasm,
Organelles, & Nucleus (pp.81-95)
The Cytoplasm
• Cytoplasm
- located between the plasma membrane & nucleus
- site where most cellular activities are accomplished
Composed of:
1) Cytosol
- water w/ solutes (proteins, salts, sugars, etc.) in it
2) Organelles
- metabolic machinery of the cell
3) Inclusions
- glycogen, pigments, lipid droplets, crystals, vacuoles
Cytoplasmic Organelles
• Cytoplasmic Organelles
- “little organs”
- specialized components that perform specific jobs in cell
- work together to help cell carry out its specific function
1) Mitochondria
- Power plants of cell; provide cell with ATP
- Contain their own DNA & RNA
- Found in abundance in cells requiring huge quantities of
energy (kidney, liver, muscle, etc.)
Cytoplasmic Organelles
2) Ribosomes
- Sites of protein synthesis
- Cells are protein factories; all proteins made by the cell
are built here
- May be floating freely in cytoplasm or attached to
endoplasmic reticulum Ribosomes
Cytoplasmic Organelles
3) Endoplasmic Reticulum (ER)
- Interconnected network of passageways through cell
Two Types:
a) Rough ER
- surface is studded w/ ribosomes
- make all proteins that are to be secreted by cell
- build proteins that will be incorporated into lipid bi-layer
- particularly abundant in secretory cells & liver cells
Cytoplasmic Organelles
3) Endoplasmic Reticulum (ER)
- Interconnected network of passageways through cell
Two Types:
b) Smooth ER
- surface is smooth
- involved in lipid/cholesterol/glycogen breakdown
- deals w/ detoxification of drugs & carcinogens
- builds steroid-based hormones
- abundant in liver, kidney, & intestinal cells
Cytoplasmic Organelles
4) Golgi Apparatus
Animation: Endomembrane System
- modifies, concentrates, & packages proteins
- proteins pass from ER into Golgi apparatus
- proteins placed in vesicles & transported throughout cell
Cytoplasmic Organelles
5) Lysosomes
- membranous bags containing digestive enzymes
- break down ingested bacteria, viruses, & toxins
- degrade nonfunctional organelles
- break down bone to release calcium
- destroy cells in injured tissue
Cytoplasmic Organelles
6) Peroxisomes
- membranous sacs containing oxidases/catalases
- function to detoxify alcohol
- most importantly, they neutralize free radicals (chemicals
that scramble biological molecules)
Cytoplasmic Organelles
7) Cytoskeleton
- elaborate series of “rods” running throughout the cytosol
- provides a framework that supports all cellular structures
2 Main Types:
a) Microfilaments
- involved in cell motility, change in cell shape, &
endocytosis/exocytosis
Cytoplasmic Organelles
7) Cytoskeleton
- elaborate series of “rods” running throughout the cytosol
- provides a framework that supports all cellular structures
2 Main Types:
b) Microtubules
- hollow tubes that can change in shape, size, & location
- determine overall cell shape & placement of organelles
Cytoplasmic Organelles
10) Cilia
- small, hair-like extensions on the surface of cells
- move in a wavelike motion propelling substances across
the surfaces of cells (cells lining the respiratory system)
11) Flagella
- long, tail-like extensions that rotate & propel the entire
cell through a solution (sperm)
Cytoplasmic Organelles
12) Microvilli
- fingerlike extensions of plasma membrane
- increase surface area for absorption
- very extensive in the lining of the small intestine
Cytoplasmic Organelles
13)Nucleus
- genetic library w/ blueprints for all cellular proteins
- responds to various signals & determines type & amount
of proteins to be made
- most cells have 1 nucleus
- red blood cells have no nucleus
- skeletal muscle cells have multiple nuclei
Cytoplasmic Organelles
14) Nuclear Envelope
- double membrane surrounding nucleus; porous
- pores regulate transport of molecules into/out of nucleus
15) Nucleoli
- spherical bodies in nucleus
- produce new ribosomes that are sent out thru pores in
nuclear envelope into the cytoplasm
CH 3 - Cells: The Living Units
Section 5: Cell Growth &
Reproduction (pp.95-107)
Cell Growth
• Cell Cycle
- series of changes cells go through from formation to
reproduction
- includes interphase & cell division/mitosis
Cell Growth
• Interphase
- period from cell formation to beginning of cell division
- cell is essentially doing all routine activities & growing
Subphases:
1) G1 phase (Gap 1) – cell is metabolically active, building
proteins, & growing vigorously
2) S phase (synthetic) – DNA replication
3) G2 phase (Gap 2) – enzymes & other proteins needed for
division are made
G0 phase – only seen in cells that never divide; continue to
function normally until death
Cell Growth
• Cell Division
- period of time where the cell splits into 2 smaller cells
- essential for body growth & tissue repair
- very short amount of time compared to interphase
Two distinct events:
1) Mitosis
- nuclear division
- prophase, metaphase, anaphase, telophase
2) Cytokinesis
- division of the cytoplasm
Mitosis
Stages of Mitosis (Quick overview)
1) Prophase
- chromosomes become visible
- nuclear envelope breaks down
- spindle fibers begin to form
Mitosis
Stages of Mitosis
2) Metaphase
- chromosomes line up at the cell’s equator
- spindle fibers attach to the chromosomes
Mitosis
Stages of Mitosis
3) Anaphase
- spindle fibers pull chromosomes to opposite poles of cell
- poles of cell itself begin to be pushed apart
- cell starts to elongate
Mitosis
Stages of Mitosis
4) Telophase
- begins when chromosome movement stops
- nuclear membrane forms around each set of DNA
- spindle fibers disappear
- cytokinesis can now be completed
Control of Cell Division
WHY cells divide…
- Cells function most efficiently at a very specific size
- when they become too large, surface area of the plasma
membrane isn’t large enough to match the cell’s volume
- large cells have difficulty taking in nutrients & getting rid
of wastes fast enough to maintain life
- when cells grow above the optimum size, they divide
Control of Cell Division
HOW cells divide…
- various factors involved in control of cell division
•
“Go” signals
- chemicals that respond to large cell size
- growth factors, growth hormones, cyclins
•
“Stop” signals
- p53 gene creates proteins that inhibit cell division (more
than half of all cancers have defective p53 genes)
- contact inhibition; cell grows until it touches another cell
Protein Synthesis
Remember…
- cells are protein factories
- DNA holds the information for building proteins
Gene
- segment of DNA that codes for an individual protein
- can be broken down into triplet groups (3 bases each)
- each triplet (“codon”) specifies an individual amino acid
Protein Synthesis
Central Dogma of Genetics
Transcription
DNA → RNA → protein
Translation
*The ultimate goal of the cell is to turn DNA into protein.
In order to do that, the cell must use an intermediate step
involving RNA.
Protein Synthesis
Three main types of RNA:
1) Messenger RNA (mRNA)
- carries the re-written instructions for building proteins
from the nucleus to the ribosome
- disposable copy of the blueprint
2) Ribosomal RNA (rRNA)
- structural component of the ribosome
- helps to physically combine amino acids into a protein
Protein Synthesis
Three main types of RNA:
3) Transfer RNA (tRNA)
- carries amino acids from the cytoplasm to the ribosome
- ribosome takes amino acid; releases tRNA back into
cytoplasm to pick up new amino acid
Protein Synthesis
Steps of protein synthesis:
1) Transcription
- process of converting (“rewriting”) DNA blueprint into
mRNA so that it can be “read” by ribosomes.
2) Translation
- process of converting (“translating”) mRNA into an amino
acid sequence (a.k.a. “protein”)
Protein Synthesis - Transcription
Protein Synthesis - Translation
Protein Synthesis
Genetic Code:
- each mRNA codon specifies individual amino acids
- there are 64 letter combinations for codons & 20 different
amino acids
- some amino acids have more than one codon
Protein Synthesis
So here’s how it works…
- All proteins start with the mRNA codon “AUG”
- All proteins end with 1 of 3 mRNA codons (“UAA”, “UAG”,
“UGA”)
Protein Synthesis
Role of Rough ER…
Developmental Aspects of Cells
• Body cells contain the same DNA; but aren’t all identical
• Cell differentiation
- Chemical signals in the embryonic stage of development
channel cells down certain pathways by turning off
certain genes
- Gives each cell a specific function/role within the body
Theories of Cell Aging
Why do we get old???
- various theories exist explaining why our cells age & die
1) Wear & Tear Theory
- over time, chemical “attacks” & free radicals have a
cumulative effect, wearing the cell out
2) Immune System Disorders
- Autoimmune responses & progressive weakening of
immune response damages cells
Theories of Cell Aging
Why do we get old???
- various theories exist explaining why our cells age & die
3) The Genetic Theory
- Termination of mitosis & cell aging are programmed into
genes
- Number of times a cell can divide may be pre-determined
Young Katie Holmes
Not-so-young Katie Holmes