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Chapter 6 & 7 (Chapter 6 - A Tour of the Cell (Endomembrane System,…
Chapter 6 & 7
Chapter 6 - A Tour of the Cell
Fundamental Units of Life
All organisms are made of cells
Cell is the simplest collection of live matter
Cells can be different but they all share common features
Cells are related by their descent from earlier cells
Microscopy
Light Microscope
visible light passes through specimen and then through glass lenses
Effective magnification of 1,000x the size of a specimen
Too low to study organelles
Lenses
Bend light so that the image is magnified
Contrast
visible differences between parts in sample
Magnification
ratio of image size to real size
Resolution
clarity of an image
Electron Microscopes
Scanning
beam of electrons provide images that look 3-D
Transmission
Beam of electrons through a specimen, flat image
used to study internal structure of cells
Cell Fractionation
Takes cells apart and separates major organelles from one another
Centrifuges fractionate cells into their component parts
enables scientists to determine organelle functions
helps correlate function with structure
Comparing Prokaryotes and Eukaryotes
Basic features of all cells
cytosol
Chromosomes
carry genes
Plasma membrane
selective barrier that allows passage of nutrients, oxygen, and waste to pass trough
Ribosomes
make proteins
Prokaryotic Cells
Nucleoid
No membrane bound organelles
No nucleus
cytoplasm bound by plasma membrane
Eukaryotic Cells
Membrane bound organelles
Cytoplasm between plasma membrane and nucleus
DNA bound by double membrane
Nucleus
nucleus contains most of DNA in a eukaryotic cell
Ribosomes use the information from the DNA to make proteins
Nuclear envelope
encloses the nucleus,separating from cytoplasm
double membrane, lipid bilayer
Nuclear Lamina
lining of the nuclear envelope
composed of proteins
maintain nucleus shape
DNA in nucleus is organized into discrete units
Chromosomes
Each chromosome contains one DNA molecule associated with proteins
Chromatin
Nucleolus
located within nucleus
site of rRNA synthesis
Ribosomes
Made of rRNA and protein
Carry out protein synthesis in two locations
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Generally much larger than prokaryotic cells
Endomembrane System
Lysosomes
membranous sac that can digests macromolecules
work best in acidic enviornments
made by ER and then trnasferred to the Golgi App. for processing
Ability to phagocatize
a lysosome fuses with a food vacuole and digests the molecules in it
autophagy
recycling of the cells organelles and macromolecules
Vacuoles
Large vesicles derived from the Er and Golgi App.
Varying functions
Food vacuoles
formed by phagocytosis
Contractile vacuoles
pump excess water out of cells
Central vacuoles
hold organic compounds and water
Golgi apparatus
cristae
flat membranous sacs
modifies products of ER
manufactures certain macromolecules
sorting and packaging materials into transport vesicles
Plasma Membrane
Endoplasmic Reticulum
Continuous with nuclear envelope
Smooth ER
No ribosomes
Synthesizes lipids
detoxifies drugs and poisons
stores calcium ions
metabolizes carbs
Rough ER
Studded with ribosomes
ribosomes secrete glycoproteins
distributes Transport vesicles
a membrane factory for the cell
These components are either continuous or connected through transfer by Vesicles
Nuclear envelope
Energy in a cell
Mitochondria
site of cellular respiration
uses oxygen to generate ATP
cristae
folded inner membrane
inner membrane creates two spaces
intermembrane space
mitochondrial matrix
Chloroplasts
sites of photosynthesis
found in plants and algae
Shared Traits
With bacteria
free ribosomes
Shared traits with bacteria led to a theory about these cells
Endosymbiont Theory
An early ancestor of eukaryotes engulfed a cell, the cells formed a bond and the engulfed cell evolved over time to be the mitochondria or in other cases the chloroplasts
circular DNA
Double membrane
grow and reproduce somewhat independently in cells
contain green pigment called chlorophyll
Structure
thylakoid membrane
sites of photosynthesis
stroma
internal fluid
Peroxisomes
oxidative organelles
produce hydrogen peroxide and convert it to water
relation to other cells is still unknown
specialized metabolic compartments bound by a single membrane
Cytoskeleton
network of fibers extending throughout the cytoplasm
three types of structures
microfilaments
Thinnest
Actin
form cortex inside the plasma membrane
intermediate filaments
medium thickness in relation to other filaments
several different proteins
fix organelles in place
support cell shape
microtubules
Thickest
constructed of dimers of tubulin
separating chromosomes during cell division
shape the cell
guiding movement of organelles
Control beating of cilia and flagella
flagella
Common structure
group of microtubules
basal body as an anchor
motor protein called dynein
cilia
maintains cell structure
helps with motility
Cell Wall
only in plant cell
primary cell wall
secondary cell wall
middle lamella
Surface area/Volume Ratio
As a cell increases size, volume grows more than its surface area
Surface area/ Volume
Surface area increases while volume remains constant
Allows more space for metabolic processes
Membrane Structure and Function
Membranes
Plasma Membranes
control the exchange of materials with cell surroundings
Selectively permeable
transport proteins control passage
phospholipids
most abundant lipid in the plasma membrane
amphipathic
Fluid Mosaic Model
protein molecules flow around bilayer of phosholipids, proteins are not randomly distributed
main fabric of the membrane
held together by weak hydrophobic interactions
as temp. cools membranes switch from fluid to solid, temp. of solidfication depends on the type of lipids
membranes rich in unsaturated fatty acids are more fluid than unsaturated
membranes must be fluid to work properly
steroid cholesterol in animal cells
at warm temp. it restrains movement of phospholipids
at cool temp. maintains fluidity
Proteins
determine most of the membranes functiion
2 types
Peripheral Proteins
bound to surface of the membrane
Integral Proteins
penetrate hydrophobic core
Transmembrane proteins
span the membrane
proteins built into membrane play key roles in transport regulation
Transport proteins
Allow passage of hydrophilic substances across membrane
Channel proteins
contain a a hydrophilic tunnel used by certain molecules or ions
aquaporins
facilitate the passage of water
Carrier proteins
bind and modify molecules to pass them through membrane
Cell-surface membrane Functions
Cell to cell recognition
Cells can recognize each other by binding to molecules that often contain carbohydrates
Membrane carbs may be covalently bonded to lipids or proteins
Lipids
Form Glycolipids
Protein(More common)
Form Glycoproteins
intercellular joining
Signal transduction
attachment to the cytoskeleton and ECM
Enzymatic activity
Transport
Lipid bi-layer
hydrophobic molecules
dissolve in lipid bilayer and pass easily
hydrophilic molecules
do not cross this membrane easily
Types of Transport
Passive
Diffusion
even spreading of molecules in an available space until equilibrium is achieved
diffusion is Down the concentration gradient
Osmosis
water diffusion across a membrane
Tonicity
ability to cause a cell to gain or lose water
Isotonic
a plant cell in an isotonic environment
Flaccid
Hypotonic
A plant cell in a hypotonic solution
Turgid(firm)
Hypertonic
plant cells lose water
Plasmolysis
Osmoregulation
an organisms water balance system
Facilitated Diffusion
Channel protein
tunnels that allow specific molecules across
require transport proteins
Carrier Protein
slightly modifies molecule to allow passage
Active
Types of Active Transport
Sodium/Potassium Pump
sodium is pumped against its concentration gradient
Co-transport
Symport
2 substances moving in the same direction across a membrane
Antiport
2 substances moving in opposite directions across a membrane
Bulk Transport
Moving a large molecule or a large amount of molecules
Endocytosis
Engulfing of a molecule to be taken into the cell to be digested or used
Pinocytosis(Cell drinking)
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Receptor-mediated endocytosis
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Phagocytosis(Cell eating)
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Exocytosis
molecules carried by a vesicle to be exported from the cell
Requires ATP
movement against concentration gradient
all proteins involved are carrier proteins
Membrane Potential
Voltage across a membrane
created by a difference in distribution of ions across a membrane
Cytoplasmic side = Negative
Extracellular side= Positive
Electrochemical gradient
drive diffusion of ions across a membrane
chemical force
ion concentration gradient
electrical force
effect of membrane potential on the ions movement
Electrogenic Pump
transport protein that generates voltage across a membrane
sodium potassium pump(animals)
proton pump(plants,fungi,& bacteria)
help store energy that can be used for cellular work