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TRANSCRIPT
Chapter 4Cell Structure and Function
Names of the 17th Century
Leeuwenhoek- skilled lensmaker, looked at protists, bacteria, “small animalcules” in tooth tartar
Hooke- saw compartments in cork, called “cellulae” for small rooms, now termed cell
1800’s
By the 1820s lenses were sharper
Brown- identified plant cell nucleus
Schleiden- wondered how cells develop in plants
Schwann- cells are in animal tissue as well and have an individual life of own
Virchow- every cell comes from a pre-existing cell
Invisible to the naked eye
Hooke’s view
Today’s Microscopes
The Cell Theory
1. Organisms have one or more cells.
2. The cell is the smallest unit of an organism that still displays properties of life.
3. Life arises from growth and division of a single cell.
Cells and Structure
bacteria and archaeans are prokaryotes: simplest cells, no nucleus or membrane bound organelles
eukaryotes have a nucleus and other membrane bound organelles
Properties of Life Displayed
capacity for metabolism
response to the environment
growth and reproduction
all cells differ in size, shape and activity
Structures In All Cells
plasma membrane
DNA
cytoplasm
ribosomes
Plant and Animal Cell
DNA
found in nucleus in eukaryotes, surrounded by a nuclear membrane
found in a nucleoid region in prokaryotes, there is no membrane enclosing this area of the cytoplasm
Cytoplasm
consists of the space between the plasma membrane and the region of DNA
semifluid
suspends organelles to perform tasks such as protein synthesis and energy conversion
cytoplasm
Cell Membrane
defines cell, separates from surroundings, allows certain things through such as H2O, CO2, O2 freely, others need help such as nutrients and ions
lipid bilayer is basis of plasma membrane and other membranes in cell
oily, prevents passage of water soluble sub.
Bilayer Structure
Cell Membrane
membranes inside cell act as channels and sacs to transport, synthesize, modify, store, digest (golgi, ER, vacuole, lysosome)
proteins embedded in lipid bilayer or on surface are responsible for many functions such as acting as channels or pumps for substances to cross, receptors for hormones, and other molecular cell needs
Cell Membrane Mosaic
cytoplasm
lipid bilayer
recognition protein
receptor protein
protein pump
protein channel protein pump
extracellular environment
Cell Size
largest cell is yolk of bird egg, watermelon tissue cells, amphibian and fish eggs
most of volume is nutrients and not much activity
if cell must perform a task, it must be tiny
Cell Size
key is surface area to volume ratio- this keeps the cell from growing too large
volume increases faster than surface area, and then there is not enough surface to get substances in and out fast enough to support the increased volume
cells that cannot support metabolic activity die
Solutions
larger cells can be long and thin, or have many folds in the membrane to increase the surface area (frilly)
muscle cells and nerve cells are long and thin
SA:V
Prokaryotic Cells
smallest cells living in a variety of environments
2 domains: 1. bacteria 2. archaea
similar in size and appearance
differ in AA sequence used to start polypeptide chain (archaea is same as eukaryotes) and protein that helps in folding DNA, called histone
Cell Wall
cell wall outside plasma membrane gives rigidity, shape
usually coated with sticky carbohydrate to help adhere to surfaces (teeth, intestines)
cell wall is permeable
Extracellular Structures
many have flagella, often 1 or more, made of motor like structure (not microtubules as in eukaryotes)
can also have pili, filiments to help cling to surface
special sex pili reels in another cell and trade of genetic material follows
Bacterial Flagella
Inside the Prokaryotes plasma membrane has built in molecules for certain
jobs such as protein channels, transporters, energy conversion
cytoplasm has ribosomes to build proteins
nucleoid region of DNA, one circular piece of DNA called bacterial chromosome
some have plasmids, small circles of DNA with only a
E. Coli DNA
flagellum
pillus
nucleoid
Cyanobacteria
part of membrane folded into cell with pigments and molecules embedded for photosynthesis-- ancestor of chloroplast?
Eukaryotic Cells“true nucleus”
organelles for certain functions with enclosed microenvironment to control substances entering and leaving
mitochondria and chloroplasts hold H ions for generation of ATP
lysosome has enzymes for digestion
Interaction of Organelles
secretory pathway: route for proteins from ribosomes ER golgi plasma membrane release
endocytic pathway: moves molecules into cell- vesicles pinch off of cell membrane to transport a substance
Plant Cell
Animal Cell
The Nucleus
2 main functions: 1. keeps DNA away from cytoplasmic rxns. 2. controls substances going in and out of nucleus
contains nucleolus: site of ribosome construction
at least one
mass of proteins and genes coding for ribosomal RNA
Nuclear Envelope
double lipid bilayer (2 of them)
outer merges with ER, has ribosomes on it
inner has attached proteins that anchor DNA and keep it organized
proteins spanning both layers are receptors, transporters
Nuclear Envelope
DNA
codes for proteins, not visible when cell is not dividing, condense and coil when dividing
nucleoplasm
chromatinnucleolusnuclear envelope
Endomembrane SystemConsists of A. ER B. golgi body C. vesicles
ER: flattened channels folded repeatedly where proteins modified, lipids assembled, vesicles pinch off and deliver to golgi, continuous with nuclear membrane
rough: ribosomes attached
smooth: no ribosomes, makes lipids for cell membrane
Endomembrane System
sarcoplasmic reticulum: type of smooth ER that functions in muscle contraction
golgi bodies: membrane folded on itself and stacked, attaches sugar and lipid side chains to proteins from ER and sends finished product out in a vesicle
Endomembrane System
Membraneous Sacs
exocytic vesicles: release substances to outside cell
endocytic vesicles: bring molecules into cell
lysosomes: bud from golgi, store digestive enzymes, will fuse with another vesicle to activate enzymes
peroxisomes: enzymes to digest fatty acids, amino acids, liver and kidney peroxisomes degrade alcohol
Membraneous Sacs
vacuole: form from fused vesicles, storage
plant central vacuole is large, fluid filled, stores amino acids, sugars, wastes, will expand as fills and force cell wall to expand, 50-90% of cell interior in mature cell
MitochondriaATP formation in aerobic respiration
have own DNA and divide on own, some have ribosomes
outer and inner membranes creates 2 sections
inner membrane is highly folded, H ions flow through and ATP is generated through proteins embedded in membrane
H ions stocked in outer compartment and flow to inner
Mitochondriahigh energy cells have thousands, ex. liver, muscle
inner compartment
outer compartment
inner membrane
outer membrane
Specialized Plant Organelles
plastids: function in storage or photosynthesis
chloroplasts
chromoplasts
amyloplasts
Chloroplastsphotosynthesis takes place here
2 outer membranes
stroma is semifluid inside
third membrane in stroma, highly folded, called thylakoid, forms stacks called grana
photosynthesis takes place in thylakoid where chlorophyll is located
Chloroplasts
ATP, NADPH formed, energy used to build sugars
stroma
thylakoid outer membranes
Chromoplasts
no chlorophyll but carotenoids (reds, yellows) of autumn leaves, fruits, roots, vegetables, attract animals
Amyloplasts
pigment free, store starch
find many in stem, tubers (underground stems, ex. potatoes), seeds
Cell Surface Specializations
Cell wall: wraps around plasma membrane of many protists, fungi, and plants
primary: made of secreted polysaccharide pectin to glue cells together, thin and pliable
secondary: inner surface of primary wall, stronger
Cell Wall
primary
secondary layers
Cell Junctions
structures that allow for cells to communicate or adhere to one another
Animals: 3 types
tight
adhering
gap
Animal Cell Junctions
tight: seals so no fluid leaks between cells, find in stomach, internal cavities, linings of outer surfaces
adhering: link cells that are stretched such as skin, heart, organs that stretch
gap: cytoplasm of cells is directly connected so open channel for movement of fluids such as in heart muscle cell
Animal Cell Junctions
Plant Cell Junction
Plasmodesmata: connect cytoplasm for rapid movement of substances (like gap junction in animals)
Cytoskeleton
structural framework of eukaryotic cells
basis for shape and internal organization
allows organelle movement inside cell
made of protein filaments that are permanent or formed when needed
Microtubules
largest cytoskeletal element that keeps organelles in place or moves them, ex. spindle fibers for chromosome movement in mitosis and meiosis
hollow cylinders of tubulin protein each oriented so “plus” end faces growth direction and “negative” end is anchored in patches of centrosomes, areas of microtubule origin
Microfilaments
thinnest of elements
2 helically coiled chains of actin protein monomers
often in bundles, ex. cell cortex, a bundled mesh reinforcing cell shape and aids in pinching cell in mitosis division
can anchor membrane proteins
Structure of filaments
microtubule microfilament intermediate filament
Accessory Proteins
kinesin and myosin are motor proteins that move with inputs of ATP and can help move cell parts such as a vesicle along a microtubule
Intermediate Filamentsmedium size, found in animal cells only, strengthen
and maintain cell shape and parts
6 known groups
lamins: weaved mesh, reinforces nucleus and anchors actin and myosin filaments to aid in contraction of muscle cells
desmins and vimentins: hold contractile units in place
cytokeratins: reinforce nail, claw, horn, hair cells
Intermediate Filaments
Prokaryotes
no well developed cytoskeleton, but do have reinforcing filaments found in some bacteria, made of protein subunits similar to tubulin and actin, with similar assembly pattern
How Cells Movemotor proteins: microtubules and microfilaments act as
roads for motor proteins to travel, fueled by ATP
kinesin, dynein, myosin
chloroplasts, chromosomes, muscle cell all are moved due to motor proteins
vesicles moved a certain distance before handed off to another motor protein
Motor Protein
vesicle
motor protein
filament
Cilia, Flagella, False Feet
structures that are extensions of the plasma membrane used for movement
cilia are shorter extensions covering some protists, and animal cells such as lung cells
flagella are longer, whip-like
Structure
centrosome: anchors microtubules, gives rise to centriole which gives rise to microtubules organized in a “9 + 2” pattern
centriole acts as base of pattern, called a basal body
9 + 2 Array
9 microtubule pairs form ring around central pair, held in place by protein spokes and linker proteins along length of pairs
Cilia and Flagella
microtubules cannot be pushed further out, so motor proteins create a bending effect around the 9+2 array which bend the cilia or flagella
Pseudopods: False Feet
lobes bulge out of cell to move or engulf prey
microfilaments inside elongate and advance cell by means of motor protein and cell membrane is dragged along with them
amoeba
Cilia
Flagellum
Pseudopods
9 + 2 Array