Download Anatomy of Cells

Anatomy of Cells
History of the Cell Theory
1. Robert Hooke – 1665 – named cell
2. Leeuwenhoek – 1695 – observed living
microorganisms
3. Schwann – 1839 – all animals made of
cells
4. Schleiden – 1839 – all plants made of cells
5. Virchow – 1855 - all cells come from cells
Cell Theory
 Cells are the basic structural and functional
units of life
 Under the conditions present on Earth today
all cells come from other cells.
 Cells of multicellular organisms must stick to
solid surfaces to perform normally.
Tools of Microscopic Anatomy
Microscopy
- the history of cytology is tied to the
development of the microscope.
1. Light microscopes (pg. 70 – 71)
- pass light through the specimen
- can magnify up to about 1200x
- easy to prepare specimens and can
look at living specimens.
- resolving power – ability to
distinguish between two objects
2. Transmission Electron Microscope
- send a beam of electrons through the
specimen
- focused with magnets
- resolving power up to 100,000(+)x
- specimens have to be prepared and can’t be
alive
3. Scanning Electron Microscope
- bounce electrons off the surface of the
specimen
- gives detailed three-dimensional images of
the surface of the specimen
Cell Fragmentation
 Used to study cell physiology
 Separate the cell into various components and
study what each component does.
Radioactive Isotope Labeling
 Use techniques to get radioactive isotopes of
various elements into a cell and then study
how the cell uses that element.
Functional Anatomy of Cells
Basic Cell Structures
1. Plasma Membrane – separates the cell
from its surrounding environment
2. Cytoplasm – thick gel-like substance
inside the cell housing numerous
organelles suspended in water cytosol;
each type of organelle is suited to a
particular function.
3. Nucleus – large membranous structure
near the center of the cell
Why are cells small?
1. Surface-to-volume ratio
- cells exchange materials with their
environment through the cell membrane at
their surface
- as structures get larger, their volume
increases at a faster rate than their surface
area
- eventually there is not enough surface area
for the needed materials to enter or for waste
materials to exit the cell
2. Less distance for materials to move within the
cell
- increases probability of molecular collisions
and thus of reactions happening
- within the cell the organelles create even
smaller compartments for reactions to happen
in
3. Finite amount of DNA to control the
metabolism of the cell.
- DNA only can control the production of
proteins sufficient for a small area
Cell Membranes
 All of the membranes of the cell have similar
structure.
Plasma Membrane
 Fluid Mosaic Model – developed by Singer and
Nicolson
 Molecules are arranged in a sheet
 Molecules can move laterally in the membrane
 Molecules are held together by chemical attractions
between them and their interactions with water.
 Primary structure is a double layer of phospholipid
molecules
 Phosphate heads are hydrophilic; tails are
hydrophobic
 Cholesterol molecules within the membrane
help it function at body temperatures.
 Because the hydrophobic tails make-up most
of the membrane, water soluble materials can’t
pass through the membrane.
 Channel proteins which are embedded in the
membrane help control movement of materials
into and out of the cell
 Glycoproteins have carbohydrates attached
and serve as cell surface identifiers
 Receptor proteins react to specific chemicals
and cause changes within the cell.
 Overall, the plasma membrane is selectively
permeable.
Movement through the Membrane
Passive Transport Processes
 Do not require energy expenditure by the cell
1. Diffusion
- movement of particles from an area of high
concentration to an area of low concentration
down a concentration gradient.
- continues until equilibrium is reached
- membrane channels are pores through
which specific ions or small water-soluble
molecules can pass
- gases also move by diffusion
2.
Carrier-facilitated diffusion
- movement through carrier proteins along the
concentration gradient
- rate is dependent on concentration gradient and
availability of carrier molecules
3. Osmosis
- diffusion of water through a selectively permeable
membrane
- water moves down it’s concentration gradient – this
often means it is moving toward higher salt
concentrations
- Osmotic Pressure – water pressure that develops as a
result of osmosis
- healthy cells are normally in an environment where
the net movement of water is 0.
- Tonicity – ability of a solution to move water in/out of
a cell and change its shape
a. Isotonic – osmotic pressure is = inside and outside
b. Hypertonic – osmotic pressure is greater than within
the cell – water moves out of cell causing crenation
c. Hypotonic – osmotic pressure is less than within the
cell – water moves into the cell causing lysis.
4. Dialysis
- form of diffusion in which the selectively
permeable membrane separates large and small
solute particles
5. Filtration
- passage of water and permeable solutes through a
membrane by the force of hydrostatic pressure
- small solutes pass down a hydrostatic pressure
gradient
- separates large and small solutes
- happens most often in the capillaries
- kidney function is dependent on blood pressure
Active Transport Processes

1.
cell uses metabolic energy to move materials
Active Transport
- carrier-mediated process that moves substances
against their concentration gradients
- opposite of diffusion
- substances are moved by pumps which use ATP to
change shape and move their cargos
- carrier proteins bind to cargo, change shape, and
release the cargo
2. Endocytosis and Exocytosis
- allow things to enter and leave a cell without actually
passing through the plasma membrane.
A. Endocytosis – plasma membrane traps some
extracellular material and moves it to the interior in a
vesicle.
- Phagocytosis – large particles are engulfed within
a vesicle that then fuses with lysosomes to digest
particles
- Pinocytosis – fluid and the substances dissolved
in it enter the cell
3. Exocytosis
- process that cells use to expel large molecules,
notably proteins for export
- large molecules are first enclosed in membranous
vesicles which then fuse with the plasma membrane
and release their contents to the environment
surrounding the cell.
- also is how the smooth endoplasmic reticulum is
able to add new material to the plasma membrane
Cytoplasm and Organelles
1.
2.
Cytoplasm
- semifluid substance that occupies most of the cell
interior = cytosol
- organelles are suspended in the cytoplasm and
attached to the cytoskeleton
- contains nutrients, ions, and other raw materials
important to cell functioning
- carries-out most of the properties of life
Endoplasmic Reticulum
- membranous-walled canals and flat sacs that
extend from the plasma membrane to the nucleus
- important in the synthesis, modification, and
movement of materials within the cell
A. Rough Endoplasmic Reticulum
- has ribosomes attached to its’ surface
- ribosomes make proteins which move into the
cisternae of the ER and are transported
toward the Golgi apparatus
B. Smooth Endoplasmic Reticulum
- lacks ribosomes
- transports, synthesizes, and chemically modifies
small molecules
- synthesizes certain lipids and carbohydrates and
creates membranes for use throughout the
cell
- helps in detoxification of poisons in the liver
- stores Ca++ in the muscle fibers
3.
Ribosomes
- sites of protein synthesis – where amino acids are
joined
- many are attached to Rough ER; others are free in
the cytoplasm
- composed of two nonmembranous structures which
come together once a mRNA molecule attaches to the
large subunit
- attach to the mRNA and move along it adding amino
acids as directed by the code
- subunits are composed of rRNA and protein
- attached ribosomes make proteins for export
- free ribosomes make proteins for intracellular use
Ribosomes
4. Golgi Apparatus
- series of flattened membranous sacs that modify protein products
of the rough endoplasmic reticulum
- final products are packaged in vesicles which can then be moved
to the cell membrane for export
- some of these vesicles remain in the cell as lysosomes
- can also give rise to new membrane structures for the cell
5.
6.
Lysosomes
- digestive system of the cell
- membranous sacs which pinch off the Golgi
apparatus
- contain hydrolytic enzymes which digest particles
or large molecules that enter them
- also responsible for digesting unneeded or
unhealthy cells and cell parts
Peroxisomes
- small membranous sacs which contain enzymes
that detoxify harmful substances that enter cells
- common in kidney and liver cells
Endomembrane System
7.
Mitochondria
- “power plants” of cells
- double membraned organelle with fluid between the
membranes
- lots of enzymes attached to both membranes
- enzymes catalyze oxidation reactions of cellular
respiration and capture the energy of sugars in the
bonds of ATP
- provide 95% of the cell’s energy
- contain their own ribosomes and DNA and can
replicate themselves
Nucleus
 “control center” of the cell
 Contains the chromosomes on which the genes are
located
 Fine threads called chromatin in nondividing cells
 Condense into visible chromosomes during cell division
 Nuclear membrane has two parallel membranes with
nuclear pores penetrating them
 Nuclear pores allow mRNA to leave the nucleus to go to
the cytoplasm
 Also contains the nucleolus where ribosomal subunits
are produced
Cytoskeleton


A.
Internal support framework made up of rigid, rodlike
proteins that support the cell and allow movement
and mechanisms that can move the cell or its parts
Acts as both muscle and skeleton for cell
Cell Fibers
- form a three-dimensional support framework
- support endoplasmic reticulum, mitochondria, and
free ribosomes
1. Microfilaments – smallest fibers
- cellular muscles that provide for movement
2. Intermediate filaments – form much of the support
network of the cell
3. Microtubules – maintain cell shape and move
things within the cell
B. Centrosome
- coordinates the building and breaking of microtubules
in the cell
- centrioles are located within the centrosome
- during cell division makes the mitotic spindle
C. Cell Extensions
- cytoskeleton forms projections that are covered by
the plasma membrane
1. Microvilli – increase the surface area in intestines
and other areas for better absorption
2. Cilia and Flagella – project from the surface of cells
and allow cell movement or create movement past
the cell surface
- cilia are short and numerous; flagella long
Cell Metabolism
Metabolism
- Sum of all of the chemical reactions in cells
- Nearly all reactions are catalyzed by enzymes
- Enzymes are specific in their actions as they work
based on the shape of their active site and the shape of
the substrates they work on.
- Enzymes work best under certain conditions and can
be denatured and made ineffective by changing those
conditions – temperature and pH
Catabolism
 Catabolism is the chemical reactions that break large
molecules into smaller molecules and often release
energy
 Cellular Respiration
- Process by which cells break down glucose into
carbon dioxide and water
- Releases energy stored in the sugar and transfers it
to the high energy bonds of ATP
- Three main processes:
1. glycolysis – splits glucose into two pyruvic acid
molecules
- happens in the cytoplasm and forms ATP and
molecules that enter the mitochondria
2. Citric Acid Cycle = Krebs Cycle
- happens in the matrix of the mitochondria and
breaks down the pyruvic acids from glycolysis
into CO2 and other molecules that carry protons
to the
3. Electron Transport Chain
- series of proteins embedded in the inner
membrane of the mitochondria which pass
electrons from one to another and capture their
energy in the bonds of ATP
- produce most of the ATP we use
- Oxygen is the final electron acceptor
Anabolism
- Constructive reactions in cells
- Ultimately controlled by DNA
- Genes in DNA control
production of proteins
- Gene = sequence of bases
which control production of a
polypeptide
Transcription and Translation = Protein
Synthesis
Transcription
 Making messenger RNA from one gene of
the DNA
 Base pairing rules assure that mRNA has
correct sequence (A-U; C-G)
 Codon – sequence of three bases on
mRNA that code for an amino acid – each
codon codes for a specific amino acid
 mRNA leaves nucleus through nuclear
pores and attaches to ribosome where
translation occurs
Translation
 mRNA attaches to a ribosome
 tRNA molecules bring specific amino acids to the
mRNA at the ribosome – anticodon of tRNA base pairs
with codon of mRNA which ensures that the correct
amino acid is attached to the polypeptide
 Peptide bonds join the amino acid to the growing
polypeptide chain
Enzymes then help fold the polypeptide and join it with
others to form functional proteins.
Growth and Reproduction of Cells



Growth and reproduction are fundamental
characteristics of life
Cell growth uses DNA instructions to make structural
and functional proteins needed for cell survival
Cell reproduction ensures genetic information is
passed from one generation to the next
Interphase

Normal condition of a cell

Divided into three phases
1. G1 – First Gap Phase
- cell grows to “adult” size by manufacturing
cytoplasm and organelles
- carries out normal functions
- variable length of time
- centrioles begin to replicate
- chromosomes are single-stranded
2. Synthesis – S phase
- DNA replication occurs
- semi-conservative replication – each new double
strand is made of one new strand and one
old strand
- replication is controlled by DNA polymerase
- unzips DNA and breaks H-bonds between strands
- base pairs free nucleotides to exposed
nucleotides
- doubled chromosomes are made of sister
chromatids joined at their centromere
3. G2 – Second Gap Phase
- cell is waiting and preparing to divide
Mitosis
- normal process of cell division
- every cell ends up with the same genetic information
- four phases
1. Prophase
- chromosomes condense and become visible
- nuclear membrane dissolves
- centrioles move and begin to form spindle fibers
which stretch across the cell and attach to
centromeres of chromosomes
2. Metaphase
- chromosomes are pulled and line up at the
equator of the cell
- a spindle fiber is attached to each side of the
centromere
3. Anaphase
- centromere of each chromosome has split
- each chromosome is pulled toward the nearest
pole
- forms two separate identical pools of genetic
material
4. Telophase
- DNA unravels to form chromatin
- nuclear membrane reforms
- spindle breaks down
Cytokinesis
- division of the cytoplasm