Cells
Every organism is made up of a cell or many cells
Humans have ~ 100 TRILLION cells each!
History
1660’s
• Microscopes developed
• Allowed for the observation of cells for the first time
• Robert Hooke examined cork under the microscope
• Saw a honeycomb – called them cellulae (latin for small rooms)
1830’s
• Matthias Schleiden and Theodor Schwann examined plant and animal tissues under the
microscope
• From this OBSERVATION, came up with the HYPOTHESIS that all living organisms are
made up of cells
Cell Properties
1. Import Raw materials
2. Ability to produce energy
3. Synthesize macromolecules (carbohydrates, proteins, lipids)
4. Organized pattern of growth
5. Respond to stimuli
6. Communication
7. Reproduction
Plasma Membrane
• All cells are surrounded by a semi
permeable plasma membrane
• Membrane is composed of a
phospholipid bilayer
• Phosphate group attached to a pair of
lipid tails
• Phosphate group is hydrophillic
• Lipid tails are hydrophobic
Prokayrotic Cells
• Single celled organisms
• Bacteria
• No membrane bound nucleus
• Cell wall on outside of cell membrane
•
Most primitive of cell types
Eukaryotic Cells
• Membrane bound organelles
• DNA located in membrane bound nucleus
• Possess subcellular organelles
Nucleus
• Command center
• Surrounded by nuclear membrane
• Nuclear ores in this membrane allow for transport between nucleus and cytoplasm of cell
• Chromosomes located here
Nucleolus
• Darker staining region of nucleus
• High concentration of RNA
• Ribosome RNA subunits synthesized here
• Subunits transported to cytoplasm via pores
• Subunits combined to form ribosomes in the cytoplasm
Ribosomes
• Protein synthesis for cell
• Consist of a large and a small subunit
• Located throughout the cell as free ribosomes or are bound to the Endoplasmic Reticulum
Endoplasmic Reticulum
• Series of channels and interconnected tubules within the cytoplasm
• Surface of E.R. is the site for carbohydrate and lipid synthesis
• Rough Endoplasmic Reticulum has ribosomes attached for synthesis of those proteins for
export
Golgi Apparatus (body)
• Flattened sacks
• Collection, packaging and distribution of materials throughout cell
• Receive materials from the ER
• Modify these contents by adding carbohydrate groups if warranted
• Often located near the nucleus
• Cisternae are special folds at the ends of golgi bodies
• Vesicles are formed by pinching off at the cisternae
• Vesicles will go to different areas of the cell or to the plasma membrane for extracellular
transport
• Vesicles can fuse with the plasma membrane to dump their contents to the outside of the cell
Lysosomes
• Vesicles which contain enzymes that break down macromolecules
• Fuse with endocytotic vesicles to break down what the cell engulfs
Peroxisomes
• Smaller vessicles than lysosomes
• Eukaryotic cell detoxification organelles
• Enzymes are received directly from free ribosomes
• Enzymes here also convert fats into carbohydrates
Mitochondria
• Energy production for the cell
• Oxidative metabolism occurs here
• ATP produced here
• Double membrane organelle – has both an outer membrane and an inner folded membrane
• Contains its own DNA separate from the nucleus
• Folded internal membrane called CRISTAE
• Cristae provide additional surface area for reactions to take place
• Filled with a fluid matrix
Centrioles
• Each cell contains a single pair
• These direct the assembly of microtubules which provide structural support for the cell
• Involved in cell division
Chloroplasts
• Found in plants and algae
• Capture energy from the sun
• Larger than mitochondira
• Inner membrane folded to form closed vesicles called Thylakoids
• Photosynthesis occurs in the thylakoids
• Thylakoids are stacked to form granna
• Fluid stroma fills the chloroplast
• Have their own DNA separate from the nucleus
Cell Mobility / Motility
• Cilia and Flagella
• Organization of microtubules for locomotion
• Cilia are short and numerous
• Create movement by beating in a coordinated manner
• Flagella are long and few in number
• Create movement by whipping action
Plants ONLY
• Central Vacuole
• Filled with water and other molecules
• Functions as storage and controls surface to volume ratio of cell
• Can increase the surface area by filling the central vacuole with fluid
•
Cell Wall
• Protection and support of plant cell
• Made of fibers and cellulose
• Strong and rigid
Diffusion
• Molecules by random motion will move from an area of higher concentration to an area of
lower concentration
• Passive process – requires no expenditure of energy
Osmosis
• Specifically the diffusion of water through a semi-permeable membrane
• Water will move from an area of high water concentration to an area of low water
concentration
Solute vs Solvent
• A solute is dissolved into a solvent
• In a solution there will be more solvent molecules than solute molecules
• Example – salt water; Solute is Salt, Solvent is Water
Semipermeable Membrane
• Cell wants to keep some things in and keep other things out
• Passive Diffusion
o Channels in the cell membrane function as gate keepers by their size
o Allow only molecules smaller than the pore size to pass through
o Molecules will travel down their concentration gradient ie from high concentration to
lower concentration
•
Facilitated diffusion
o Relies upon a carrier protein to bind to the molecule to help it cross the membrane
o Molecule still traveling down its concentration gradient
Active Transport
• Requires the expenditure of energy
• Often transporting molecules against their concentration gradient
• Channels are opened or closed in response to cellular signals
• Example – Na / K pump
• Cell pumps Na out of the cell while pumping K into the cell
• Creates a concentration gradient which is used by the cell to bring other molecules into the
cell
• Endocytosis
o Infolding of the membrane to create a membrane bound vesicle containing the target
o Phagocytosis – cell eating – large invagination
o Pinocytosis – cell drinking – small invagination
•
Exocytosis
o Extracellular transportation
o Vesicle fuses with the membrane and releases contents to the extracellular space
ATP – Adenosine Tri-Phosphate
• Energy currency of all cells
• Used for all active processes
• Energy stored in the bonds between the phosphate molecules
• Break the bond between P2 and P3 releases the most energy
•
•
Couple the hydrolysis of ATP with energy requiring reactions
Utilize the energy released by ATP hydrolysis to ‘run’ the energy requiring reactions
ATP Æ ADP + Pi + Energy
How is ATP made??
Glycolysis Æ Krebs Cycle Æ Electron Transport Chain
Glycolysis
• Occurs in the cytoplasm
• Split glucose into 2
pyruvate molecules
• Requires 2 ATP to get
started
• Generates 4 ATP
• NET ATP GAINED = 2
Krebs Cycle
• Pyruvate is transported into the
matrix of the mitochondria
• The Krebs cycle is a series of
chemical reactions which
sequentially strip electrons
from the pyruvate
• Electrons are given to the
electron carriers NAD and
FAD
• Electrons will be taken to the
Electron Transport Chain
• For each original glucose
molecule 2 ATP are produced
here
• Carbon dioxide is also
produced here
Electron Transport Chain
• Located on the Cristae of the mitochondria
• NAD and FAD bring electrons here from the Krebs cycle
• Electrons travel down the chain of special proteins releasing their energy along the way
• Oxygen is the final electron acceptor
This cellular metabolism of the krebs cycle and the electron transport chain is why we need O2
and produce CO2.
What about plants?
Plants use photosynthesis
• Capture energy from the sun (or other light) and convert it to ATP
• Use this ATP to make glucose
6CO2 + 12 H2O + Light Energy Æ C6H12O6 + 6H2O + 6O2
How do plants capture energy from light?
Why are plants green?
Why do leaves change color in the fall?
Special Pigments!
• Chloroplasts contain special molecules
called pigments
• Pigments have electrons which can use
light energy to jump to a higher orbit
• Energy is released when the electron falls
back to its original orbit
• Each pigment has a specific wavelength of
light its electrons respond to
• White light is made up of light
wavelengths ranging from 400-740
nanometers
• Chlorophyll absorbs all wavelengths
EXCEPT 500-600
• Chlorophyll reflects wavelengths 500-600
nm
• Our eyes see the reflected light which is green
• Carotenoids absorb 500-600 nm but reflect all others
When chlorophyll is abundant, we do not see the reflected light from the carotenoids because
those wavelengths are absorbed by the chlorophyll.
When chlorophyll production shuts down in response to the shorter days of fall, the carotenoid
pigment reflected wavelengths are now visible to our eyes resulting in the colors of fall leaves.
Photosynthesis occurs in 2 stages
• Light Reactions
o Require light and water
o Produce ATP and O2
o Take place on the thylakoid membranes of the chloroplast
o Light energy is used to make ATP
•
Dark Reactions
o Occur in the stroma of the
chloroplast
o Use the ATP produced during
the light reactions to make
glucose from CO2
How do more cells get made?
Need to make two of everything in the cell
including DNA
DNA Synthesis
• DNA is a double stranded helix
• Each strand is said to be complimentary
to the other
• The 4 bases pair in specific couples
• Adenine (A) only pairs with Thymine
(T)
• Guanine (G) only pairs with Cytosine (C)
•
•
•
This is called complimentary base pairing
Enzyme DNA Polymerase synthesizes DNA
Replication is semi conservative - Each daughter double helix will consist of one original and
one new strand of DNA
Semi Conservative Replication
Cell Cycle
All cells have a life cycle
Checkpoints throughout the cell cycle ensure the cell divides in an appropriate manner
G1
Gap 1 - Resting cell
G1 Check point decides if cell should
divide
S
G2
Synthesis phase when DNA is duplicated
(synthesized)
Gap 2 – Make more organelles
G2 Check point DNA duplication assessed
Mitosis Check point assesses the success
of cell division
M
Cancer is uncontrolled cell division
• A cell no longer responds to its normal cell cycle
• Results from damage to its DNA
Protein p53 “The guardian angel”
• Monitors the integrity of DNA
• Signals repair enzymes to address damaged DNA
• Tags cells for destruction if their DNA is damaged beyond repair
• Without this protein, damaged cells could proliferate leading to cancer
Mitosis – Cell Division
• Make two EXACT daughter cells from one parental cell
• Divided into 4 separate stages
• DNA is already duplicated when mitosis begins
Prophase
• Nuclear membrane breaks down
• Chromosomes condense and coil tightly around histone
proteins
• Centrioles duplicate and form the spindle apparatus of
microtubules
Metaphase
• Chromosomes aligned at the midline of the cell by the
spindle apparatus
• The duplicated chromosome pairs now duplicate their
centromeres
Anaphase
• Chromosome pairs pulled apart toward opposite poles of
cell by their centromeres
Telophase / Cytokinesis
• Chromosomes begin to unwind as the nuclear membrane is
reformed
• Cytoplasm is divided into the two cells by the pinching of
the cell membrane to create two separate cells
Meiosis
• For GAMETE (sex cell) production ONLY
• Most organisms live as diploid creatures meaning possessing two copies of each
chromosome
• Most organisms utilize sexual reproduction
• In order to maintain proper chromosome number, the DNA must be reduced by 50% in the
gametes
What would happen to the amount of DNA and the chromosome number if it were not reduced
by 50%?
Each parent produces Haploid gametes
Meiosis is how diploid organisms produce haploid cells
Prophase I
• Cross over between homologous pairs of
chromosomes
• Centrioles duplicate
• Spindle apparatus forms
Metaphase I
• Pairs of duplicated chromosomes line up at
midline
Anaphase I
• Individual pairs of duplicated chromosomes
pulled to opposite poles of cell
Telophase I
• Cleavage furrow separates cell into two
Prophase II
• Centrioles duplicate
• Spindle apparatus reforms
Metaphase II
• Chromosome pairs line up at midline
Anaphase II
• Sister chromatids now separated and pulled
toward opposite poles of cell
• At this point DNA is reduced by 50%
Telophase II
• Cleavage furrow forms
• Results in a total of 4 haploid daughter cells
from 1 parental cell
• Each one is genetically unique due to crossing
over in Prophase I