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 ADP + Pi + Energy How is ATP made??
Glycolysis Krebs Cycle 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 O 2 and produce CO 2.
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 6CO 2 + 12 H 2 O + Light Energy C 6 H 12 O 6 + 6H 2 O + 6O 2 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 O 2 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 CO 2 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 M 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 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