Test Guide Unit 2 Cells

Unit 2: Cells Cell Theory ❖ Every living thing is made of cells. ❖ The basic unit of life is the cell. ❖ Every cell comes from preexisting cells ➢ Most cells are 10-100 micrometers (μm), but others are smaller (red blood cells = 8μm) ➢ All cells have a membrane and nucleic acid. Prokaryotes vs. Eukaryotes ❖ Prokaryotes: ➢ No nucleus or membrane-bound organelles ➢ Have one circular chromosome, sometimes have plasmids ➢ Small ribosomes are present ➢ Can do anaerobic or aerobic respiration ➢ No cytoskeleton; have cell walls ➢ Unicellular and very small (1-10 μm) ❖ Eukaryotes: ➢ Have nucleus and membrane-bound organelles ➢ Have linear chromosomes (46 in human nucleus); no plasmids ➢ Large ribosomes are present ➢ Have cytoskeleton; most don’t have cell walls (except plants and protists) ➢ Sometimes unicellular, but usually multicellular and specialized; relatively large (10-100 μm) ❖ Theory of endosymbiosis - formation of first eukaryotic cells (~2.4 billion years ago) when smaller prokaryotes were phagocytosed by larger ones and became a part of them permanently ❖ Form relates to function when it comes to cells, and different types of cells have different functions and shapes. However, they still have (mostly) the same organelles. Parts of the cell ❖ Nucleus ➢ Is where genes are located (in the form of a chromatin network) ■ Chromatin is DNA wrapped around histones, or basic proteins, and it condenses to form chromosomes ➢ Has a nuclear membrane that separates nucleus from cytoplasm ■ Contains pores that allow for transport out of the nucleus ❖ Nucleolus ➢ Usually 1-2 are located inside nucleus of non-dividing cell ➢ Does not have a surrounding membrane ➢ Is where ribosomes are made ➢ Made of chromatin + ribosomes that are being created ❖ Ribosome ➢ Is where proteins are made ➢ Consists of rRNA (ribosomal RNA) and protein ➢ Can be free in cytoplasm or on endoplasmic reticulum ❖ Endoplasmic Reticulum (ER) ➢ Membrane system in the cytoplasm ➢ Two types of ER: ■ Rough ER ● has ribosomes on surface ● makes proteins + transports them ■ Smooth ER ● makes lipids (ex. steroid hormones) ● connects rough ER and Golgi apparatus ● metabolizes glycogen and detoxifies cell ❖ Golgi Apparatus ➢ System of flattened membrane pouches ➢ Responsible for modification, storage, and packaging (into vesicles) of proteins/lipids ■ These proteins/lipids can then be transported to other locations ❖ Vacuole ➢ Space without cytoplasm surrounded by a membrane ➢ Responsible for storage ➢ Example: contractile vacuoles ➢ *vesicles are very small vacuoles ❖ Lysosome ➢ Membrane-bound sacs filled with digestive enzymes ➢ Responsible for intracellular digestion (digestion within cell) ➢ Recycles cell parts + allows for apoptosis (programmed cell death) ❖ Mitochondria ➢ Where cell respiration happens in all cells ➢ Have a double membrane and inner membranes that are folded (cristae) ➢ Have their own unique DNA ❖ Plastids ➢ Have double membrane; only in plants/algae ➢ Types of plastids: ■ Chloroplasts ● Where photosynthesis occurs ● Have chlorophyll (which makes them green) ● Inner membrane is folded to create grana ● Have their own DNA ■ Leucoplasts ● Responsible for storing starch ● Colorless and are in roots/tubers ■ Chromoplasts ● Responsible for storage of carotenoids (which make carrots, tomatoes, and other plants red/orange/yellow) ❖ Cytoskeleton ➢ Made of protein filaments that allow the cell to move/maintain shape ➢ Two types of cytoskeletal elements: ■ Microtubules - thick tubes made of tubulin; make spindle fibers, flagella, cilia ■ Microfilaments - made of actin; maintains cell’s shape ● Examples of functions: ◆ cleavage furrow when cell divides ◆ pseudopods in amoeba ◆ movement of skeletal muscles ❖ Cilia/Flagella ➢ Consists of microtubules (9 pairs around 2 central ones) ➢ Cilia = short, flagella = long ❖ Centrioles/Centrosomes ➢ Made of 9 microtubule triplets ➢ Responsible for organizing spindle fibers when cell divides ➢ Only in animal cells ➢ 2 centrioles = 1 centrosome; centrioles are perpendicular to each other ❖ Cytoplasm & Cytosol ➢ cytoplasm - area from outside of nucleus to plasma membrane (includes organelles and cytoskeleton) ➢ cytosol - only the liquid part of cytoplasm ❖ Plasma Membrane ➢ Selectively permeable membrane made of phospholipid bilayer ➢ Includes proteins, cholesterol, and carbohydrate chains attached to membrane ❖ Cell Wall ➢ Only in plants, algae, and fungi (plants, algae = cellulose walls; fungi = chitin walls) ➢ middle lamella - layer that attaches 2 plant cells after cell division Plant vs. animal cells ❖ Plant cells: ➢ No centrioles/centrosomes or lysosomes ➢ Have chloroplasts + other plastids ➢ Large vacuole in center of cell ➢ Have cell wall and plasma membrane ❖ Animal cells: ➢ Have centrioles/centrosomes and lysosomes ➢ No chloroplasts + other plastids ➢ Usually only small vacuoles ➢ Only have plasma membrane Transport in/out of a cell ❖ Passive Transport ➢ When molecules move from high → low concentration without using energy ➢ Examples of passive transport: ■ Simple diffusion - direct movement of molecules from high → low concentration; steeper gradient = faster diffusion ● Ex. oxygen diffusion in human lungs (specifically in alveoli) ■ Facilitated diffusion - requires protein channels to move certain substances through a membrane ■ Osmosis - when water diffuses through a membrane to a place with more solute (hypertonic) ● Cell in hypertonic solution - water moves from cell to solution ◆ Cell shrinks (plasmolysis) ● Cell in hypotonic solution - water moves into cell from solution ◆ Animal cell bursts (lyses) ◆ Plant cell swells (becomes turgid); plants lose turgor pressure/wilt when not watered ● Cell in isotonic solution - water moves in + out of cell at same rate ◆ Cell doesn’t shrink or swell ❖ Active Transport ➢ When molecules move against the concentration gradient using energy (ATP) ➢ Types of active transport: ■ Exocytosis - when a cell releases molecules using energy (ex. Nerve cells release neurotransmitters into synapses through vesicles) ■ Endocytosis - when cells form new vesicles by absorbing molecules; the three types are: ● Phagocytosis - when large particles/tiny organisms are engulfed by pseudopods ● Pinocytosis - when small dissolved molecules are absorbed (cell drinking) ● Receptor-mediated endocytosis - when specific substances bind to ligands (receptors on the membrane) + are enclosed in a vesicle ■ Sodium-potassium pump - protein pump in nerve cells that generates an ion gradient Cell cycle ❖ Affected by signals (either internal or external), which control 3 checkpoints that strictly regulate cell division ❖ Cell cycle stages: G1, S, G2, mitosis, cytokinesis ➢ Some cells (ex. neurons) remain in G0 / don’t divide. ❖ Interphase (>90% of cell’s life) ➢ In G1 phase, cell grows and prepares for DNA replication ■ G1 checkpoint ➢ In S phase, DNA is synthesized ■ S checkpoint ➢ In G2 phase, organelles + other cellular components are produced ■ G2 checkpoint ❖ Mitosis (division of nucleus) - for growth + repair ➢ Prophase ■ Chromosomes are visible ■ Nucleoli disappear ■ Spindle fibers begin forming ■ Centrioles start moving to poles ➢ Metaphase ■ Chromosomes line up on metaphase plate (single file) ■ Centrosomes at poles opposite to each other ■ Spindle fibers fully formed (connected to centromeres of chromosomes) ➢ Anaphase ■ Sister chromatids are pulled apart by spindle fibers ➢ Telophase ■ Chromosomes move to opposite ends of cell ■ Nuclear membrane forms ■ Chromosomes start to unravel back into chromatin ❖ Cytokinesis (division of cytoplasm) ➢ Animal cells - cleavage furrow forms and daughter cells separate ➢ Plant cells - cell plate forms in middle, cells don’t separate; middle lamella keeps cells together Meiosis ❖ Cell division that produces haploid gametes (sex cells) ❖ Stages of meiosis: ➢ Meiosis I (reduction division) ■ Synapsis (pairing of homologous chromosomes) and crossing-over (homologous chromosomes swap genetic material) occur ■ Homologous pairs separate ■ Homologous chromosomes randomly line up in middle + separate independently of each other ■ Every gamete is genetically different ➢ Meiosis II ■ Sister chromatids separate ■ # of chromosomes stays haploid ■ Results in 4 genetically different daughter cells from one cell Cellular Respiration ❖ Process where cells break down glucose and transfer its energy to molecules of ATP ➢ *ATP (adenosine triphosphate) - made of adenosine (adenine + ribose) and 3 phosphate groups; stores lots of energy ❖ Mitochondria structure ➢ 2 membranes: ■ Outer membrane ■ Inner cristae membrane (where electron transport chain occurs) ● Outer compartment ● Matrix - where Krebs cycle occurs ❖ Two types of cell respiration ➢ Aerobic respiration ■ Has anaerobic phase (glycolysis) + aerobic phase (citric acid cycle/Krebs cycle + oxidative phosphorylation/chemiosmosis) ■ Glycolysis ● Occurs in cytoplasm + controlled by enzymes ● 2 ATP needed to start glycolysis ● 1 glucose + 2 ATP → 2 pyruvate + 4 ATP + 2 NADH ◆ Net gain = 2 ATP ■ Citric acid cycle/Krebs cycle ● Pyruvate from glycolysis + coenzyme A = Acetyl-CoA, which enters Krebs cycle ● Occurs in matrix of mitochondria ● 1 turn of Krebs cycle = 1 ATP + 1 FADH2 + 3 NADH ◆ By-product: carbon dioxide ◆ NADH produces 3 ATP, FADH produces 2 ATP ➢ Oxidized forms: NAD+ and FAD+ ➢ Reduced forms: NADH and FADH2 ■ Electron Transport Chain (ETC) ● In cristae membranes (mitochondria) ● Produces most ATP in aerobic cell respiration ● FADH2 + NADH transport energized electrons from Krebs cycle to ETCs ● Energy from electrons is used to pump protons (H+) from inner matrix to outer compartment through active transport ◆ Proton gradient is formed and has lots of potential energy ◆ H+ can only flow down concentration gradient through ATP synthase channels, powering production of ATP from ADP + phosphate (chemiosmosis/oxidative phosphorylation) ● Oxygen helps electrons move through ETC + is final electron/proton acceptor ◆ Forms water as waste product by combining with protons + electrons ➢ Anaerobic respiration ■ Does not require oxygen; evolved when no oxygen on Earth ■ Glycolysis → *Fermentation ● *Can be lactic acid fermentation (used by skeletal muscles) or alcohol fermentation (used by yeast) Photosynthesis ❖ Series of reactions where plants use energy from light to create glucose ➢ Formula: 6CO2 + 12H2O → C6H12O6 + 6H2O + 6O2 ❖ Photosynthesis is a reduction reaction (carbon in CO2 gains electrons from hydrogen in H2O) ❖ Photosynthetic pigments ➢ Chlorophyll a and b - absorbs red-violet light; reflects green light ➢ Carotenoids - absorbs green light; reflects orange, red, yellow light ➢ Phycobilins - found in red algae, absorb wide spectrum of light ❖ Light-dependent reactions & Light-independent reactions ➢ Light-dependent reactions ■ Requires light ■ Produces lots of ATP + provides protons for light-independent reactions ■ Occurs in grana of chloroplasts (in thylakoids) ● Thylakoids have many photosystems, which have chlorophyll a (as well as chlorophyll b and carotenoids) to absorb light ■ Energized electrons in chlorophyll molecules escape and move into ETCs. ● Energy is used to form proton gradient + power ATP production by ATP synthase (chemiosmosis; same as cell respiration) ■ Water is broken down into parts: ● Electrons - replaces electrons that escaped from chlorophyll molecules ● Protons - establishes proton gradient + used by ATP synthase to produce ATP; NADP takes them to stroma for use in lightindependent reactions ● Oxygen - released as waste product ➢ Light-independent reactions ■ Does not require light ■ Produces sugar (PGAL: 3-carbon sugar); uses lots of ATP ■ Occurs in stroma of chloroplasts ■ Consists of the Calvin cycle, which incorporates CO2 into sugar (carbon fixation) ● Important enzyme for Calvin cycle: rubisco ❖ Leaf structure ➢ *photosynthesis mostly happens in palisade layer (tightly packed cells with chloroplasts) ➢ Spongy mesophyll cells have chloroplasts + photosynthesis occurs ■ Less tightly packed and have air spaces (lets oxygen, CO2, water vapor move throughout) ➢ Epidermis layer - clear + no photosynthesis; protects cells underneath ■ Layer of cutin: above epidermis, prevents loss of water ➢ Guard cells - makes stomata open/close, minimizing water loss