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Unit 3, Part 2 Notes – Cell Structure and Function Ms. Ottolini, AP Biology

1. What are the parts of the cell theory? -All living things are made of cells -Cells are the basic unit of structure and function -Cells are derived from existing cells (in other words, new cells are created from the division of old cells)

2. What traits are found all cells? -They are surrounded by plasma (cell) membrane. -They contain a semifluid substance called the cytosol and organelles (structures within the cell with specific functions) -Together the cytosol and the organelles make up the space between the membrane and the nucleus (called the cytoplasm) -They contain chromosomes (organized DNA) -They have ribosomes (used to make proteins)

3. What size is a typical cell? -Most bacteria and archaea (i.e. prokaryotic cells) - 1-10 µm (=micrometers) – SEE IMAGE TO THE RIGHT -Eukaryotic cells -10-100 µm – SEE IMAGES OF PLANT AND ANIMAL CELLS BELOW

-Cells cannot get too large because as they increase in size, their volume increases faster than their membrane surface area (SA/volume ratio decreases) -Because the ratio of the membrane surface area to the volume decreases at large cell sizes, large cells can’t transport food/oxygen/waste fast enough -To solve this problem, large organisms have MORE cells; NOT BIGGER cells -Certain cell shapes (ex: intestinal cells containing membrane folds called microvilli) can increase the surface area of the membrane and therefore increase transport across the membrane –SEE IMAGE TO THE RIGHT

4. How are eukaryotic cells organized? -Eukaryotic cells have systems of internal membranes (made mostly of phospholipids and integral membrane proteins) to divide the cell into different compartments with different chemical conditions and different functions 5. How is the nucleus (found in eukaryotic cells ONLY) organized? -The nucleus is surrounded by a double membrane with holes (i.e. nuclear pores) lined by special proteins to regulate the passage of molecules in and out of the nucleus -DNA exists within the nucleus as chromatin (DNA loosely coiled around proteins) or chromosomes (super-coiled/ tightly packed DNA… formation of chromosomes only occurs prior to cell division) -At the middle of the nucleus is a dense sphere called the nucleolus that creates ribosomes

6. What is the structure, function, and location of ribosomes? -Ribosomes are made of proteins and RNA. They are one of the only organelles found in both eukaryotic and prokaryotic cells. They are not surrounded by a membrane. -Ribosomes are used to synthesize proteins -Ribosomes can be found suspended in the cytosol. These are called free ribosomes and they are used to create proteins that will be used in the cytosol. Ribosomes are also found attached to the Rough ER or nuclear envelope. These are called bound ribosomes and the are used to create proteins that are sent through the endomembrane system to a final destination of the cell membrane (ex: to become channel proteins or protein pumps). These proteins may also be exported from the cell to act as signaling molecules between cells (ex: hormones).

7. What is the endomembrane system and how is it used to send proteins out of the cell? -The endomembrane system is a network of organelles made of membrane. These organelles are all involved in synthesis, modification, or packaging of proteins to be sent from the cell. -Ribosomes on the nuclear envelope or rough ER create proteins. These proteins enter the ER inner space (called the lumen) and may be modified by enzymes in this inner space. For example, certain proteins receive carbohydrate chains to become glycoproteins used on the surface of the cell membrane for cell-cell recognition. -The proteins created and modified travel to the Golgi apparatus via vesicles (small membrane sacs) that bud off of the ER and later fuse with the cis side of the Golgi. (Note: the Cis side of the Golgi is closer to the ER and farther from the cell membrane) -In the tubes/sacs of the Golgi (the cisternae), proteins are modified by more enzymes that can break off parts of proteins or add additional molecules on. These proteins are then packaged into new vesicles that bud off the trans side of the Golgi and later fuse with the cell membrane to release their contents outside of the cell. (Note: the Trans side of the Golgi is closer to the cell membrane and farther from the ER.) 8. What is the structure, function, and location of the endoplasmic reticulum? -The ER is a system of tubes of membranes. The space inside these tubes is called the ER lumen. -The ER is attached to the nuclear membrane. -There are two parts to the ER – the Rough ER and the Smooth ER

-The Rough ER has ribosomes attached and is particularly abundant in cells that secrete high amounts of proteins (because ribosomes make proteins!) -Proteins created on the attached ribosomes are inserted into the ER lumen and folded into their 3D shape. -Modifications (ex: addition of carbohydrate chains) may occur in the ER lumen before a protein is folded. -Membrane or secretory proteins are packaged into vesicles and sent to the Golgi. (Note: secretory proteins are proteins that will ultimately be secreted from / leave the cell) -The Rough ER is also used to create more membrane phospholipids that can be sent to other parts of the cell

-The Smooth ER does not have attached ribosomes. -It contains enzymes for many different processes (ex: synthesizing oils, steroids, phospholipids – all types of lipids!) -Liver cells have a high amount of smooth ER because the smooth ER can also be used to break down toxins (ex: nitrogen waste from cells, drugs, alcohol) -Muscle cells also have a high amount of smooth ER because the smooth ER can help store Ca++ ions to regulate muscle contraction -Note: Frequent drug use leads to increased smooth ER for increased break down… increased amount of smooth ER is the reason why tolerance increases and higher dose is needed for same effect AND why frequent/extreme drug use leads to liver damage (i.e. cirrhosis)

9. What is the structure, function, and location of the Golgi apparatus? -The Golgi looks like a stack of pancakes or flattened membrane sacs called cisternae -Is considered the post office of the cell. It is where secretory proteins and other molecules destined to leave the cell are modified and packaged. -There is a large Golgi in the cells of the pancreas because they produce large amounts of hormones like glucagon and insulin that must be exported (sent) from the cell) -Products are modified as they pass from the cis to trans side. They are also sorted and packaged into vesicles. -The Golgi adds molecular ID tags to products to aid in sorting. Identifiers such as phosphate groups act like ZIP codes to identify product’s final destination 10. What is the structure, function, and location of lysosomes? -Lysosomes are found only in animal cells (not plant cells) -The are membrane-bound sacs containing hydrolytic (digestive) enzymes -The enzymes made by ribosomes on rough ER/modified in Golgi -The enzymes can hydrolyze food, whole cells, damaged cell parts -Lysosomes are an example of compartmentalization (maintaining separate environments in different parts of the cell in order to perform specific functions) - enzymes work best at pH 5 - H+ ions pumped from cytosol into lysosome - if a lysosome ruptures, enzymes not very active in cytosol (neutral pH) (prevents accidental “self digestion”) - Massive rupture of many lysosomes can destroy a cell by “self digestion” (autophagy) -Lysosomes are used for the following functions: -Digestion of food in unicellular organisms -Recycling of cell’s organelles and macromolecules -Programmed cell death (apoptosis) - apoptosis is important in embryonic development (form fingers/lose tail) - apoptosis occurs in cells that are damaged and get the signal to self destruct (Cancer cells and HIV infected cells don’t respond to signal) -Tay-Sachs is a genetic disorder in which people lack lysosomal enzymes needed to break down lipids, which results in accumulation of lipids in the brain (causing blindness, seizures, and eventually death)

11. What is the structure, function, and location of vacuoles? -Vacuoles are larger versions of vesicles (membrane-bound sacs with varied functions) -Food vacuoles form by phagocytosis of food particles. They join / fuse with lysosomes so that the food particles can be digested. -Contractile vacuoles are found in freshwater protists (single celled eukaryotic organisms). They pump excess water out that enters from the outside freshwater via osmosis. -There is a large central vacuole in many mature plant cells used to store proteins, ions (ex: K+, Na+, Cl-), pigments, defensive molecules (to defend the plant against herbivores), water, etc. -The large vacuole reduces the area of the cytosol, so the surface area / volume ratio of the cell increases

12. What is the structure, function, and location of mitochondria? -A double membrane surrounds the mitochondrion. The inner membrane is folded to maximize surface area for the reactions of cellular respiration. The different compartments between and inside membranes of the mitochondrion are used for different parts of the reactions of cellular respiration. -Cellular respiration involves breaking down sugars, fats, and other molecules in the presence of oxygen to generate ATP -Cells with high energy needs (EX: muscle cells) have large numbers of mitochondria

13. What is the structure, function, and location of chloroplasts? -A double membrane surrounds the chloroplast. There are also stacks of membrane sacs located inside the inner membrane. The different compartments between and inside membranes of the chloroplasts are used for different parts of the reactions of photosynthesis. -Photosynthesis involves the conversion of solar energy to chemical energy by using the energy

from sunlight to rearrange the atoms in CO2 and

H2O to create glucose (C6H12O6). 14. What is the endosymbiotic theory? -The endosymbiotic theory says that prokaryotes were engulfed by larger cells, shared a symbiotic relationship with the host cell, and eventually became organelles within the larger cells (ex: mitochondria and chloroplasts) shared symbiotic relationship with host cell -Example of symbiosis: A mitochondrion provided energy for the larger cell and the cell provided protection for the larger cell -The endosymbiotic theory says that the first eukaryotic cells (cells with membrane-bound organelles like mitochondria and chloroplasts) arose by a small cell being swallowed by a larger cell. -Evidence for endosymbiosis: -Mitochondria and chloroplasts are the only organelles besides nucleus with their own DNA and double membranes -Mitochondria and chloroplasts have their own ribosomes -The inner membranes of mitochondria and chloroplasts have enzymes and transport systems similar to bacterial plasma membranes -Mitochondria can replicate independently of the nucleus using binary fission, a process of cell division found in free- living bacteria

15. What is the structure, function, and location of the cytoskeleton?

-The similarities between the cytoskeleton in all eukaryotic cells provides evidence for the relatedness of all eukaryotic organisms. -The cytoskeleton is made of a network of protein fibers extending throughout the cytoplasm. The three different types of protein fibers are microtubules, intermediate filaments, and microfilaments -The cytoskeleton provides mechanical support for organelles and maintains cell shape -It can be changed by disassembling the cytoskeleton in one part and reassembling it in another (changes shape of cell) -Organelles can travel around the cell by moving around on cytoskeletal protein “tracks” (like train tracks)

16. What is the structure, function, and location of cilia and flagella? -These “hairs” or “tails” extend from cell surface and are used for movement -They are made of microtubules (like the microtubules found in the cytoskeleton) that are arranged in a 9+2 pattern (nine doublets in a ring around a pair in the center) -Motor proteins called “dynein arms” walk along

microtubules and cause bending and movement, which requires ATP -Cilia are short and numerous, whereas flagella are long and there are only one to a few on each cell

17. What is the structure, function, and location of the plant cell wall? -Note: prokaryotes, fungi, and some protists also have cell walls -The cell wall is used for the following functions: protection, support, and maintaining cell shape -The cell wall of plants is mostly made of the polysaccharide cellulose, whereas the cell wall of bacteria is made of the polysaccharide peptidoglycan, and the cell wall of fungi is made of the polysaccharide chitin -Plasmodesmata are holes / pores in the cell walls of two adjacent (neighboring) plant cells that connect their cytosols and allow water / small solutes / proteins to pass freely from one plant cell to another to make the whole plant a continuous unit

18. What is the structure, function, and location of the animal extracellular matrix (ECM)? -The extracellular matrix is located outside the cell membrane of animal cells -It is composed of glycoproteins (proteins with attached carbohydrate chains) secreted by the cell -The most common ECM glycoprotein is collagen -The ECM strengthens cells, and connects cells together so they can act as a unit (a group of cells with similar functions = a tissue) 19. What types of structures in the ECM connect cells together? -Tight junctions and desmosomes (aka adhesion junctions) fasten cells together -Gap junctions act like plasmodesmata in plant cells and provide channels between adjacent cells to allow molecules to pass between cells