BIO Ch 2B PDF

Announcements Exam 1 is everything learned so far in the class Quiz questions may also be on exam Chapter 2b: Enzymes Enzymes Structure defines function Enzymes are proteins that initiate and speed up chemical reactions Protein shape is particularly critical in enzymes, molecules...

Announcements Exam 1 is everything learned so far in the class Quiz questions may also be on exam Chapter 2b: Enzymes Enzymes Structure defines function Enzymes are proteins that initiate and speed up chemical reactions Protein shape is particularly critical in enzymes, molecules that help initiate and accelerate the chemical reactions in our bodies Enzymes emerge in their original form when the reaction is complete and this can be used again and again Enzymes facilitate chemical reasons Enzymes can help to bring about chemical reactions in a variety of ways. The enzyme lactase, for example, breaks down the milk sugar lactose into two simple sugars that can be used for energy Activation Energy Chemical reactions occurring in organisms can either release energy or consume energy In either case, the reaction needs a little “push” in order to initiate the reactions= called activation energy Enzymes act as catalyst by lowering activation energy An enzyme can reduce the activation energy in 4 ways ○ By stressing, bending, or stretching critical chemical bonds ○ By directly participating in the reaction ○ By creating a microhabitat that is conducive to the reaction ○ By simply orienting or holding substrate molecules in place so that they can be modified All reactions take place in some aqueous solution Lactase catalyzes breakdown of lactose into glucose and galactose by: ○ Stressing and bending the covalent bond between the two sugars ○ Directly participating in the reaction ○ Creating a microhabitat conducive for bond breaking ○ Reorienting the molecule in space Enzymes regulate reactions in several ways (but malformed enzymes can cause problems) The rate at which an enzyme catalyzes a reaction is influenced by several chemical and physical factors ○ Reaction rates increase with increased amounts of enzyme, but only up to the point at which all of the enzyme molecules are bound to substrate. At that point, additional enzyme (or substrate) no longer increase the reaction rate.  ○ Reaction rates generally increase at higher temperatures, but only up to the optimum temperature for an enzyme. At temperatures above the optimum, reaction rates decrease as enzymes denature. ○ Reaction rates generally increase as pH nears the optimum level for an enzyme. Above or below this pH, enzyme function can be disrupted and reaction rates Competitive inhibitors bind to the active site, blocking substrate molecules from the site and thus from taking part in the reaction. ○ Noncompetitive inhibitors do not compete for the active site bur bind to another party of the enzyme, altering its shape in a way that changes the structure of the active site, reducing or blocking its ability Non-functioning enzymes ○ Sometimes a protein “word” Cells Prokaryotic cells are structurally simple but extremely diverse Every cell on earth falls into one of two basic categories: ○ A eukaryotic cell has a central control structure called a nucleus which contains the cell’s DNA (eukaryotes) Contains organelles ○ A prokaryotic cell does not have a nucleus or organelles; its DNA simply resides in the middle of the cell (prokaryotes) No organelles The prokaryote: Basic structure ○ 4 structures in all prokaryotes (intracellular) Plasma membrane: encloses cell contents: DNA, ribosomes, and cytoplasm Cytoplasm: jelly-like fluid inside cell DNA: one or more circular loops containing genetic information Ribosomes: granular bodies in the cytoplasm that convert genetic information into protein structure ○ Additional structures (extracellular) Important to note: May be different depending on species of prokaryote Cell wall: protects and gives shape to the cell Capsule: protective outer coating Pili: hair-like projections that help cells attach to other surfaces and sometimes play a role in DNA transfer Flagellum: whip-like projection(s) that aids in cellular movement  Eukaryotic vs prokaryotic cells ○ Typical eukaryotic cell features include DNA contained in nucleus, larger than prokaryotes (usually at least 10x bigger), cytoplasm contains specialized structures called organelles ○ Typical prokaryotic cell features include no nucleus (DNA is in the cytoplasm), internal structure mostly not organized into compartments, much smaller than eukaryotes Eukaryotic cells have compartments with specialized functions Theory: organelles may have developed by endosymbiosis or invagination or a combination of the two ○ Endosymbiosis theory: developed to explain the presence of two organelles in eukaryotes, chloroplasts in plants and algae, and the mitochondria in plants and animals Endosymbiosis: ancestor to eukaryotes Ancestral eukaryote engulfs prokaryotes then merge and overtime, the engulfed prokaryote evolves into an organelle such as mitochondria or a chloroplast ○ Invagination: ancestor to eukaryotes Plasma membrane folds in on itself then inner compartments (organelles) are formed Every cell is bordered by a plasma membrane ○ Like gatekeepers, cell membranes control the movement of material into and out of the cell ○ Plasma membrane are made up of two layers that are filled with a variety of pores, molecules, and channels ○ Functions include holds contents of cell in place, take in food and nutrients, aids in building and exporting molecules, allows interactions with the environment and neighboring cells ○ Plasma membrane is made up of phospholipid bilayer Structure: Hydrophilic head (polar) is attracted to water and composed of glycerol linked to a phosphorus-containing molecule  Hydrophobic tails (nonpolar) is not attracted to water and is composed of carbon-hydrogen chains Hydrophilic heads extends toward the intracellular and extracellular fluid, and hydrophobic tails are directed away from the watery fluids Molecules embedded within the plasma membrane help it performs its functions ○ Plasma membrane is a fluid mosaic In addition to proteins, two other molecules are found in the plasma membrane: short, branched carbohydrate chains and cholesterol There are 4 primary types of membrane proteins, each of which performs a different function ○ Receptor proteins bind to external chemicals in order to regulate processes within the cell ○ Recognition proteins provide a “fingerprint” for the cell, so it can be recognized by the other cells ○ Transport proteins provide a passageway for molecules to travel into and out of a cell ○ Membrane enzymes accelerate intracellular and extracellular reactions on the plasma membrane 9 important landmarks distinguish eukaryotic cells ○ The nucleus is the cell’s genetic control center The nucleus has two primary functions: genetic control center. Storehouse for hereditary information ○ Nuclear membrane consists of two bilayers on top of each ○ Nucleus function: Acts as the genetic control center of the cell Stores hereditary information Chromatin is a mass of long, thin fibers consisting of DNA with some proteins attached ○ During cell division, the chromatin coils up and the threads become shorter and thicker until they become visible as chromosomes Nucleolus is an area near the center of the nucleus where subunits of the ribosomes are assembled Cytoplasm and cytoskeleton form the cell’s internal environment ○ Cytoskeleton has 3 chief purposes: Give animal cell shape and support Controls the intracellular traffic flow Is dynamic and can generate force ○ Cytoskeleton consists of 3 types of protein fibers: Microtubules (2) Intermediate filaments (1) Microfilaments (3) ○ 3 types of protein fibers in the cytoskeleton Microtubules: thick, hollow tubes  The tracks to which molecules and organelles may attache and be moved along Intermediate filaments are durab;e. Rope-like systems of numerous overlap proteins ○ Give cells great strength Microfilaments are long, solid rod-like fibers who can help with cell contraction and cell division ○ Cilia and Flagellum (eukaryote) Are short projections that often occur in large numbers ona single cell and beat swiftly, often in unison Flagella are longer than cilia, found in some prokaryotes and single celled eukaryotes Make whip-like rapid movement in sperm possible Mitochondria are the cell’s energy converters (to convert food energy in to ATP, CO2 and H20 ○ Functions include acting as all=purpose energy converters and harvesting energy to be used for cellular functions ○ Human mitochondria consume as much as 80% of the oxygen we breathe ○ Heart has the most mitochondria ○ Mitochondria has an intermembrane space and the matrix Many folds increase surface area Lysosomes are round, membrane-enclosed, acid-filled vesicles that function as garbage disposals ○ Function: act as floating garbage disposals for cells, digesting and recycling cellular waste products and consumed material Hydrolytic enzymes Peroxisomes are specialized for carrying out oxidative reactions using molecular oxygen ○ They generate hydrogen peroxide (H2O2), which they use for oxidative purposes destroying the excess by any means of the catalase they contain ○ Like free radical scavengers In the endoplasmic reticulum, cells build proteins and disarm toxins ○ Over of the endomembrane system functions Produces and modifies molecules to be exported to other parts of the organism Breaks down toxic chemicals and cellular by-products Includes: rough ER, smooth ER, and golgi apparatus ○ Rough ER modifies proteins that will be shipped to other locations in the endomembrane system ○ Smooth ER synthesizes lipids such as fatty acids, phospholipids, and steroids Also detoxifies molecules such as alcohol, drugs, and metabolic waste products Ex: human liver cells ○ Golgi apparatus is where the cell processes products for delivery throughout the body  Processes and packages proteins, lipids, and other molecules for export to other locations inside and outside the cell Plant cells The cell wall provides additional protection and support for plant cells ○ Functions include structural strength, increased water resistance, and protection from insects and other animals ○ Plasmodesmata are channels connecting adjacent cells, allowing the passage of some molecules between them The cell wall is an organelle found in plants ○ It is primarily from carbohydrate cellulose and it surrounds the plasma membrane of a plant cell The cell wall confers tremendous structural strength and gives plants increased water resistance, and provides some protection from insects and other animals that might eat them In plants, plasmodesmata connect cells and enable communication and transport between them. Vacuoles are multipurpose storage sacs for cells ○ Functions include nutrient storage, waste management, predator deterrence, sexual reproduction, and physical support Chloroplasts are the plant cell’s power plant ○ The stroma and interconnected little flattened sacs called thylakoids Endosymbiosis theory revisited ○ Chloroplasts resemble photosynthetic bacteria ○ Circular DNA ○ Dual outer membrane Practice Questions 1. Which component of a prokaryotic cell would NOT be considered intracellular? a. Cytoplasm b. Ribosomes c. DNA d. Flagellum 2. Which can be found in BOTH eukaryotic and prokaryotic cells? a. Nucleus b. Mitochondria c. Ribosomes d. Membrane bound organelles e. Pili 3. Why are plasma membranes such complex structures? a. They perform five critical functions: (1) Take in food and nutrients, (2) Dispose of waste products, (3) Build and export molecules, (4) Regulate heat exchange and (5) Regulate flow of materials in and out of cell. 4. Why are the fatty acid tails of a phospholipid hydrophobic? a. They are composed of carbon-hydrogen bonds b. They are composed of carbon-oxygen bonds c. They are composed of glycerol and phosphorus d. They are polar 5. Which answer below is NOT a feature of the nucleus? a. It is an organelle surrounded by a lipid bilayer b. It contains a ribosome assembly area (nucleolus) c. It contains chromatin d. Small molecules, RNA, and proteins can enter or leave through nuclear pores 6. The main component of cilia and flagella is: a. Microtubules b. Microfilaments c. Intermediate filaments d. Both 1 and 2 7. What evidence supports endosymbiosis as the origin for mitochondria? a. Presence of two lipid bilayers b. Mitochondria have their own DNA c. Maternal inheritance d. Both 1 and 2 e. All of the above 8. Which function is specific to a chloroplast? a. Used for detoxification b. Garbage disposal of the cells c. Used to maintain turgor pressure d. Converts light into chemical energy e. Converts chemical energy into ATP