Cell Structure & Function

1. Cell Structure & Function Unit III Chapter 7

2. The History of the Microscope • In the 1600’s, Dutch businessman Anton van Leeuwenhoek became on of the first people to us a microscope to study nature • In 1665, English physicist Robert Hooke used one of the first light microscopes to look at thin slices of plant tissue • Under the microscope, the cork he was looking at seemed to be made of thousands of tiny chambers that he dubbed “cells” • Before long, it became apparent that cells were the basic unit of life

3. The Cell Theory • The collective discoveries of many biologists are summarized in the cell theory • The cell theory states the following: • All living things are composed of cells • Cells are the basic units of structure and function in living things • New cells are produced from existing cells

4. Types of Cells • Biologists divide cells into 2 categories: eukaryotes and prokaryotes • Prokaryotes: • Generally smaller and simpler than eukaryotes • Do not contain nuclei (no nucleus) • Example: all bacteria are prokaryotes • Eukaryotes: • cells have nucleus • contain dozens of specialized structures (called organelles) • Example: all plants, animals, and fungi are eukaryotes Prokaryote cell Eukaryote cell

5. Cell Structures: Cell Membrane • The cell membrane is a thin, flexible barrier around the cell that is selectively permeable • The main function of the cell membrane is to regulate what enters and leaves the cell and also to provide protection and support • The core of the cell membrane is a double-layered sheet called a lipid bilayer • Most cell membranes also contain protein molecules that run through the lipid bilayer (form channels & pumps to help move material across the cell membrane) • Carbohydrate molecules form chains that are attached to the outer surfaces of these proteins (act like chemical identification cards – allowing cells to identify one another)

6. The Cell Membrane

7. Cell Structures: Cell Wall • Cell walls are found in many organisms, including: • Plants • Algae • Fungi • Nearly all prokaryotes • ***ANIMAL CELLS DO NOT HAVE CELL WALLS*** • The main function of the cell wall is to provide support and protection for the cell • Most cell walls allow water, oxygen, carbon dioxide, and other substances to pass through them • Plant cell walls are made of cellulose

8. Cell Structures: Nucleus • Found only in eukaryotic cells • The function of a cell nucleus is to: • Control most cell processes • Contain the hereditary information of DNA – contains nearly all of a cell’s DNA

9. Cell Structure: Chromatin & Chromosomes • The granular material visible within the nucleus is called chromatin • Consists of DNA bound to protein • Most of the time, chromatin is spread throughout the nucleus • When cells divide, chromatin condenses to form chromosomes • These threadlike structures contain the genetic information that is passed from once cell to the next

10. Cell Structure: Nucleolus & Nuclear Envelope • Most nuclei contain a small, dense region known as the nucleolus • This is the site where the assembly of ribosomes begins • The nucleus is surrounded by a double-membrane layer called the nuclear envelope • Contains thousands of pores which allow material to move into and out of the nucleus

11. Cell Structures: Cytoskeleton • The cytoskeleton of a cell is a network of protein filaments that helps the cell maintain its shape • Also involved in many forms of cell movement • The cytoskeleton is made up of microtubules and microfilaments • Microtubules: hollow tubes of protein that help maintain cell shape & help to separate chromosomes during cell division • Microfilaments: long, thin fibers that function in the movement and support of the cell & helps to move the organelles within the cell

12. Organelles in the Cytoplasm • The cytoplasm contains many important structures known as organelles: • Ribosomes • Endoplasmic reticulum • Golgi apparatus • Lysosomes • Vacuoles • Chloroplasts • Mitochondra

13. Ribosomes • Ribosomes are the site of protein synthesis within the cell • The site where proteins are assembled following coded instructions that come from the nucleus

14. Endoplasmic Reticulum • The endoplasmic reticulum is the organelle in which components of the cell membrane are assembled and some proteins are modified • Rough Endoplasmic Reticulum: the part of the ER that is involved in the synthesis of proteins – has ribosomes on its surface • Smooth Endoplasmic Reticulum: do not have ribosomes on its surface – contains enzymes that function in the synthesis of lipids Rough ER Smooth ER

15. Golgi Apparatus • Enzymes in the golgi apparatus attach carbohydrates and lipids to proteins • From the golgi, proteins are sent to their final destination

16. Lysosomes • Lysosomes are small organelles filled with enzymes • Lysosomes break down lipids, carbohydrates, and proteins for use by other parts of the cell • Lysosomes also remove debris that might otherwise clutter up the cell • known as the “garbage disposals” of the cell

17. Vacuoles • Vacuoles are found only in eukaryotic plant cells • Plant cells often store materials such as water, salts, proteins, and carbohydrates in saclike structures called vacuoles • Many plant cells have a single large, central vacuole filled with liquids • Pressure in these central vacuoles allow plants to support heavy structures such as leaves & flowers

18. Chloroplasts • Chloroplasts are found in plants and some other organisms • Chloroplasts use energy from the sunlight to make energy-rich food molecules by photosynthesis

19. Mitochondria • Mitochondria are the site of ATP (energy) production in the cell • Mitochondria use energy from food to make high-energy compounds that the cell can use for power

20. Cellular Transport Cells Notes Part 2

21. Passive Transport • Passive transport is the diffusion (movement) of a substance across a membrane where NO ENERGY is used • In a solution, molecules move constantly! The molecules tend to move from an area where they are more concentrated to an area where they are less concentrated (a process known as diffusion) • Diffusion causes many substances to move across a cell membrane from an area of higher concentration to an area of lower concentration but does NOT require the cell to use energy • Alcohol • Water • Small lipids

22. Osmosis • Osmosis is the diffusion of WATER through a selectively permeable membrane • Although water molecules move in both directions across the membrane, there is a net movement of water into the compartment containing the most solutes (i.e. least water) • Since osmosis is a form of passive diffusion, it requires NO energy • Water will move across a membrane until equilibrium is reached

23. Osmosis (more water) (more sugar)

24. Facilitated Diffusion • Some molecules are too large to cross the lipid bilayer of the cell membrane but do diffuse through protein channels found within the lipid bilayer of the cell membrane • This process is known as facilitated diffusion • Facilitated diffusion is the movement of specific molecules across a cell membrane through protein channels • This process occurs WITHOUT energy and the net movement of the molecules will be from an area of higher concentration to an area of lower concentration

25. Active Transport • Often, material needs to move across a cell membrane against a concentration gradient • Active transport is the movement of materials across a membrane from an area of lower concentration to an area of higher concentration • Active transport REQUIRES energy • endocytosis • phagocytosis • exocytosis

26. Endocytosis • Endocytosis is the process by which a cell takes material into the cell by infolding of the cell membrane • Endocytosis is a form of ACTIVE TRANSPORT and requires energy

27. Phagocytosis • When large particles are taken into the cell by endocytosis, the process in known as phagocytosis • Phagocytosis is the process in which extensions of cytoplasm surround and engulf large particles and take them into the cell • Phagocytosis is a form of ACTIVE TRANSPORT and therefore REQUIRES energy • Pinocytosis is a form of endocytosis where small particles are take in by the cell

28. Exocytosis • Exocytosis is a process by which a cell releases large amounts of material • During exocytosis, the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell • Exocytosis is a form of ACTIVE TRANSPORT and REQUIRES energy

29. Types of Solutions • All of the components of a solution are evenly distributed throughout the solution • The substance that is dissolved is the solute • The substance in which the solute is dissolved is the solvent • Example: salt/water mixture – salt is the solute and water is the solvent • A solution may be • Hypertonic • Hypotonic • Isotonic

30. Types of Solutions • A hypertonic solution is one in which there are more solutes (particles) than solvent (liquid) • A hypotonic solution is one in which there is less solute (particles) than solvent (liquid) • An isotonic solution is one in which there is an equal solute/solvent ratio • NOTE: the terms hyper, hypo, iso are referring to the outside environment in which something is placed

31. Movement of Molecules in Solution • A cell placed in an isotonic solution will remain the same as when it was put into the solution • This is known as equilibrium • If a cell is placed in a hypertonic solution (i.e. more salt in the solution than is inside the cell), the net movement of water will be OUT of the cell and the cell will SHRINK • Because osmosis moves water from an area where there is more water to an area where there is less water • If a cell is placed in a hypotonic solution (i.e. less salt in the solution than is inside the cell), the net movement of water will be INTO the cell and the cell will swell and burst • Because osmosis moves water from an area where there is more water to an area where there is less water

32. Movement Through the Membrane • The cell membrane regulates what enters and leaves the cells and also provides protection and support (a.k.a. selectively permeable to certain substances) • The core of nearly all cell membranes is a double-layered sheet called a lipid bilayer • The 2 types of movement that can occur across a cell membrane are: • Passive transport – does not require energy • Osmosis, diffusion, facilitated diffusion • Active transport – requires energy • Endocytosis, exocytosis, phagocytosis