Unit 2 – Cell Structure and Function

1. Unit 2 – Cell Structure and Function • Cell Theory – The concept was formally articulated in 1839 by Schleiden & Schwann and has remained as the foundation of modern biology. • 6 main components of cell theory:  • All known living things are made up of cells. • The cell is structural & functional unit of all living things. • All cells come from pre-existing cells by division. (Spontaneous Generation does not occur). • Cells contains hereditary information which is passed from cell to cell during cell division. • All cells are basically the same in chemical composition. • All energy flow (metabolism & biochemistry) of life occurs within cells.

2. Types of cells • Two main types of cells exist: prokaryotes and eukaryotes • Prokaryotes (pro – “before”, kary – “nucleus”) • lack a membrane bound nucleus • No organelles (mitochondrion, chloroplast, etc. • Bacteria and cyanobacteria (monerans) • Primitive structure • Reproduce by simple fission (division) • Smaller than eukaryotes

3. Types of Cells - continued • Eukaryotes (eu – “true”, kary – “nucleus”) • Plants, animals, protists, and fungi • Possess a nucleus and membrane bound organelles • Larger and more advanced than prokaryotic cells • more complex cellular division

4. Questions 1-3, p 72 • How did improvements in the microscope help scientists form the cell theory? • Improvements allowed scientists to see cells in greater and greater detail and enabled them to discover cells in all types of living matter. • How do prokaryotic and eukaryotic cells differ? • Eukaryotic cells have a nucleus and membrane-bound organelles, prokaryotic cells do not. • Analyze – Today, scientists can study human cells grown in petri dishes. Explain how this technique builds on the work of early scientists. • Once it was understood that cells were the basic building block of living matter, scientists could concentrate on describing different types of cells and discovering the relationships between cell type and cell function. One way to do this is too isolate the cell itself.

5. Questions 4 &5, p72 • Compare – In what ways are cells similar to atoms? • Both are basic units, or building blocks. The atom is the basic unit of matter; the cell is the basic unit of living organisms. • Medicine – Suppose a certain poison kills human cells by blocking pores in the nuclear membrane. Explain why it would or would not kill bacteria. • It would not kill bacteria because bacteria do not have a nucleus, so there are no nuclear pores to be blocked.

6. Cell Components • 1. Cytoplasm • The cytoplasm is the region outside the nucleus and is the location where nutrients are absorbed, transported, and processed including the cytosol (fluid soup of the cell) and the organelles. • The cytoplasm stores the waste until proper disposal can be carried out. • Both the nucleus and the cytoplasm are collectively referred to as the protoplasm. • The cytoplasmic organelles are the parts of the cell found in the cytoplasm.

7. 2. Plasma Membrane (Cell membrane) • The cell membrane is the outer most edge of the cell. It is also referred to as the plasma membrane. • It holds the contents of the cell in place and regulates the movement of molecules in and out of the cell. • The plasma membrane is composed of a double layer of lipid molecules with protein molecules embedded in it. • A lipid molecule consists of two parts, a polar head and a non-polar chain tail. The polar end is hydrophilic, an attraction with water, while the non-polar tail is hydrophobic, repels water. • Like molecules (polar / non-polar) attract while unlike molecules repel.

8. 3. Nucleus • The nucleus is the cell’s control centre. • It is round and surrounded by a double membrane called the nuclear envelope. • The nucleus contains most of the genes (genetic material). • The dark region found in the nucleus is called the nucleolus. • The nucleolus is responsible for the formation of ribosomes.

9. 4. Mitochondria(pl) mitochondrion (s) • Tiny oval shaped organelles called mitochondria are often referred to as the “power plant” of the cell. • They provide the body with needed energy through a process called respiration. The equation for respiration is: ??? • Mitochondria are found in both plant and animal cells. • In respiration, chemical bond energy is converted into other forms of energy. Mitochondria are found where energy is most often needed (muscles). • Special enzymes that assist the breaking down of sugar molecules are found within the mitochondria. • When a sugar molecule is broken up, 36% of the energy is converted to ATP, while the remaining 64% is heat. • Mitochondria have two separate membranes: a smooth outer membrane and a folding inner membrane. • The inner membrane consists of finger-like projections called cristae.

10. 5. Ribosomes • Ribosomes are the organelles responsible for the synthesis of proteins. • They are one of the smallest organelles found in the cytoplasm. • A ribosome is made up of two parts. The mRNA molecule attaches between the two parts and is fed through the ribosome in protein synthesis. • The ribosomes are located on the endoplasmic reticulum (ER).

11. 6. Endoplasmic Reticulum (ER) • The ER is a series of canals that carry material throughout the cytoplasm. • The canals, composed of flattened parallel membranes are referred to as ER. • There are two types of ER: • 1. Smooth ER: No ribosomes; appear flat • 2. Rough ER: Has ribosomes attached to it; appears bumpy • Rough ER is found mostly where enzymes are needed since the ribosomes make enzymes (which are a type of protein). • Smooth ER is found where lipids are synthesized.

12. 7. Golgi Apparatus • The Golgi apparatus appears like a stack of pancakes, but is actually a bunch of membranous sacs piled on one another. • In the Golgi apparatus, protein molecules are stored after being produced by the ribosomes. • The Golgi apparatus will move to the plasma membrane and then fuse or stick to it. At this point, small packages called vesicles are released out of the cell. For more information refer to transport of molecules.

13. 8. Lysosomes • Lysosomes are vesicles containing a variety of digestive enzymes that help break down large molecules and worn-out cell parts. • They are formed by the Golgi apparatus. • They play an important role in the defence mechanism of the human body by destroying harmful substances that find their way into the cell. • They also release digestive enzymes that break down bacteria.

14. 9. Centrioles • Centrioles are paired cylindrical structures that play an important role in cell division. • They are responsible for separating the chromosomes into two different cells. • Are only found in animal cells. • The centrioles are produced by the centrosomes (make microtubules – centrosomes are found in both plant and animal cells).

15. 10. Vacuole • A large part of the cytoplasm in plant cells is composed of a fluid-filled space called a vacuole. • The vacuole serves as a storage space for sugars, minerals, and proteins. • It may be referred to as a contractile vacuole when it increases and decreases in size. • It will change it’s size for two reasons: 1. To change the pressure of the cell 2. To regulate the rate of absorption of minerals

16. 11. Chloroplast • Chloroplasts are the location for photosynthesis. • They contain a green pigment called chlorophyll. • They are not found in animal cells.

17. 12. Cell Wall • Most plant cells are surrounded by a non-living cell wall. • Cell walls are composed of cellulose. • Their main function is to protect and support the plant. • Some plants will have a secondary cell wall that is used for additional support.

18. Cool Cells website: • http://www.wiley.com/legacy/college/boyer/0470003790/animations/cell_structure/cell_structure.htm

19. Questions 1-3, p 79 • What are the functions of the cytoskeleton? • The cytoskeleton supports and shapes a cell, helps position and transport organelles, provides strength, assists in cell division, and aids cell movement. • Describe the structure of the nucleus. • The nucleus is surrounded by a double membrane with pores that connect its interior to the cytoplasm. DNA and the nucleolus are located inside the nucleus. • Explain the structure and function of the mitochondrion. • A mitochondrion supplies energy to a cell by releasing the energy stored in food molecules. The outer membrane surrounds a highly folded inner membrane where chemical activity occurs. It has its own ribosomes and DNA.

20. Questions 4-6, p 79 • What function does the cell wall perform in a plant? • The cell wall protects, supports, and shapes a plant cell, and regulates what moves into the cell. The cell walls of multiple cells can help support the entire plant. • Compare – What similarities do mitochondria and chloroplasts share? • Both membranes-bound organelles have their own DNA and help make energy available to the cell. • Compare – Describe how the endoplasmic reticulum, mitochondrion, and Golgi apparatus are structurally similar. • All are composed of membrane-enclosed chambers. The surface area of each is greatly increased by folds and layers.

21. Question 7, p 79 • Health – Medicine, alcohol, and many drugs are detoxified in liver cells. Why do you think the liver cells of some people who abuse alcohol and drugs have an increased amount of smooth ER? • Increased amounts of smooth ER in the livers cells suggests that the cells have responded to increased amounts of toxins by producing more smooth ER to handle the processing.