2 The History of Cell Studies 1. Robert Hook (1665) used a microscope to examine a thin slice of cork. The little boxes he observed reminded him of the small rooms (CELLS) in which the monks lived. He coined the use of the word cell. 2. Leeuwenhoek (1673) was the first to see and describe living cells (microorganisms) in drops of pond water using his single lens microscope. 3. Schleiden (1838) was a German Botanist who concluded that all plants were made of cells. 4. Schwann (1839) was a German Zoologist who stated that all animals were made of cells. 5. Virchow (1855) concluded that new cells could be produced only from the division of preexisting cells. 6. The cell theory states: a. All living things are composed of cells. b. Cells are the basic units of structure and function in living things. c. new cells are produced from existing cells.
3 Cell Structure Two categories of cells: Prokaryotic & Eukaryotic 2. Cells are placed into these categories based on whether they have a true membrane bound nucleus as well as other membrane bound organelles. 3. Prokaryotic cells are generally smaller and more primitive than eukaryotic cells. They do not have a true nucleus. They have no membrane bound organelles. Many of their chemical reactions take place along the cell membrane. 4. Eukaryotic cells are generally larger and more complex than prokaryotic cells. A eukaryotic cell has a nucleus surrounded by a nuclear membrane as well as many membrane bound organelles (mitochondria, chloroplasts, Golgi, ER, vacuoles) 5. The bacteria and archaebacterial are prokaryotic. 6. All cells other than bacteria and archaebacterial are eukaryotic. 7. All cells are surrounded by a barrier called a cell membrane. All cell contain genetic material in the form of DNA.
4 The Plant Cell 1. Chloroplast 2. Nucleus 3. Nucleoli 4. Cytoplasm 5. Cell Wall 6. Cell Membrane 7. Central Vacuole 8. Cell Wall, chloroplasts & central vacuole 9. The Central Vacuole is filled with water creating turgor pressure. This aids the cell wall in giving strength and support to the cell.
6 Mitochondria & Chloroplasts 1. Both organelle are involved in the energy transformations of the cell. Mitochondria convert the energy stored in foods to ATP. Chloroplasts capture the energy from the sun and convert it to the chemical energy stored in molecules of glucose. 3. The inner membrane of the mitochondria has many long folds and loops. These folds and loops are called cristae. The cristae greatly increase the surface area of the inner membrane. Since the chemical reactions of respiration occur along the cristae membrane, this greatly increases the space for these chemical reactions to occur. 5. Every chloroplast contains stacks and stacks of thylakoids. Thylakoids contains chlorophyll. They increase the surface area for the absorption of energy from the sun
7 Ribosomes and ER 1. Ribosomes are not surrounded by a membrane. Ribosomes consist of 2 subunits a large & a small subunit. The subunits are composed of proteins & RNA & are manufactured by the nucleolus. Ribosomes play important roles in the synthesis of proteins. 2. Some ribosomes are found free in the cytoplasm of the cell. These ribosomes produce proteins that are to be used within the cytosol. Other ribosomes are attached to the ER. Proteins to be inserted into membranes or exported from the cell are produced by ribosomes that are attached to the ER. 3. The ER is a network of tubules and flattened sacs. It consists of channels that are used a paths along which molecules move from one part of the cell to another. 4. Rough ER has ribosomes attached to it. Rough ER is involved in the making of proteins that will be exported from the cell or inserted into the membranes of the cell. Smooth ER is so called because of the absence of ribosomes. The smooth ER is involved in the synthesis of steroids in gland cells, the regulation of calcium levels in muscle cells, and the breakdown of toxic substances in liver cells. 5. Amino acids are put together in the correct order by the ribosomes. Newly formed polypeptides are moved to the ER where the initial folding & shaping of the protein occurs. The protein is then moved to the Golgi for final folding & modifications. The Golgi prepares the protein for export from the cell.
8 Other Organelles 1. Golgi Apparatus: A stack of membranes in the cell that modifies, sorts, & packages proteins from the ER. Vacuole: Cell organelle that stores materials such as water, salts, proteins & carbohydrates. Lysosomes: Cell organelle filled with enzymes needed to break down certain materials in the cell. Cytoskeleton: A network of protein filaments within some cells that helps the cell maintain its shape and is involved in forms of cell movement. 2. The vacuole is much smaller in animal cells than in plant cells. The large central vacuole of a plant may take up as much as 90% of the cell s volume, pushing all other organelle up against the cell membrane. The pressure of water in a plant cell vacuole creates turgor pressure which aids the cell wall in structure and support.
9 Plant vs- Animal 1. Plant cells tend to be boxy and have a very definitive shape due to the presence of the cell wall. 2. Animal cells are more flexible & have not definitive shape due to the absence of a cell wall. 3. Plant cells need much structure & support to enable the plant to stand upright. Animal cells must be flexible to allow for movement. 4. Cell Wall: The cell wall is strong & inflexible. Its function is to give strength & support to the plant cell. Chloroplasts: Contain the green pigment chlorophyll & is the site of photosynthesis in a plant cell. Central Vacuole: A large vacuole filled primarily with water inside a plant cell. When filled with water, turgor pressure increases. This aids the cell wall in support. 5. These cell organelles carry out functions that occur only in plant cells.
10 Cell Internal Organization 1. Basic Eukaryotic Structure: Cell membrane: A lipid bilayer that serves as the outer boundary of the cell. Cytoplasm: The portion of the cell that lies in between the nucleus and the cell membrane. The cytoplasm contains the various organelles of the cell. Organelles: Structures with highly specialized functions that are found suspended in the cytoplasm of the cell. Nucleus: Contains nearly all of the cell s DNA which is the coded instructions for making the proteins of the cell. 2. Different jobs are carried out in the different areas of the factory, just like in the cell.
11 3. Nuclear membrane: A double membrane that encloses the nucleus. It is Porous to allow materials and messages to pass in & out. Chromatin: Granular material that consists of DNA tightly coiled around proteins. It condenses during cell division to form chromosomes. Chromosomes: A threadlike structure that contains the genetic information that is passed form one generation to the next. Nucleolus: The site of ribosome production. 4. Chloroplasts and mitochondria.
12 The Cell Membrane 1. The cell membrane regulates what enters and leaves the cell. It also provides protection and support to the cell. 2. A selective permeable membrane is a membrane that keeps out some molecules, but allows others to pass through. 3. This is a model of cell membrane structure representing the dynamic nature of membrane proteins and lipids. According to this model, the lipid bilayer behaves more like a fluid than a solid. Because of this fluidity, the lipids and proteins can move laterally within the lipid bilayer.
14 THE SIZE OF CELLS 1. Although there are exceptions, prokaryotes are generally smaller and less complex than eukaryotes. 2. The factor that limits the size of cells is the ratio between the volume and the surface area of the cell. 3. As a cell grows, its volume increases more rapidly than its surface area. 4. This is important because the nutrients, water and oxygen that a cell needs must enter through its surface. Therefore, as a cell grows larger, the surface area becomes too small to allow these materials to enter the cell quickly enough to meet the needs of the cell. 5.The smaller cell will be more efficient at moving in needed materials because it has a high surface area to volume ratio. As seen in the diagram below, materials will move farther into the smaller cell thereby supplying more of the cell with the materials the cell requires.
15 Surface Area to Volume Ratio: 1. V = 2cm * 2cm * 2cm = 8 cm (2cm * 2cm) = 24cm /8 = 3:1 ratio 4. Volume = (3cm) (3cm) (3cm) = 27cm3 5. Surface Area = 6 (3cm * 3cm) = 54cm /27 = 2:1 ratio 7. There is a decrease in the surface area to volume ratio as the cell increases in size. 8. As the surface area to volume ratio decreases, it takes longer for the cell to get the nutrients it needs and to get rid of its wastes. This might lead to starvation or poisoning.
16 Cell Division 1. There are 2 main reasons: a) The larger a cell becomes, the more demands the cell places on its DNA. As the cell grows too large, the DNA cannot keep up with the demands of running a larger cell. b) IF the cell grows too large, it will have trouble moving enough nutrients and wastes across the cell membrane. The larger the surface to volume ratio, the better. 2. Cell division is a process by lwhich a cell divides into 2 new daughter cells. 3.Mother cell original dividing cell Daughter Cell the result of the cell division.
17 4. a) MITOSIS Occurs in the SOMATIC (BODY) cells. b) MEIOSIS Occurs in the SEX Cells. 5. Prior to the divison of cells, all DNA must be replicated so that each new cell will receive the entire genome (entire genetic code)
18 The Cell Cycle 1. The cell cycle is the series of events that cells go through as they grow and divide. It is the life of the cells from the time it is first formed from a dividing parent cell until its own division into two cells. 2.
19 3. The 5 stages of the cell cycle are: G1: (INTERPHASE) A period of activity where cells do most of their growing. The cell increases in size and synthesizes new proteins and organelles. S: (INTERPHASE) Replication of DNA occurs. G2: (INTERPHASE) Molecules and organelles needed for cell division are produced. The cell is preparing to divide. Mitosis: (PMAT) The division of the nucleus. Cytokinesis: The division of the cytoplasm.
20 1. INTERPHASE
21 2. G1 phase: a period of activity where cells do most of their growing. The cell increases in size and synthesizes new proteins & organelles. S phase: Replication of DNA occurs. G2 phase: Molecules and organelles needed for cell division are produced. The cell is preparing to divide. 3. Centrosomes/centrioles are located just outside of the nucleus. 4. Cells spend most of their life in interphase.
22 Let s Draw the Stages of Mitosis:
23 Cell Division & Chromosome Number 1. Haploid is the term used to refer to a cell that contains only a single set of chromosomes 2. Diploid is the term used to refer to a cell that contains both sets of homologous chromosomes. 3. Sexual 4. Homologous chromosomes are chromosomes of a pair that carry the same genes at the same loci. They are similar in size, shape and the genes they carry. 5. All somatic cells (body cells) are diploid. 6. The gametes (sex cells) are haploid. 7. Egg and sperm must be haploid so that when the sperm fertilizes the egg, the diploid number will be restored in the zygote. 8. The cells that produce gametes undergo meiosis to produce haploid sex cells.
24 Meiosis 1. Meiosis occurs in cells that produce egg, sperm or spores. 2. Meiosis is a process of reduction division in which the # of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. The result is 4 haploid cells that will be either eggs, sperm or spores. 3. Meiosis I results in the separation of homologous chromosomes while Meiosis II results in the separation of sister chromatids.
25 1.At the end of telophase I. 2.A tetrad is a structure containing 4 chromatids that forms during meiosis. It is a group of 2 homologous chromosomes that have been replicated to form 4 chromatids. 3.Tetrads are formed during prophase I. 4.Crossing over is the process in which homologous chromosomes exchange portions of their chromatids during meiosis. It permits the exchange of genetic material between maternal & paternal chromosomes, producing a new combination of genetic material.
26 Which cells undergo this process? Number of daughter cells produced? MITOSIS Somatic Cells 2 4 Number of divisions? 1 2 What are the results of this division? Identical Cells Chromosome # of parent cell? 2N 2N Chromosome # of daughter cells? 2N Number of replications? 1 1 Number of chromosomes in daughters cells in comparison to the # in the mother cell? CONCEPT: COMPARING MITOSIS & MEIOSIS Same number Do tetrads form? No Yes Does crossing over occur? No Yes MEIOSIS Sex Cells Only Cells that are different 1N Half the number