3_Cell.ppt

2. Cell Organization • The cell is the basic structural and functional unit of life • Each cell is a highly organized unit (Table 3.1) – Plasma membrane: forms the outer boundary of the cell – Cellular organelles: each performs specific functions – Nucleus: contains the cell’s genetic material and directs cell activities – Cytoplasm: the material between the plasma membrane and nucleus

3. Fig. 3.1

4. Cell Functions 1. Metabolize and release energy • chemical reactions that occur within cells • release of energy in the form of heat helps maintain body temperature 2. Synthesize molecules • cells differ from each other because they synthesize different kinds of molecules 3. Provide a means of communication • achieved by chemical and electrical signaling 4. Reproduction and Inheritance • mitosis • meiosis

5. Plasma Membrane • Plays a dynamic role in cellular activity – encloses cell – supports the cell contents – a selective barrier that regulates what goes into and out of the cell – plays a role in communication between cells • Separates intracellular substances from extracellular substances – intracellular: inside cells – extracellular (intercellular): between cells

6. Fluid Mosaic Model • Lipid bilayer – double layer of lipids with imbedded, dispersed proteins • Bilayer consists mainly of phospholipids and cholesterol (20%) – Phospholipids have hydrophobic (nonpolar tails) and hydrophilic (polar heads) bipoles – Cholesterol gives the membrane added strength and flexibility

7. Fig. 3.2

8. Functions of Membrane Proteins Figure 3.4.2 • Protein molecules “float” among the phospholipid molecules • Functions – marker molecules – attachment proteins (cadherins and integrins) – transport proteins – receptor proteins – enzymes

9. Movement Through the Plasma Membrane • Ions and molecules move across plasma membranes by – diffusion – osmosis – mediated transport – vesicular transport

10. Diffusion • The movement of a solute from an area of higher concentration to an area of lower concentration within a solvent – at equilibrium, there is a uniform distribution of molecules • Terminology – Solution: any mixture of liquids, gases, or solids in which the substances are uniformly distributed with no clear boundary between the substances – A solute dissolves in a solvent to form a solution – Concentration gradient: the concentration difference between two points divided by the distance between those two points

11. Diffusion 1. Lipid-soluble molecules diffuse directly through the plasma membrane 2. Most non-lipid-soluble molecules and ions do not diffuse through the plasma membrane 3. Some specific non-lipid- soluble molecules and ions pass through membrane channels or other transport proteins

15. Diffusion

17. Osmosis • The diffusion of a solvent (water) across a selectively permeable membrane via diffusion. – through a specific channel protein (aquaporin) – or through the lipid bilayer • Terminology – Osmotic pressure: the force required to prevent the movement of water across a selectively permeable membrane – Isosmotic solutions: have the same concentration of solute particles as a reference solution – Hyperosmotic solutions: have a greater concentration of solute particles than a reference solution – Hyposmotic solutions: have a lesser concentration of solute particles than a reference solution

18. Fig. 3.5 Osmosis

20. Osmotic Concentration of Solutions a) A hypotonic solution with a low solute concentration results in swelling of the RBC placed into the solution. Water enters the cell by osmosis, and the RBC lyses (bursts). b) An isotonic solution with a concentration of solutes equal to that inside the cells results in a normal shaped RBC. Water moves into and out of the cell at the same rate, but there is no net water movement. c) A hypertonic solution, with a high solute concentration, causes shrinkage (crenation) of the RBC as water moves by osmosis out of the cell and into the hypertonic solution.

23. Osmotic Concentration of Solutions a) A hypotoinic solution with a low solute concentration results in swelling of the RBC placed into the solution. Water enters the cell by osmosis, and the RBC lyses (bursts). b) An isotonic solution with a concentration of solutes equal to that inside the cells results in a normal shaped RBC. Water moves into and out of the cell at the same rate, but there is no net water movement. c) A hypertonic solution, with a high solute concentration, causes shrinkage (crenation) of the RBC as water moves by osmosis out of the cell and into the hypertonic solution.

25. Mediated Transport • Process by which transport proteins mediate, or assist in, the movement of ions and molecules across the plasma membrane • Characteristics 1.Specificity: selectiveness 2.Competition: similar molecules or ions compete for a transport protein 3.Saturation: rate of transport cannot increase because all transport proteins are in use

26. Mediated Transport • Types of transport proteins 1. Channel proteins: form membrane channels (ion channels) 2. Carrier proteins: bind to ions or molecules and transport them – Uniport (facilitated diffusion) moves an ion or molecule down its concentration gradient – Symport moves two or more ions or molecules in the same direction – Antiport moves two or more ions or molecules in opposite directions 3. ATP-powered pumps: move ions or molecules against their concentration gradient using the energy from ATP – Secondary active transport uses the energy of one substance moving down its concentration gradient to move another substance across the plasma membrane

28. Fig. 3.7 Facilitated Diffusion

30. Sodium-Potassium Pump 1. Three sodium ions (Na+) and adenosine triphosphate (ATP) bind to the Na+-K+ pump, which is an ATP-powered pump. 2. The ATP breaks down to adenosine diphosphate (ADP) and a phosphate (P) and releases energy. That energy is used to power a shape change in the Na+-K+ pump. Phosphate remains bound to the Na+-K+-ATP binding site. 3. The Na+-K+ pump changes shape, and the Na+ are transported across the membrane. 4. The Na+ diffuses away from the Na+-K+ pump. 5. Two potassium ions (K+) bind to the Na+-K+ pump. 6. The phosphate is released from the Na+-K+ pump binding site. 7. The Na+-K+ pump resumes its original shape, transporting K+ across the membrane, and the K+ diffuse away from the pump. The Na+-K+ pump can again bind to Na+ and ATP.

31. Sodium-Potassium Pump 1. Three sodium ions (Na+) and adenosine triphosphate (ATP) bind to the Na+-K+ pump, which is an ATP-powered pump. 2. The ATP breaks down to adenosine diphosphate (ADP) and a phosphate (P) and releases energy. That energy is used to power a shape change in the Na+-K+ pump. Phosphate remains bound to the Na+-K+-ATP binding site. 3. The Na+-K+ pump changes shape, and the Na+ are transported across the membrane. 4. The Na+ diffuses away from the Na+-K+ pump. 5. Two potassium ions (K+) bind to the Na+-K+ pump. 6. The phosphate is released from the Na+-K+ pump binding site. 7. The Na+-K+ pump resumes its original shape, transporting K+ across the membrane, and the K+ diffuses away from the pump. The Na+-K+ pump can again bind to Na+ and ATP.

37. Secondary Active Transport • Symport of Na+ and Glucose 1. A Na+-K+ pump (ATP-powered pump) maintains a concentration of Na+ that is higher outside the cell than inside. 2. Sodium ions move back into the cell through a carrier protein (symporter) that also moves glucose. The concentration gradient for Na+ provides energy required to move glucose against its concentration gradient. Fig. 3.9

39. Vesicular Transport • Transport of large particles and macromolecules across plasma membranes – Endocytosis: the movement of materials into cells by the formation of a vesicle • Phagocytosis: the movement of solid material into cells • Pinocytosis: the uptake of small droplets of liquids and the materials in them • Receptor-mediated endocytosis: involves plasma membrane receptors attaching to molecules that are then taken into the cell – Exocytosis: the secretion of materials from cells by vesicle formation

40. Phagocytosis Fig. 3.10

42. Receptor-Mediated Endocytosis 1. Receptors in the plasma membrane bind to molecules to be taken into the cell 2. The receptors and the bond molecules are taken into the cell as a vesicle begins to form 3. The vesicle fuses and separates from the plasma membrane Fig. 3.11

46. Exocytosis 1. A secretory vesicle moves toward the plasma membrane 2. The membrane of the secretory vesicle fuses with the plasma membrane 3. The secretory vesicle’s contents are released into the extracellular fluid Fig. 3.12

51. Cytoplasm • The material between the plasma membrane and the nucleus – Half cytosol • Consists of a fluid part (the site of chemical reactions), the cytoskeleton, and cytoplasmic inclusions – The cytoskeleton supports the cell and enables cell movements » Microtubules – provide support, aid in cell division, and are components of organelles » Actin filaments – support the plasma membrane and define the shape of the cell » Intermediate filaments – provide mechanical support to teh cell – Half organelles • Cytoplasmic Inclusions are aggregates of chemicals either produced by the cell or taken in by the cell (lipids, glycogen, hemoglobin, melanin)

52. Fig. 3.13 Cytoskeleton

53. Cytoplasmic Organelles • Specialized subcellular structures with specific functions • Membranous – Mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus • Nonmembranous – Centrioles and ribosomes

54. Nucleus • The nuclear envelope consists of two separate membranes with nuclear pores – Encloses jellylike nucleoplasm, which contains essential solutes • DNA and associated proteins are found inside the nucleus – DNA is the hereditary material of the cell and controls the activities of the cell – Contains the genetic library with blueprints for nearly all cellular proteins – Dictates the kinds and amounts of proteins to be synthesized – Between cell divisions DNA is organized as chromatin – During cell division chromatin condenses to form chromosomes consisting of two chromatids connected by a centromere

55. Fig. 3.14 Nucleus

56. Fig. 3.15 Chromosome Structure

57. Nucleoli and Ribosomes • Nucleoli: dark-staining spherical bodies within the nucleus – Consist of RNA and proteins – Produces ribosomal ribonucleic acid (rRNA) – Site of ribosomal subunit assembly • Ribosomes: sites of protein synthesis – Free ribosomes are not attached to any organelles • synthesize proteins used inside the cell – Attached ribosomes are part of a network of membranes called the rough endoplasmic reticulum (RER) • produce proteins that are secreted from the cell

58. Fig. 3.16 Production of Ribosomes

59. Endoplasmic Reticulum (ER) • Series of membranes forming sacs and tubules that extend from the outer nuclear membrane into the cytoplasm • Two varieties: rough ER and smooth ER – Rough ER (RER) • Studded with ribosomes • Major site of protein synthesis – Smooth ER (SER) • Does not have ribosomes attached • Major site of lipid and carbohydrate synthesis – Catalyzes the following reactions in various organs of the body » Liver: lipid and cholesterol metabolism, breakdown of glycogen and along with the kidneys, detoxifiy drugs » Testes: synthesis of steroid-based hormones » Intestinal cells: absorption, synthesis, and transport of fats » Skeletal and cardiac muscle: storage and release of calcium

60. Endoplasmic Reticulum (ER) Fig. 3.17

61. Golgi Apparatus • Series of closely packed membranous sacs that collect, package, and distribute proteins and lipids produced by the ER – Secretory vesicles: small, membrane-bound sacs that transport material from the golgi apparatus to the exterior of the cell Fig. 3.18

62. Function of the Golgi Apparatus 1. Some proteins are produced at ribosomes on the surface of the RER and are transferred into the cisterna as they are produced 2. The proteins are surrounded by a vesicle that forms from the membrane of the ER 3. This transport vesicle moves from the ER to the Golgi apparatus, fuses with its membrane, and releases the proteins into its cisterna 4. The Golgi apparatus concentrates and in some cases, modifies the proteins into glycoproteins or lipoproteins 5. The proteins are packaged into vesicles that form from the membrane of the Golgi apparatus 6. Some vesicles, such as lysosomes, contain enzymes that are used within the cell 7. Secretory vesicles carry proteins to the plasma membrane, where the proteins are secreted from the cell by exocytosis 8. Some vesicles contain proteins that become part of the plasma membrane Fig. 3.19

71. Lysosomes • Spherical membranous bags containing digestive enzymes – Digest ingested bacteria, viruses, and toxins – Degrade nonfunctional organelles – Breakdown glycogen and release thyroid hormone – Breakdown non-useful tissue – Breakdown bone to release Ca2+ – Secretory lysosomes are found in white blood cells, immune cells, and melanocytes

72. Action of Lysosomes 1. A vesicle forms around material outside the cell 2. The vesicle is pinched off from the plasma membrane and becomes a separate vesicle inside the cell 3. A lysosome is pinched off the Golgi apparatus 4. The lysosome fuses with the vesicle Fig. 3.20 5. The enzymes from the lysosome mix with the material in vesicle, and the enzymes digest the material

79. Peroxisomes • Membranous sacs containing oxidases and catalases – Breakdown fatty acids, amino acids, and hydrogen peroxide – Detoxify harmful or toxic substances – Neutralize dangerous free radicals • Free radicals: highly reactive chemicals with unpaired electrons (i.e., O2 –)

80. Mitochondria Fig. 3.21 • The major sites of the production of ATP (the major energy source for cells) via aerobic cellular respiration • Have a smooth outer membrane and an inner membrane that is infolded to produce cristae • Contain their own DNA, can produce some of their own proteins, and can replicate independently of the cell

81. Centrioles and Spindle Fibers • Centrioles: cylindrical organelles located in the centrosome – Pinwheel array of nine triplets of microtubules – Centrosome: a specialized zone of the cytoplasm • the site of microtubule formation – Microtubules called spindle fibers extend out in all directions from the centrosome • Spindle fibers are involved in the separation of chromosomes during cell division – Form the bases of cilia and flagella Fig. 3.22

82. Cilia, Flagella, and Microvilli • Cilia move substances over the surface of cells • Flagella are much longer than cilia and propel sperm cells • Microvilli increase the surface area of cell and aid in absorption and secretion

83. Protein Synthesis • DNA serves as master blueprint for protein synthesis • DNA controls enzyme production and cell activity is regulated by enzymes (Proteins) • Genes are segments of DNA carrying instructions for a polypeptide chain • Triplets of nucleotide bases form the genetic library • Each triplet specifies coding for an amino acid

84. Protein Synthesis • Two step process – Transcription • cell makes a copy of the gene necessary to make a particular protein: messenger RNA (mRNA) • mRNA then travels from the nucleus to the ribosomes where the information is translated into a protein – Translation • requires both mRNA and transfer RNA (tRNA) • tRNA brings the amino acids necessary to synthesize the protein to the ribosome

85. Overview of Protein Synthesis 1. DNA contains the information necessary to produce proteins 2. Transcription of one DNA strand results in mRNA, which is a complementary copy of the information in the DNA strand needed to make a protein 3. The mRNA leaves the nucleus and goes to a ribosome 4. Amino acids, the building blocks of proteins, are carried to the ribosome by tRNAs 5. In the process of translation, the information contained in mRNA is used to determine the number, kinds, and arrangement of amino acids in the polypeptide chain Fig. 3.23

91. Transcription • Synthesis of mRNA, tRNA, and rRNA based on the nucleotide sequence in DNA – Messenger RNA (mRNA) – carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm – Transfer RNAs (tRNAs) – bound to amino acids base pair with the codons of mRNA at the ribosome to begin the process of protein synthesis – Ribosomal RNA (rRNA) – a structural component of ribosomes

92. Transcription 1. The strands of the DNA molecule separate from each other. One DNA strand serves as a template for mRNA synthesis 2. Nucleotides that will form mRNA pair with DNA nucleotides according to the base-pair combinations shown in the key at the top of the figure. Thus, the sequence of nucleotides in the template DNA strand (purple) determines the sequence of nucleotides in mRNA (grey). RNA polymerase (the enzyme is not shown) joins the nucleotides of mRNA together 3. As nucleotides are added, an mRNA molecule is formed Fig. 3.24

93. Transcription: RNA Polymerase • An enzyme that oversees the synthesis of RNA • Unwinds the DNA template • Adds complementary ribonucleoside triphosphates on the DNA template • Joins these RNA nucleotides together • Encodes a termination signal to stop transcription

94. Transcription • Posttranscriptional processing modifies mRNA before it leaves the nucleus by removing introns (non-coding) and then splicing exons (coding) together with enzymes called spliceosomes – Functional mRNA consists only of exons • Alternative splicing produces different combination of exons, allowing one gene to produce more than one type of protein

97. Translation • Synthesis of proteins in response to the codons of mRNA – Codon: a set of 3 nucleotides that codes for 1 amino acid during translation – Anticodon: part of tRNA and consists of three nucleotides and is complementary to a particular codon of mRNA • mRNA moves through the nuclear pores to ribosomes • tRNA, which carries amino acids, interacts at the ribosome with mRNA. The anticodons of tRNA bind to the codons of mRNA, and the amino acids are joined to form a protein

98. Translation 1. To start protein synthesis, a ribosome binds to mRNA. The ribosome has two binding sites for tRNA with its amino acid. Note that the first codon to associate with a tRNA is AUG, the start codon, which codes for methionine. The codon of mRNA and the anitcodon of tRNA are aligned and joined. The other tRNA binding site is open Fig. 3.25

99. Translation 1. To start protein synthesis, a ribosome binds to mRNA. The ribosome has two binding sites for tRNA with its amino acid. Note that the first codon to associate with a tRNA is AUG, the start codon, which codes for methionine. The codon of mRNA and the anitcodon of tRNA are aligned and joined. The other tRNA binding site is open 2. By occupying the open tRNA binding site, the next tRNA is properly aligned with mRNA and with the other tRNA Fig. 3.25

100. Translation 1. To start protein synthesis, a ribosome binds to mRNA. The ribosome has two binding sites for tRNA with its amino acid. Note that the first codon to associate with a tRNA is AUG, the start codon, which codes for methionine. The codon of mRNA and the anitcodon of tRNA are aligned and joined. The other tRNA binding site is open 2. By occupying the open tRNA binding site, the next tRNA is properly aligned with mRNA and with the other tRNA 3. An enzyme within the ribosome catalyzes a synthesis reaction to form a peptide bond between the amino acids. Note that the amino acids are now associated with only one of the tRNAs Fig. 3.25

101. Translation 3. An enzyme within the ribosome catalyzes a synthesis reaction to form a peptide bond between the amino acids. Note that the amino acids are now associated with only one of the tRNAs 4. The ribosome shifts position by three nucleotides. The tRNA without the amino acid is released from the ribosome, and the tRNA with the amino acids takes its position. A tRNA binding site is left open by the shift. Additional amino acids can be added by repeating steps 2 through 4 Fig. 3.25

102. Translation 3. An enzyme within the ribosome catalyzes a synthesis reaction to form a peptide bond between the amino acids. Note that the amino acids are now associated with only one of the tRNAs 4. The ribosome shifts position by three nucleotides. The tRNA without the amino acid is released from the ribosome, and the tRNA with the amino acids takes its position. A tRNA binding site is left open by the shift. Additional amino acids can be added by repeating steps 2 through 4 5. Eventually a stop codon in the mRNA, such as UAA, ends the process of translation. At this point, the mRNA and polypeptide chain are released from the ribosome. 6. Multiple ribosomes attach to a single mRNA to form a polyribosome. As the ribosomes move down the mRNA, proteins attached to the ribosomes lengthen and eventually detach from the mRNA Fig. 3.25

103. Translation 1. To start protein synthesis, a ribosome binds to mRNA. The ribosome has two binding sites for tRNA with its amino acid. Note that the first codon to associate with a tRNA is AUG, the start codon, which codes for methionine. The codon of mRNA and the anitcodon of tRNA are aligned and joined. The other tRNA binding site is open 2. By occupying the open tRNA binding site, the next tRNA is properly aligned with mRNA and with the other tRNA 3. An enzyme within the ribosome catalyzes a synthesis reaction to form a peptide bond between the amino acids. Note that the amino acids are now associated with only one of the tRNAs 4. The ribosome shifts position by three nucleotides. The tRNA without the amino acid is released from the ribosome, and the tRNA with the amino acids takes its position. A tRNA binding site is left open by the shift. Additional amino acids can be added by repeating steps 2 through 4 5. Eventually a stop codon in the mRNA, such as UAA, ends the process of translation. At this point, the mRNA and polypeptide chain are released from the ribosome. 6. Multiple ribosomes attach to a single mRNA to form a polyribosome. As the ribosomes move down the mRNA, proteins attached to the ribosomes lengthen and eventually detach from the mRNA Fig. 3.25

104. Information Transfer from DNA to RNA • DNA triplets are transcribed into mRNA codons by RNA polymerase • Codons base pair with tRNA anticodons at the ribosomes • Amino acids are peptide bonded at the ribosomes to form polypeptide chains • Start and stop codons are used in initiating and ending translation

105. Cell Division • Cell division that occurs by mitosis produces new cells for growth and tissue repair • Cell division that occurs by meiosis produces gametes (sex cells). – Sperm cells in males – Oocytes (egg cells) in females

107. Cell Division • Chromosomes – Somatic cells have a diploid number of chromosomes – Gametes have a haploid number – In humans, the diploid number is 46 (23 pairs) and the haploid number is 23 • Twenty-two pairs of autosomal chromosomes • One pair of sex chromosomes – Females XX – Males XY • DNA replicates during interphase, the time between cell division

108. Replication of DNA 1. The strands of the DNA molecule separate from each other 2. Each old strand (dark purple) functions as a template on which a new, complementary strand (light purple) is formed. The base-pairing relationship between nucleotides determines the sequence of nucleotides in the newly formed strands 3. Two identical DNA molecules are produced Fig. 3.26

109. Replication of a Chromosome 1. The DNA of a chromosome is dispersed as chromatin 2. The DNA molecule unwinds and each strand of the molecule is replicated 3. During mitosis the chromatin from each replicated DNA strand condenses to form a chromatid. The chromatids are joined at the centromere to form a single chromosome 4. The chromatids separate to form two new, identical chromosomes. The chromosomes will unwind to form chromatin in the nuclei of the two daughter cells Fig. 3.26

116. Mitosis and Cytokinesis Fig. 3.28 1. Interphase is the time between cell divisions. DNA is found as thin threads of chromatin in the nucleus. DNA replication occurs during interphase. Organelles, other than the nucleus, duplicate during interphase 2. In prophase, the chromatin condenses into chromosomes. The centrioles move to the opposite ends of the cell, and the nucleolus and the nuclear envelope disappear. Microtubules form near the centrioles and project in all directions. Spindle fibers, project toward an invisible line called the equator and overlap with fibers from opposite centrioles. 3. In metaphase, the chromosomes align in the center of the cell in association with the spindle fibers. Some spindle fibers are attached to kinetochores in the centromere of each chromosome 4. In anaphase, the chromatids separate, and each chromatid is then referred to as a chromosome. Thus, the chromosome number is double, and there are two identical sets of chromosomes. The chromosomes, assisted by the spindle fibers, move toward the centrioles at each end of the cell. Separation of the chromatids signals the beginning of anaphase, and, by the time anaphase has ended, the chromosomes have reached the poles 5. In telophase, migration of each set of chromosomes is complete. The chromosomes unravel to become less distinct chromatin threads. The nuclear envelope forms from the endoplasmic reticulum. The nucleoli form, and cytokinesis continues to form two cells 6. Mitosis is complete, and a new interphase begins. The chromosomes have unraveled to become chromatin. Cell division has produced two daughter cells, each with DNA that is identical to the DNA of the parent cell

117. Interphase Fig. 3.28 1. Interphase is the time between cell divisions. DNA is found as thin threads of chromatin in the nucleus. DNA replication occurs during interphase. Organelles, other than the nucleus, duplicate during interphase

118. Prophase Fig. 3.28 2. In prophase, the chromatin condenses into chromosomes. The centrioles move to the opposite ends of the cell, and the nucleolus and the nuclear envelope disappear. Microtubules form near the centrioles and project in all directions. Spindle fibers, project toward an invisible line called the equator and overlap with fibers from opposite centrioles.

119. Metaphase Fig. 3.28 3. In metaphase, the chromosomes align in the center of the cell in association with the spindle fibers. Some spindle fibers are attached to kinetochores in the centromere of each chromosome

120. Anaphase Fig. 3.28 4. In anaphase, the chromatids separate, and each chromatid is then referred to as a chromosome. Thus, the chromosome number is double, and there are two identical sets of chromosomes. The chromosomes, assisted by the spindle fibers, move toward the centrioles at each end of the cell. Separation of the chromatids signals the beginning of anaphase, and, by the time anaphase has ended, the chromosomes have reached the poles

121. Telophase and Cytokinesis Fig. 3.28 5. In telophase, migration of each set of chromosomes is complete. The chromosomes unravel to become less distinct chromatin threads. The nuclear envelope forms from the endoplasmic reticulum. The nucleoli form, and cytokinesis continues to form two cells

122. Mitosis Fig. 3.28 6. Mitosis is complete, and a new interphase begins. The chromosomes have unraveled to become chromatin. Cell division has produced two daughter cells, each with DNA that is identical to the DNA of the parent cell

123. Mitosis and Cytokinesis Fig. 3.28 1. Interphase is the time between cell divisions. DNA is found as thin threads of chromatin in the nucleus. DNA replication occurs during interphase. Organelles, other than the nucleus, duplicate during interphase 2. In prophase, the chromatin condenses into chromosomes. The centrioles move to the opposite ends of the cell, and the nucleolus and the nuclear envelope disappear. Microtubules form near the centrioles and project in all directions. Spindle fibers, project toward an invisible line called the equator and overlap with fibers from opposite centrioles. 3. In metaphase, the chromosomes align in the center of the cell in association with the spindle fibers. Some spindle fibers are attached to kinetochores in the centromere of each chromosome 4. In anaphase, the chromatids separate, and each chromatid is then referred to as a chromosome. Thus, the chromosome number is double, and there are two identical sets of chromosomes. The chromosomes, assisted by the spindle fibers, move toward the centrioles at each end of the cell. Separation of the chromatids signals the beginning of anaphase, and, by the time anaphase has ended, the chromosomes have reached the poles 5. In telophase, migration of each set of chromosomes is complete. The chromosomes unravel to become less distinct chromatin threads. The nuclear envelope forms from the endoplasmic reticulum. The nucleoli form, and cytokinesis continues to form two cells 6. Mitosis is complete, and a new interphase begins. The chromosomes have unraveled to become chromatin. Cell division has produced two daughter cells, each with DNA that is identical to the DNA of the parent cell

125. Differentiation • Process by which cells develop specialized structures and functions • All the cells in an individual’s body contain the same amount and type of DNA because they resulted from mitosis • Differentiation results from the selective activation and inactivation of segments of DNA in each different cell type

3_Cell.ppt

More Related Content

What's hot (12)

Similar to 3_Cell.ppt (20)

More from PaulMarkPilar2 (8)

Recently uploaded (20)

3_Cell.ppt