1. PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 3 Cells: The Living Units: Part D

2. Copyright © 2010 Pearson Education, Inc. Cell Cycle Defines changes from formation of the cell until it reproduces Includes: Interphase Cell division (mitotic phase)

3. Copyright © 2010 Pearson Education, Inc. Interphase Period from cell formation to cell division Nuclear material called chromatin Four subphases: G 1 (gap 1)—vigorous growth and metabolism G 0 —gap phase in cells that permanently cease dividing S (synthetic)—DNA replication G 2 (gap 2)—preparation for division

4. Copyright © 2010 Pearson Education, Inc. Figure 3.31 G 1 Growth S Growth and DNA synthesis G 2 Growth and final preparations for division M G 2 checkpoint G 1 checkpoint (restriction point)

5. Copyright © 2010 Pearson Education, Inc. Figure 3.33 Centrosomes (each has 2 centrioles) Nucleolus Interphase Plasma membrane Nuclear envelope Chromatin Interphase

6. Copyright © 2010 Pearson Education, Inc. DNA Replication DNA helices begin unwinding from the nucleosomes Helicase untwists the double helix and exposes complementary chains The Y-shaped site of replication is the replication fork Each nucleotide strand serves as a template for building a new complementary strand

7. Copyright © 2010 Pearson Education, Inc. DNA Replication DNA polymerase only works in one direction Continuous leading strand is synthesized Discontinuous lagging strand is synthesized in segments DNA ligase splices together short segments of discontinuous strand

8. Copyright © 2010 Pearson Education, Inc. DNA Replication End result: two DNA molecules formed from the original This process is called semiconservative replication

9. Copyright © 2010 Pearson Education, Inc. Figure 3.32 Adenine Thymine Cytosine Guanine Old (template) strand Two new strands (leading and lagging) synthesized in opposite directions DNA polymerase Lagging strand Leading strand Free nucleotides Old strand acts as a template for synthesis of new strand Chromosome Helicase unwinds the double helix and exposes the bases Old DNA Replication fork

10. Copyright © 2010 Pearson Education, Inc. DNA Replication PLAY Animation: DNA Replication

11. Copyright © 2010 Pearson Education, Inc. Cell Division Mitotic (M) phase of the cell cycle Essential for body growth and tissue repair Does not occur in most mature cells of nervous tissue, skeletal muscle, and cardiac muscle

12. Copyright © 2010 Pearson Education, Inc. Cell Division Includes two distinct events: 1.Mitosis—four stages of nuclear division: Prophase Metaphase Anaphase Telophase 2.Cytokinesis—division of cytoplasm by cleavage furrow

13. Copyright © 2010 Pearson Education, Inc. Figure 3.31 G 1 Growth S Growth and DNA synthesis G 2 Growth and final preparations for division M G 2 checkpoint G 1 checkpoint (restriction point)

14. Copyright © 2010 Pearson Education, Inc. Cell Division PLAY Animation: Mitosis

15. Copyright © 2010 Pearson Education, Inc. Prophase Chromosomes become visible, each with two chromatids joined at a centromere Centrosomes separate and migrate toward opposite poles Mitotic spindles and asters form

16. Copyright © 2010 Pearson Education, Inc. Prophase Nuclear envelope fragments Kinetochore microtubules attach to kinetochore of centromeres and draw them toward the equator of the cell Polar microtubules assist in forcing the poles apart

17. Copyright © 2010 Pearson Education, Inc. Figure 3.33 Early mitotic spindle Early Prophase Centromere Aster Chromosome consisting of two sister chromatids Early Prophase

18. Copyright © 2010 Pearson Education, Inc. Figure 3.33 Spindle pole Kinetochore microtubule Polar microtubule Late Prophase Fragments of nuclear envelope Late Prophase

19. Copyright © 2010 Pearson Education, Inc. Metaphase Centromeres of chromosomes are aligned at the equator This plane midway between the poles is called the metaphase plate

20. Copyright © 2010 Pearson Education, Inc. Figure 3.33 Spindle Metaphase plate Metaphase

21. Copyright © 2010 Pearson Education, Inc. Anaphase Shortest phase Centromeres of chromosomes split simultaneously—each chromatid now becomes a chromosome Chromosomes (V shaped) are pulled toward poles by motor proteins of kinetochores Polar microtubules continue forcing the poles apart

22. Copyright © 2010 Pearson Education, Inc. Figure 3.33 Anaphase Daughter chromosomes Anaphase

23. Copyright © 2010 Pearson Education, Inc. Telophase Begins when chromosome movement stops The two sets of chromosomes uncoil to form chromatin New nuclear membrane forms around each chromatin mass Nucleoli reappear Spindle disappears

24. Copyright © 2010 Pearson Education, Inc. Cytokinesis Begins during late anaphase Ring of actin microfilaments contracts to form a cleavage furrow Two daughter cells are pinched apart, each containing a nucleus identical to the original

25. Copyright © 2010 Pearson Education, Inc. Figure 3.33 Contractile ring at cleavage furrow Nuclear envelope forming Nucleolus forming Telophase Telophase and Cytokinesis

26. Copyright © 2010 Pearson Education, Inc. Control of Cell Division “Go” signals: Critical volume of cell when area of membrane is inadequate for exchange Chemicals (e.g., growth factors, hormones, cyclins, and cyclin-dependent kinases (Cdks))

27. Copyright © 2010 Pearson Education, Inc. Control of Cell Division “Stop” signals: Contact inhibition Growth-inhibiting factors produced by repressor genes

28. Copyright © 2010 Pearson Education, Inc. Protein Synthesis DNA is the master blueprint for protein synthesis Gene: Segment of DNA with blueprint for one polypeptide Triplets of nucleotide bases form genetic library Each triplet specifies coding for an amino acid PLAY Animation: DNA and RNA

29. Copyright © 2010 Pearson Education, Inc. Figure 3.34 Nuclear pores mRNA Pre-mRNA RNA Processing Transcription Translation DNA Nuclear envelope Ribosome Polypeptide

30. Copyright © 2010 Pearson Education, Inc. Roles of the Three Main Types of RNA Messenger RNA (mRNA) Carries instructions for building a polypeptide, from gene in DNA to ribosomes in cytoplasm

31. Copyright © 2010 Pearson Education, Inc. Roles of the Three Main Types of RNA Ribosomal RNA (rRNA) A structural component of ribosomes that, along with tRNA, helps translate message from mRNA

32. Copyright © 2010 Pearson Education, Inc. Roles of the Three Main Types of RNA Transfer RNAs (tRNAs) Bind to amino acids and pair with bases of codons of mRNA at ribosome to begin process of protein synthesis

33. Copyright © 2010 Pearson Education, Inc. Transcription Transfers DNA gene base sequence to a complementary base sequence of an mRNA Transcription factor Loosens histones from DNA in area to be transcribed Binds to promoter, a DNA sequence specifying start site of gene to be transcribed Mediates the binding of RNA polymerase to promoter

34. Copyright © 2010 Pearson Education, Inc. Transcription RNA polymerase Enzyme that oversees synthesis of mRNA Unwinds DNA template Adds complementary RNA nucleotides on DNA template and joins them together Stops when it reaches termination signal mRNA pulls off the DNA template, is further processed by enzymes, and enters cytosol

35. Copyright © 2010 Pearson Education, Inc. Figure 3.35 RNA polymerase DNA Coding strand Template strandPromoter region Termination signal mRNA Template strand mRNA transcript Completed mRNA transcript Rewinding of DNA Coding strand of DNA DNA-RNA hybrid region The DNA-RNA hybrid: At any given moment, 16–18 base pairs of DNA are unwound and the most recently made RNA is still bound to DNA. This small region is called the DNA-RNA hybrid. Template strand Unwinding of DNA RNA nucleotides Direction of transcription Initiation: With the help of transcription factors, RNA polymerase binds to the promoter, pries apart the two DNA strands, and initiates mRNA synthesis at the start point on the template strand. Termination: mRNA synthesis ends when the termination signal is reached. RNA polymerase and the completed mRNA transcript are released. Elongation: As the RNA polymerase moves along the template strand, elongating the mRNA transcript one base at a time, it unwinds the DNA double helix before it and rewinds the double helix behind it. 1 2 3

36. Copyright © 2010 Pearson Education, Inc. Figure 3.35 step 1 RNA polymerase DNA Coding strand Template strand Promoter region Termination signal Initiation: With the help of transcription factors, RNA polymerase binds to the promoter, pries apart the two DNA strands, and initiates mRNA synthesis at the start point on the template strand. 1

37. Copyright © 2010 Pearson Education, Inc. Figure 3.35 step 2 mRNA Template strand mRNA transcript Elongation: As the RNA polymerase moves along the template strand, elongating the mRNA transcript one base at a time, it unwinds the DNA double helix before it and rewinds the double helix behind it. 2

38. Copyright © 2010 Pearson Education, Inc. Figure 3.35 step 3 RNA polymerase Completed mRNA transcript Termination: mRNA synthesis ends when the termination signal is reached. RNA polymerase and the completed mRNA transcript are released. 3

39. Copyright © 2010 Pearson Education, Inc. Figure 3.35 step 4 RNA polymerase mRNA Rewinding of DNA Coding strand of DNA DNA-RNA hybrid region The DNA-RNA hybrid: At any given moment, 16–18 base pairs of DNA are unwound and the most recently made RNA is still bound to DNA. This small region is called the DNA-RNA hybrid. Template strand Unwinding of DNA RNA nucleotides Direction of transcription

40. Copyright © 2010 Pearson Education, Inc. Figure 3.35 RNA polymerase DNA Coding strand Template strandPromoter region Termination signal mRNA Template strand mRNA transcript Completed mRNA transcript Rewinding of DNA Coding strand of DNA DNA-RNA hybrid region The DNA-RNA hybrid: At any given moment, 16–18 base pairs of DNA are unwound and the most recently made RNA is still bound to DNA. This small region is called the DNA-RNA hybrid. Template strand Unwinding of DNA RNA nucleotides Direction of transcription Initiation: With the help of transcription factors, RNA polymerase binds to the promoter, pries apart the two DNA strands, and initiates mRNA synthesis at the start point on the template strand. Termination: mRNA synthesis ends when the termination signal is reached. RNA polymerase and the completed mRNA transcript are released. Elongation: As the RNA polymerase moves along the template strand, elongating the mRNA transcript one base at a time, it unwinds the DNA double helix before it and rewinds the double helix behind it. 1 2 3

41. Copyright © 2010 Pearson Education, Inc. Translation Converts base sequence of nucleic acids into the amino acid sequence of proteins Involves mRNAs, tRNAs, and rRNAs

42. Copyright © 2010 Pearson Education, Inc. Genetic Code Each three-base sequence on DNA is represented by a codon Codon—complementary three-base sequence on mRNA

43. Copyright © 2010 Pearson Education, Inc. Figure 3.36 SECOND BASE UUG UUA UUC UUU Phe Leu CUG CUA CUC CUU Leu AUA AUC AUU Ile GUG GUA GUC GUU Val UCG UCA UCC UCU Ser CCG CCA CCC CCU Pro ACG ACA ACC ACU Thr GCG GCA GCC GCU Ala UAC UAU Tyr CAG CAA CAC CAU His Gln AAG AAA AAC AAU Asn Lys GAG GAA GAC GAU Asp Glu UGC UGU Cys Trp CGG CGA CGC CGU Arg AGG AGA AGC AGU Ser Arg GGG GGA GGC GGU Gly UAAStopUGAStop AUG Met or Start UAGStopUGG UCAG G A C U G A C U G A C U G A C U U C A G

44. Copyright © 2010 Pearson Education, Inc. Translation mRNA attaches to a small ribosomal subunit that moves along the mRNA to the start codon Large ribosomal unit attaches, forming a functional ribosome Anticodon of a tRNA binds to its complementary codon and adds its amino acid to the forming protein chain New amino acids are added by other tRNAs as ribosome moves along rRNA, until stop codon is reached

45. Copyright © 2010 Pearson Education, Inc. Figure 3.37 1 2 3 4 Leu Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. Amino acid tRNA Aminoacyl-tRNA synthetase G A A tRNA “head” bearing anticodon P site A site E site Ile Pro A A U U U C CC CG G G Large ribosomal subunit Small ribosomal subunit Direction of ribosome advance Portion of mRNA already translated Codon 15 Codon 16 Codon 17 Nucleus mRNA Released mRNA Nuclear membrane Nuclear pore RNA polymerase Template strand of DNA After mRNA synthesis in the nucleus, mRNA leaves the nucleus and attaches to a ribosome. Translation begins as incoming aminoacyl-tRNA recognizes the complementary codon calling for it at the A site on the ribosome. It hydrogen-bonds to the codon via its anticodon. As the ribosome moves along the mRNA, and each codon is read in sequence, a new amino acid is added to the growing protein chain and the tRNA in the A site is translocated to the P site. Once its amino acid is released from the P site, tRNA is ratcheted to the E site and then released to reenter the cytoplasmic pool, ready to be recharged with a new amino acid. The polypeptide is released when the stop codon is read. G A A U U A

46. Copyright © 2010 Pearson Education, Inc. Developmental Aspects of Cells All cells of the body contain the same DNA but are not identical Chemical signals in the embryo channel cells into specific developmental pathways by turning some genes off Development of specific and distinctive features in cells is called cell differentiation Elimination of excess, injured, or aged cells occurs through programmed rapid cell death (apoptosis) followed by phagocytosis

47. Copyright © 2010 Pearson Education, Inc. Theories of Cell Aging Wear and tear theory: Little chemical insults and free radicals have cumulative effects Immune system disorders: Autoimmune responses and progressive weakening of the immune response Genetic theory: Cessation of mitosis and cell aging are programmed into genes. Telomeres (strings of nucleotides on the ends of chromosomes) may determine the number of times a cell can divide.