1. Cell Signaling Animal cells communicate by:
Direct contact (gap junctions)
Secreting local regulators (growth factors, neurotransmitters)
Long distance (hormones)

3. 3 Stages of Cell Signaling:
Reception: Detection of a signal molecule (ligand) coming from outside the cell
Transduction: Convert signal to a form that can bring about a cellular response
Response: Cellular response to the signal molecule

4. 1. Reception
Binding between signal molecule (ligand) + receptor is highly specific.
Receptors found in:
Intracellular receptors (cytoplasm, nucleus)
hydrophobic or small
Eg. testosterone or nitric oxide (NO)
Plasma membrane receptor
water-soluble ligands

5. Plasma Membrane Receptors
G-Protein Coupled Receptor (GPCR)
Tyrosine Kinase
Ligand-Gated Ion Channels
7 transmembrane segments in membrane
Attaches (P) to tyrosine
Signal on receptor changes shape
G protein + GTP activates enzyme  cell response
Activate multiple cellular responses at once
Regulate flow of specific ions
(Ca2+, Na+)

6. G-Protein-Coupled Receptor

7. Receptor Tyrosine Kinase

8. Ligand-Gated Ion Channel

9. 2. Transduction
Cascades of molecular interactions relay signals from receptors  target molecules
Protein kinase: enzyme that phosphorylates and activates proteins at next level
Phosphorylation cascade: enhance and amplify signal

10. Second Messengers
small, nonprotein molecules/ions that can relay signal inside cell
Eg. cyclic AMP (cAMP) and Ca2+

11. 3. Response
Regulate protein synthesis by turning on/off genes in nucleus (gene expression)
Regulate activity of proteins in cytoplasm

12. Apoptosis = cell suicide
Cell is dismantled and digested
Triggered by signals that activate cascade of “suicide” proteins (caspase)
Protect neighboring cells from damage
Animal development & maintenance

13. Cell Cycle: life of a cell from its formation until it divides
Functions of Cell Division: Reproduction, Growth and Tissue Renewal

14. Genome = all of a cell’s genetic info (DNA)
Prokaryote: single, circular chromosome
Eukaryote: more than one linear chromosomes
Eg. Human:46 chromosomes, mouse: 40, fruit fly: 8

15. Each chromosome must be duplicated before cell division
Duplicated chromosome = 2 sister chromatids attached by a centromere

16. Somatic Cells Gametes Body cells
diploid (2n): 2 of each type of chromosome
Divide by mitosis
Humans: 2n = 46
Sex cells (sperm/egg)
Haploid (n): 1 of each type of chromosome
Divide by meiosis
Humans: n = 23

17. Phases of the Cell Cycle

18. Phases of the Cell Cycle
The mitotic phase alternates with interphase:
G1  S  G2  mitosis  cytokinesis
Interphase (90% of cell cycle)
G1 Phase: cell grows and carries out normal functions
S Phase: duplicates chromosomes
G2 Phase: prepares for cell division
M Phase (mitotic)
Mitosis: nucleus divides
Cytokinesis: cytoplasm divides

19. Mitosis: Prophase  Prometaphase  Metaphase  Anaphase  Telophase

20. Mitosis 1. Prophase Chromatin fibers condense and coil
Nucleoli disappear
Spindle (microtubules) begins to form
Centrosomes begin to move to opposite ends
2. Prometaphase
Nuclear envelope fragments
Microtubules invade nucleus
Kinetochores attach to microtubules

21. Prophase & Prometaphase

22. Mitotic spindle at metaphase
Kinetochore = proteins associated with DNA at centromere

23. 3. Metaphase
Chromosomes line up on metaphase plate at equator
Centrioles are at opposite poles (ends)
4. Anaphase (shortest phase)
Chromatids separate and pulled apart by motor proteins toward opposite ends of cell
Chromatids are called chromosomes now
Cell elongates

24. Metaphase & Anaphase

25. 5. Telophase
Nuclear membrane re-forms around chromosomes
Chromosomes less condensed
Cytokinesis
Cytoplasm of cell divided
Animal Cells: cleavage furrow
Plant Cells: cell plate forms

26. Cytokinesis in animal vs. plant cells

27. During anaphase Chromosomes walked to poles by motor proteins
Kinetochore microtubules shorten at ends as they depolymerize

28. Bacterial cells divide by Binary Fission

29. Cell Cycle Control System
Checkpoint = control point where stop/go signals regulate the cell cycle

30. Major Checkpoints G1 checkpoint (Most important!)
“Go”  completes whole cell cycle
“Stop”  cell enters nondividing state (G0 Phase)
Nerve, muscle cells stay at G0; liver cells called back from G0
G2 checkpoint
M Phase checkpoint
Anaphase does not begin unless chromatids are properly attached to spindle at metaphase plate

31. G1 Checkpoint

32. Internal Regulatory Molecules
Kinases (cyclin-dependent kinase, Cdk): protein enzyme controls cell cycle; active when connected to cyclin
Cyclins: proteins which attach to kinases (Cdk) to activate them; levels fluctuate in the cell cycle
3. MPF: maturation-promoting factor; specific Cdk which allows cells to pass G2 and go to M phase

33. External Regulatory Factors

34. External Regulatory Factors
Growth Factor: proteins released by other cells to stimulate cell division
Density-Dependent Inhibition: crowded cells normally stop dividing; cell-surface protein binds to adjoining cell to inhibit growth
Anchorage Dependence: cells must be attached to another cell or ECM to divide

35. Cancer Cells
Cancer: disorder in which cells lose the ability to control growth by not responding to regulation.
multistep process of about 5-7 genetic changes (for a human) for a cell to transform
loses anchorage dependency and density-dependency regulation
Normal Cells
Cancer Cells

36. Tumors = mass of abnormal cells
Benign tumor: lump of cells remain at original site
Malignant tumor: invasive - impairs functions of 1+ organs (called cancer)
Metastasis: cells separate from tumor and travel to other parts of body

37. Types of Reproduction ASEXUAL Produces clones (genetically identical)
Single parent
Little variation in population - only through mutations
Fast and energy efficient
Eg. budding, binary fission
SEXUAL
Meiosis produces gametes (sex cells)
2 parents: male/female
Lots of variation/diversity
Slower and energy consumptive
Eg. humans, trees

38. Asexual vs. sexual reproduction

39. Chromosomes Somatic (body) cell: 2n = 46 chromosomes
Each pair of homologous chromosomes includes 1 chromosome from each parent
Autosomes: 22 pairs of chromosomes that do not determine sex
Sex chromosomes: X and Y
Females: XX
Males: XY
Gametes (n=23): 22 autosomes + 1 sex chromosome
Egg: 22 + X
Sperm: 22 + X **or** 22 + Y

40. Homologous Chromosomes in a Somatic Cell

41. Karyotype: a picture of an organism’s complete set of chromosomes
Arranged from largest  smallest pair

42. Zygote divides by mitosis to make multicellular diploid organism
Life cycle: reproductive history of organism, from conception  production of own offspring
Fertilization and meiosis alternate in sexual life cycles
Meiosis: cell division that reduces # of chromosomes (2n  n), creates gametes
Fertilization: combine gametes (sperm + egg)
Fertilized egg = zygote (2n)
Zygote divides by mitosis to make multicellular diploid organism

43. Varieties of Sexual Life Cycles

44. Human Life Cycle

45. Animals

46. Alternation of Generations
Plant and some algae
Sporophyte (2n): makes haploid spores by meiosis
Spore  gametophyte by mitosis
Gametophyte (n): makes haploid gametes by mitosis

48. Fungi, protists, algae

49. Meiosis = reduction division
Cells divide twice
Result: 4 daughter cells, each with half as many chromosomes as parent cell

50. Meiosis I (1st division)
Interphase: chromosomes replicated
Prophase I:
Synapsis: homologous chromosomes pair up
Tetrad = 4 sister chromatids
Crossing over at the chiasmata
Metaphase I: Tetrads line up
Anaphase I:
Pairs of homologous chromosomes separate
(Sister chromatids still attached by centromere)
Telophase I & Cytokinesis:
Haploid set of chromosomes in each cell
Each chromosome = 2 sister chromatids
Some species: chromatin & nucleus reforms