1_cell_iv
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CELL IV(30% of Block 2 Test)
Cell Locomotion: Reasons for locomotion of cells
Embryonic development. (Organogenesis and morphogenesis)
Physiological/Pathological Leucocyte margination Platelet adhesion Wound healing Metastasis (Cancer)
Physiological/Pathological Leukocyte margination:
Adhesion to endothelial cells Platelet Adhesion
Platelets adhere, degranulate, initiate clotting Wound Healing
Integrins cell adhesion cell movement and migration.
enable epithelial cells to migrate during wound closure aid signal transduction
epidermal cells migrate into the wound
changing the number, type, and distribution of integrins in the cells Metastasis:
Proliferation of the primary tumor; intravasation
invasion of the blood or lymphatic circulation Structures involved for movement
Lamellipodium by Rac (Rho family of GTP-Binding proteins) undulating motion,
ruffled appearance. Seen in fibroblasts
Filopodia-activated by Cdc42 (Rho family of GTP-Binding proteins) actin filaments. extension & retraction movements. Seen in growth cones of axons.
Cell Locomotion involves three processes: Lamellipodia
extend from front of the cell. Attachment:
Actin cytoskeleton makes contact with substrate. Traction:
Body of the cell moves forward. Cell Cycle:
Cell Division: Key Roles:
Genome: cell’s genetic information Somatic (body cells) cells Gametes (reproductive cells): sperm and egg cells Chromosomes: DNA molecules Diploid (2n): 2 sets of chromosomes Haploid (1n): 1 set of chromosomes Chromatin: DNA-protein complex Chromatids: replicated strands of a chromosome Centromere: narrowing “waist” of sister chromatids Telomere: ends of the chromosomes Mitosis: nuclear division Cytokinesis: cytoplasm division Meiosis: gamete cell division
Number of Chromosomes: Haploid (23) – ‘n’ number of chromosomes Diploid (46) – ‘2n’ number of chromosomes
Amount of DNA with respect to cell division: Haploid – ‘N’ amount of DNA Diploid – ‘2N’ amount of DNA
Interphase: All somatic cells: 2n,2N.
(n = the number of sets of chromosomes, N = the amount of DNA)
Interphase (2n,2N→2n,4N): Phase during which cells do not undergo division .
Mitosis: Prophase
chromatin condenses into chromosomes (visible) Nucleolus and the nuclear envelope begin to disappear Kinetochores will develop as microtubule organizing centers Prometaphase
Begins when the nuclear envelope disappears Chromosomes are randomly dispersed in the cytoplasm Chromosome microtubules attach to kinetochores
Kinetochores attach to spindle microtubules Kinetochore microtubules
Metaphase Chromosomes align at equator, homologs align independently of each other
Anaphase Anaphase promoting complex
APC inhibits securin Securin is involved in cohesion of sister chromatids APC is a target for anti-cancer therapy
Spindle elongates Shortening of microtubules—movement of chromosomes Chromosomes are split in synchrony Chromatids separate at the centromere Daughter chromosomes move to opposite poles of the cell Cleavage furrow begins to form
Contractile ring-- actin filaments Telophase
Each set of chromosomes reaches the pole Deepening of the cleavage furrow Cytokinesis Nuclear envelope is reestablished Nucleoli reappear Daughter cells enlarge Chromosomes disperse to form the typical interphase nucleus
Meiosis Prophase (subdivided into 5 stages)
Prophase I: Leptotene Chromosomes appear as threads (diploid number).
homologous chromosomes are unpaired Prophase I: Zygotene
Homologous chromosomes paternal and maternal arrange lengthwise (pre-synapsis)
Prophase I: Pachytene Chromosomes become shorter and thicker in appearance most easily identifiable stage of primary spermatocytes. Chromosomes are completely paired Synaptonaemal complex (SC): synapsis
Prophase I: Diplotene Dissolution of synaptonemal complex Chromosomes are shorter Homologous chromosomes repelling one another “Crossing Over” of chromatids arms -- Chiasmata chromosomal separation
chromosomal abnormalities may occur at this time Prophase I: Diakinesis
Continued separation of chromosomes nuclear envelope and nucleolus disappears.
Metaphase I
Anaphase I Telophase I 2nd Meiotic Division
Prophase II – Interkinesis without duplication of the chromosomes
Metaphase II Anaphase II Telophase II
Cell Cycle G1-phase (2N DNA, 46 chr)
Continue dividing variations in length of G1 phase
Or exit dividing. Enter GO phase (2N DNA, 46 chr)
Neurons are usually in G0 phase S-phase (2N / 4N, 46 chr)
DNA replication G2-phase (4N (tetraploid))
reached following completion of DNA replication. M-phase (4N)
mitotic phase Flow Cytometry
Thymidine incorporation 3HT=>autoradiograph technique
cell cycle based on the intensity of fluorescence of the nuclei DNA content of 2N
Most Cells large peak on the flow histogram.
DNA content of 4N 3.4% of the cell cycle
peak is much smaller Cell Cycle Checkpoint Genes (Rare genetic mistakes)
If a genetic mistake (i.e. exposure of a cell to radiation ) cell cycle checkpoint genes
prevent cells from dividing into two daughter cells. G1 Checkpoint
Adequate cell size Sufficient nutrients Growth factors present
G2 Checkpoint Adequate cell size Successful chromosomal replication
Metaphase Checkpoint All chromosomes attached to mitotic spindle
Cell Cycle Regulators Cyclins (rise and fall with the stages of the cell cycle)
G1 phase cyclin D S-phase cyclins E and A
mitotic phase cyclin B Cyclin-dependent kinases (Cdks)
levels in the cell remain fairly stable bind the appropriate cyclin for activation
G1 phase Cdk4 S-phase Cdk2 M-phase Cdk (Cdk1)
Phospholates protein substrates control processes in the cell cycle
Anaphase-promoting complex (APC). also called the cyclosome or APC/C triggers destruction of the cohesins
degrades the mitotic (B) cyclins sister chromatids to separate
Growth Factors: Involved in G1 checkpoint
Retinoblastoma protein (Rb) Tumor suppressor protein Bound to E2F (Transcription factor)
Shuts down cell cycle Growth Factors activates cyclin/cdk complex
Phospholates Rb E2F is released
E2F stimulates S phase protein production Cell Cycle Checkpoint Regulation:
p53 – pro-apoptotic tumor-suppressor gene, Protein p53
Minor DNA damage halts the cell cycle until repaired.
Major DNA damage cannot be repaired triggers apoptosis.
Protection against cancer - acts as a tetramer Single mutation can result in a dominant negative >half of human cancers
p53 mutations no functioning p53 protein.
G1 response to DNA damage. DNA damage blocks entrance into S phase.
Phosphorylation of active ATM activates pathways to G1 arrest
Chk2 phosphorylates Cdc25A inactivation and inability to activate CDK2
Phosphorylation of p53 protein transcription of a number of genes
DNA repair and cell survival. Phosphorylation and inactivation of Mdm2
Stabilization of p53. p16INK4a (product of the tumor suppressor gene INK4a
Inhibits cyclin-dependent kinase Cdk4. Increasing amounts of p16INK4a with age
Reduces the risk of uncontrolled mitosis, i.e., becoming a cancer. Deletions and other mutations of p16INK4a are found in a variety of
cancers However, ability to reproduce and thus replace lost or damaged tissue
diminishes. Mutations Causing Loss of Growth-Inhibiting and Cell-Cycle Controls
Normally a balance between growth-stimulating and growth- inhibiting signaling pathways.
Overproduction of cyclin D, a positive regulator, or loss of the negative regulators p16 or Rb, commonly occurs in human cancers.
Micro RNAs (mi RNA ) Regulate oncogene expression Transcribed into RNA (but not protein) mRNA complementary Noncoding intron regions of DNA Expression of miRNA altered in tumors
over expression of oncogenes Molecular Biology of Cancer
Proto-oncogene Non- mutated normal cellular genes
Oncogene Mutated genes responsible for cancer development
usually become dominant Examples
Translocation Chromosome fragments rejoin incorrectly
Philadelphia chromosome (Bcr-Abl gene) give rise to chronic myelogenous leukemia (CML) Gleevec / imatinib mesylate
Amplification Increased copies of proto-oncogenes
high expression of the normal protein Proto-oncogene point mutation
protein product more active more resistant to degradation
Tumor suppressor genes, (typically recessive) Negative regulators of the cell cycle (Rb, p16). Receptors or signal transducers that inhibit proliferation (TGFβ). Checkpoint mutations (p53). Proteins involved in DNA repair XP, FA, BRCA) proteins that reverse or prevent DNA damage (caretaker genes)
As multiple genetic abnormalities occur, multiple sub-clones develop or evolve. Eventually, one of these sub-clones may acquire the necessary combination of genetic abnormalities to become a cancer
Chromosomal errors, I Nondisjunction :
Chromosomes do not separate properly during meiosis I or sister chromatids fail to separate during meiosis II
Maternal age effect Older women have higher incidences Eggs being held in a meiotic block (meiosis II) for an extended period of time
Paternal age effect Older men can produce sperm with abnormal chromosome numbers
Aneuploidy: chromosome number is abnormal Monosomy~ missing chromosome
Turner Syndrome Lacks X or Y sex chromosome ~45 XO Exhibit female phenotype; sterile Short stature, webbed neck; high arched palate Cognitive defects (i.e., affects learning) Occurrence: 1 in 2500 females
Most cases of monosomy are not viable Trisomy ~ extra chromosome
Down syndrome-trisomy 21 Extra copy of chromosome 21 ~ 47,XX +21 or 47, XY +21
Klinefelter Syndrome: 47, XXY Male with extra X chromosome
Polyploidy~ extra sets of chromosomes 69 XXX, XXY, or XYY
Chromosomal errors II Deletion: removal of a chromosomal segment Duplication: repeats a chromosomal segment Inversion: segment reversal in a chromosome Translocation: movement of a chromosomal segment to another
Genomic Imprinting Parental effect on gene expression Identical alleles have different effects on offspring
zygote via the ovum or via the sperm. Fragile X syndrome
high prevalence retardation in males Mechanisms of cellular homeostasis / cell death
Proteosomes Cellular homeostasis, and in human disease Enzymes of the ubiquitin (non-lysosomal) protein degradation
ATP-dependent Degradation of all regulatory proteins
regulatory proteins are key to the activation or repression of -cycle progression, transcription, and apoptosis.
Proteasome inhibitors are currently under investigation as cancer therapeutic agents
Degrade misfolded proteins May contribute to neurodegenerative diseases
Employed in control of the cell division cycle and cell growth
Produce peptides six to nine amino acids in length major histocompatibility complex I peptides to
induces antibodies. Calcium and intracellular signaling
Low concentration maintained Calcium transport pump
Endoplasmic reticulum (ER)=>Cytosol=>plasma membrane Calcium-binding proteins
Activated by high Ca++ concentrations Calmodulin (CALcium MODULated proteIN) (CaM)
Ca++ concentration increases from 0.1 to 0.5 micro molar Binds target proteins
Many not able to bind to Ca++ directly Protein phosphatases
Removal of phosphate group Protein kinase
Attaches phosphate group Ca2+/calmodulin-dependent protein kinases (CaM Kinase)
Involved in many signaling pathways Cyclic nucleotide metabolism (cAMP) Transduction pathways involving phosphorylation Calcium transport (plasma membrane Ca2+ pump) Nitric oxide pathway Regulation of cytoskeletal proteins Apoptosis
Calcium-dependent cysteine proteases Calpain protease
Activates cathepsin Necrosis (Unprogrammed cell death)
Apoptosis (programmed cell death) Elimination of cells no longer necessary (larval tissue) or unwanted (tissue
between the digits) Brain development to remove neurons Defense mechanism
virus-infected cells damaged cells.
balancing cell proliferation Mediated by signaling pathways Major steps involved
Chromatin, nucleus, and cell condense Nucleus is broken apart Blebbing of plasma membrane Fragmentaion into apoptotic bodies Rapid phagocytosis
Mitochondria and lysosomes involvement mitochondrial membrane permeabilized
cytochrome c leaks into the cytosol Lysosomes leak proapoptotic proteins
Cysteine cathepsin
Activation of caspase protease => cell death Caspase (Intrinsic pathway)
Regulated by the Bcl-2 family Ultimate effectors of apoptosis Cysteine residues at their active site
Cleave Aspartic Acid substrate protein. Cell death Receptors (extrinsic pathway)
Receptors that directly induce cell death secrete polypeptides to signal apoptosis
Tumor necrosis factor (TNF) Fas receptor TNF- also mediates other signaling pathways involved in normal α
cellular functions. Cell Differentiation
Derived from a single fertilized ovum Fetal development, cell differentiation
Morphological The way the cell looks (e.g., RBC is round)
Biochemical Differentiation New biochemical components such as proteins (e.g., Hemoglobin in RBC)
Molecular Differentiation: Gene regulation leading to biochemical and morphological changes (e.g.,
transcription of Globin genes in RBC) More differentiated the cell, the less potential to develop into another cell type
Lyon Hypothesis X chromosome inactivation in females
Barr body Female will have same number of X chromosomes as male
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