Western University Biochemistry 3385A Midterm Study Guide

BIOCHEM3385 MIDTERM REVIEW

Topic 1 Lecture 1: Cancer Key Concepts Pt. 1
 Cancer: excessive cell proliferation, tumor forms
 Usually benign but harmful if block organ function/hormone imbalance
 Malignant tumors invade other areas
 Causes of Cancer: lifestyle, genetics, and environment
 Types of Cancer:
 Epithelial Cells – carcinoma, squamous cell carcinoma, adenocarcinoma
 Non-Epithelial Cells (connective tissue, neural cells, hematopoietic tissue) –
sarcoma, glioma/glioblastoma/neuroblastoma, leukemia/lymphoma
 Tumorigenesis – tumor formation
 Cells acquire many mutations (can be somatic/germline, genomic instability)
 Tumors are monoclonal (comes from one cell)
 Allows them to proliferate and escape apoptosis
 Genes Involved in Cancer:
 Oncogenes – normally regulate cell growth/survival (proto-oncogenes), loss of
cell control when hyperactive
 Activation through overexpression, gene amplification, mutation that
keeps product active
 Ex. Ras, Bcl-2
 Tumor Suppressors – prevent over proliferation and induce apoptosis, loss of
cell control when deactivated
 Deactivation through gene mutations (1 allele or 2 alleles), promoter
mutations, epigenetic events (ex. methylation)
 Ex. p53 (transcription factor, also responds to cell cycle arrest, DNA
repair, apoptosis)
 Ex. pRB (transcription factor, also regulates cell cycle)
 6 “Hallmarks of Cancer” -malignant
 Self-sufficient w/o growth signals
 Doesn’t respond to anti-growth signals
 Limitless replication
 Evade apoptosis
 Sustained angiogenesis
 Tissue invasion/metastasis

Topic 1 Lecture 2: Cancer Key Concepts Pt. 2
 Cell growth/proliferation regulated by signalling cascades, starting from extracellular
signals that bind to transmembrane receptors (ex. growth factors), leading to transcription
in nucleus
 The RAS PATHWAY (start of signalling) - oncogene
o Growth factor/signal binds to membrane receptor (upstream stimulatory signal)
o Conformational change, next unit binds
 Either Grb2, or Shc+Grb2
o This contains a GEF called Sos, removes GDP from Ras and allows GTP to bind
= active Ras (can induce the next pathway)

,  The MAPK/ERK PATHWAY (activated by Ras) – kinase phosphorylation cascade
o Ras binds to Raf (kinase)
o Raf activates MEK (phos)
o MEK activates ERK (phos)
o ERK has many targets including nucleus (activates/alters transcription factors)
 IN CANCER: mutation in Ras or Raf to make them hyperactive
 The AKT/PKB PATHWAY (activated by Ras)
o Ras binds to PI3K (kinase), activated
o PI3K phos PIP3 (inositol lipid in membrane), activated
o PIP3 is docking site for AKT/PKB, activated (cell growth, anti-apoptotic)
 PTEN is inhibitor (tumor suppressor), dephos PIP3 so AKT/PKB can’t
bind to it
 IN CANCER: PI3K hyperactivation (either d/t mutation in Ras or PI3K),
PTEN deactivation (mutation – more common)
 The Wnt-B-catenin Pathway (not activated by Ras) – stimulates gene transcription for
cell proliferation
o Complex containing APC, GSK-3B and B-catenin
 Phosphorylates B-catenin, targets it for degradation
 But with Wnt signal from membrane receptor, activates Dishevelled
inhibitor of APC complex
 Complex cannot target B-catenin for degradation
 B-catenin enters nucleus, activates transcription of genes
o FAP (familial adenomatous polyposis) – genetic cancer, many polyps
 Mutation in APC gene, pathway always active w/o needing Wnt signal
 Can also have mutations in p53 and Ras
 The Invasion-Metastasis Cascade:
o Larger tumor = increased risk of metastasis
o Starts with primary tumor formation
 Localized Invasion (out of basal membrane into stroma)
 Intravasation (into blood/lymph)
 Transport
 Arrest in Various Organs (cells may become trapped; if not proceed to
general circulation)
 Extravasation (out from vessels into tissue)
 Colonization (in foreign tissue)
 Familial Breast Cancer (genetic) – case of Shanna Larsen
o Mutations in BRCA1 and BRCA2 (involved in DNA repair)
 Sporadic Breast Cancer
o Types based on histology, stage of cell transformation, tumor size/metastasis,
receptor status (what’s involved – HER2, estrogen/progesterone receptors or triple
negative)
o Prevention: genetic testing, vaccines (HepB, HPV)
o Diagnostic/Treatment: identify tumor markers and involved pathways

Topic 1 Lecture 3: The Cell Cycle

,  Cell Cycle – duplication of cells = 2 identical daughter cells
o 4 stages:
 G1(longest stage) – growth, transcription, etc
 S – synthesis of new DNA
 G2 – growth, transcription, etc.
 M – mitosis + cytokinesis
 Prophase, prometaphase, metaphase, anaphase, telophase,
cytokinesis
o Cycle checkpoints:
 G1/S Checkpoint (most tightly regulated)
 G2/M Checkpoint
 Cell cycle regulated by Cdks (Cyclin-dependent kinases – phosphorylates), bind to
Cyclins
o Levels of Cyclin increase during mitosis (Cdk levels stay constant but need
Cyclin to activate)
 Cyclin D = Cdk 4/6 – G1
 Cyclin A + E = Cdk 2 – G1/S
 Cyclin B = Cdk 1 – G2/M
 Cyclin-Cdk Complex Regulation:
o Phosphorylation (dual – inhibitory + activating; dephos – remove inhibitory)
o Cdk Inhibitors (INK4 = Cyclin D + Cdk4/6, CIP/KIP = ANY complex)
o Degradation of Cyclins (ubiquitination = proteosome degradation)
 The G1/S Transition (most tightly regulated)
o Growth factors/mitogens signal transcription of Cyclin D, forms complex with
Cdk 4/6
o Phosphorylates pRB (tumor suppressor/transcription factor) = released off of E2F
o Transcription of Cyclin A and E genes occurs, cycle proceeds to S phase
 Positive Feedback Loop – Cyclin E/Cdk2 further phosphorylates pRB
 Important to regulate b/c of Restriction (R) Point (committed to S phase,
no longer needs factors/mitogens)
o Regulation of Transition:
 Positive: growth factors/mitogens, inhibit the Cdk inhibitors (INK4 – d/t
TGF-B)
 Negative: withdrawal of factors/mitogens, cellular stress (ex. cell
adhesion)
 The G1/S Checkpoint
o DNA damage signals for activation of p53 (tumor suppressor) by ATM kinase
o p53 activates transcription of CIP (broad Cdk inhibitor)
o CIP inhibits activity of Cyclin A/E + Cdk 2
 The G2/M Checkpoint
o Cyclin B + Cdk 1 working here – increase activity of activating phosphatase
o DNA damage signals for activation of p53 by ATM kinase
 ATM kinase also adds inhibitory phosphate onto activating phosphatase
o P53 activates transcription of CIP (broad)
o CIP inhibits activity of Cyclin B + Cdk 1