The Cell Flashcards
(242 cards)
1
Q
Portion of human genome consisting of protein-encoding genes
A
1.5%
2
Q
Euchromatin
A
Dispersed, transcriptionally active nuclear genetic material.
3
Q
Heterochromatin
A
Densely packed, transcriptionally inactive, nuclear genetic material.
4
Q
Chromosomes
-Number and structure
A
- 46 (23 pairs).
- Visualised during mitosis.
- Consist of paired chromatids connected at centromere and capped with telomeres.
5
Q
Chromatids
A
- String of nucleosomes.
- Short arm (p arm).
- Long arm (q arm).
- Characteristic banding pattern due to relative GC content (less GC content = band, more GC = interband).
6
Q
Telomeres
A
- Repetitive nucleotide sequences.
- Cap ends of chromatids.
- Role: allows for chromosomal replication without deterioration of end genes by sacrificing shortening of itself.
7
Q
Promoter
A
- Non-coding region of DNA.
- Initiates gene transcription.
8
Q
Nucleosome
A
DNA^ wrapped around octameric histone cores.
^~147 DNA base pairs .
9
Q
Enhancer
A
Modulate gene expression by looping back to promoters and recruiting additional factors.
10
Q
Intron
A
Region of pre-mRNA spliced out to form mRNA.
11
Q
Exon
A
Region of mRNA used in translation to encode proteins.
12
Q
Name the Non-coding Gene Regions
A
- Promoter.
- Enhancer.
- Untranslated region (5’ and 3’).
- Short repeats.
- Regulatory factor binding regions.
- Non-coding regulatory RNAs (miRNA, lncRNAs).
- Transposons.
- Telomeres.
- Centromeres.
13
Q
Transposon
A
- Mobile, non-coding genetic element.
- “Jumping genes”- can move around genome during evolution –> variable copy number and gene positioning.
14
Q
SNPs
A
- Single Nucleotide Polymorphisms.
- Variation at a single nucleotide position.
- Almost always bi-allelic.
- Occurs across the genome.
- Has to occur in at least 1% of population.
- 1% in coding regions.
- Predisposition to disease if in noncoding region.
15
Q
“Neutral” SNP
A
SNP with no effect on gene function or individual phenotype.
16
Q
Linkage Disequilibrium
A
“Neutral” SNP, which sits near a disease causing polymorphism, that can be used as a marker for that disease.
17
Q
CNV
A
- Copy Number Variations.
- Multiple nucleotides involved (1 000 - 1 000 000 bp).
- Can be biallelic.
- Formed from duplication, deletion, or complex rearrangements.
- ~50% within coding regions.
18
Q
Histone Octamer
A
- Highly conserved low molecular weight protein which DNA is wrapped around.
- Consist of subunits: 2 x H2A, H2B, H3 and H4.
- Dynamic structures.
- Positively charged.^
- Regulated by nuclear proteins (chromatin remodelling complexes, “chromatin writer” complexes, “chromatin erasers”).
^Allowing compaction of negatively charged DNA.
19
Q
Chromatin Remodelling Complexes
A
Reposition nucleosomes exposing or obscuring gene regulatory elements (e.g. promoters).
20
Q
“Chromatin Writer” Complex
A
- Modify histones through methylation, acetylation, or phosphorylation.
- Modified histones are called “marks”.
- Histone “marks” are reversible.
21
Q
Histone Methylation
A
- Occurs at lysines or arginines.
- Can cause transcription activation or repression.
22
Q
Histone Acetylation
A
- Occurs at lysines.
- Causes opening of chromatin structure allowing for transcription.
- Done by Histone Acetyltransferase (HAT).
- Change reversed by Histone Deacetylase (HDAC).
23
Q
Histone Phosphorylation
A
- Occurs at serines.
- Causes opening or closing of chromatin.
24
Q
“Chromatin Eraser” Complex
A
Reverse histone marks made by “Chromatin Writer” complexes.
e.g HDACs
25
"Chromatin Reader" Complex
Bind histones with particular marks to regulate gene expression.
26
DNA Methylation
* Causes chromatin condensation --> **transcriptional silencing**.
* Regulated by DNA methyltransferases, demethylating enzymes, and methylated DNA binding proteins.
27
What is the role of Chromatin Organising Factors
* Bind non-coding regions.
* Control long range looping of DNA --> regulation of space between enhancers and promoters.
28
Micro-RNA (miRNA)
* Short RNAs (21 - 30 nucleotides).
* **DO NOT** encode proteins.
* Modulate translation of target mRNAs --> **post transcriptional silencing.**
* One miRNA can regulate multiple mRNAs.
29
Formation and action of miRNA
1. **Nucleus:** Transcription of miRNA gene --> primary transcript (pri-miRNA) --> processed to form pre-miRNA^.
2. **Cytoplasm:** Made into smaller segments with help of ***dicer*** enzyme --> mature double-stranded miRNA.
3. Double strand unwinds.
4. Single strand miRNA combines with multiprotein aggregate *RNA-induced silencing complex (RISC).*
5. Attaches to target mRNA --> mRNA cleavage **or** stops translation **--> gene silencing.**
## Footnote
pre-miRNA: single RNA strand with hairpin loop structures forming stretches of dsRNA
30
Small Interfering RNA (siRNA)
* Similar to miRNA.
* Interacts with RISC to cause gene silencing.
* Only has **one** specific mRNA target.
31
What is Long Noncoding RNA (lncRNA)
* Long RNAs (>200 nucleotides)
* **DO NOT** encode proteins.
* Modulates gene expression by multiple mechanisms.
32
Roles of lncRNA
*Promote Gene activation:*
* binds to ribonucleoprotein transcription complex --> facilitates binding to DNA.
*Gene suppression:*
* binds to transcription factors --> inhibits binding to DNA.
*Promote chromatin activation:*
* lncRNA binding can direct acetylation / methylation (or deacetylation / demethylation) --> histone and DNA modification.
*Assembly of protein complexes:*
* act as scaffolds to stabilise secondary / tertiary / multisubunit complexes --> influences chromatin structure / gene activity.
33
E.g. of Gene Suppression by lncRNA
XIST.
* Transcribed from X Chromosome.
* Essential role in X-inactivation in females.
* XIST escapes X-inactivation to "cloak" the X Chromosome from which it came --> gene silencing.
34
Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs) and CRISPR-associated genes (Cas) [e.g. Cas9 nuclease]
* Linked genetic elements.
* Allow bacteria to acquire immunity against phages and plasmids.
35
How Bacteria use CRISPR and Cas9 nuclease to acquire immunity.
* Bacteria take portions of infecting agent DNA.
* **CRISPR** = portion of infecting agent DNA integrated into bacterial genome.
* CRISPR is transcribed and processed to form guide RNA.
* Guide RNA (gRNA) binds **Cas9 nuclease**.
* gRNA-Cas9 nuclease complex binds infecting agent specific site --> cleaving and disabling of infecting agent.
36
Gene Editing
* Use of bacterial CRISPR and Cas9 nuclease principles for editing of human genomes.
37
Performing Gene Editing
* Artificial guide RNAs are designed and introduced into cell.
* Binds to Cas9 --> highly specific cleavage.
* *Non-homologous DNA cleavage:* break repaired by non-homologous end-joining with insertions or deletions --> random disruptive mutations
* *Homologous DNA cleavage:* break repaired by homologous DNA recombination --> introduction of new precise genetic material.
38
Potential applications for Gene Editing
* Repair of inherited genetic diseases.
* Creation of pathogenic mutations in inducible pluripotent stem cells.
* Eliminate less desirable traits.
39
Plasma Membrane Structure
* Phospholipid and cholesterol bilayer with associated proteins and glycoproteins.
* Hydrophilic heads.
* Hydrophobic tails.
* Glycoproteins only found on outside layer and form glycocalyx barrier.
* Mostly fluid structure with areas of 'lipid rafts'.
* Electrical potential difference: inner side negative relative to outer side.
40
'Lipid Rafts'
* Concentrated areas of plasma membrane which are not fluid.
* Usually glycosphingolipids and cholesterol.
41
How Plasma Membrane Proteins associate with the membrane.
* Transmembrane via one or more **hydrophobic alpha-helical amino acid sequences**.
* Insertion into cytosolic side via protein **posttranslation modifications** (addition of prenyl groups or fatty acids).
* Some extracellular proteins link to **glycosylphosphatidylinositol (GPI) tails.**
* Some extracellular proteins **noncovalently associate** with true transmembrane proteins.
42
Roles of Plasma Membrane Proteins
* Ion / metabolite transport.
* Fluid-phase and receptor-mediated uptake of macromolecules.
* Cell-ligand, cell-matrix and cell-cell interactions.
43
Name the three broad types of Membrane Transport
* Passive Diffusion.
* Carriers and Channels.
* Receptor-mediated and Fluid-Phase Uptake.
44
Membrane Transport:
Passive Diffusion
* Small non-polar molecules (e.g. O2 and CO2).
* Larger hydrophobic molecules (e.g. estradiol and Vit D).
* **At low rates:** Small polar molecules (<18 Da e.g. water).
45
Membrane Transport:
Carriers and Channels
*Channel Proteins:*
* Used when concentration gradient can drive movement i.e. *passive.*
* Create hydrophilic pores.
* When open -> **rapid** movement.
* Solutes restricted by size and charge.
*Carrier Proteins:*
* Used when moving against concentration gradient. Requires energy i.e. *Active.*
* Bind specific solute.
* Undergo changes -> **slow** transfer.
46
Membrane Transport:
Receptor-mediated and Fluid Phase uptake
*-What is it and what are the types*
Endocytosis of fluids and macromolecules.
Involves membrane bound vesicles.
Types:
* Caveolae-mediated endocytosis.
* Receptor-mediated endocytosis.
* Phagocytosis.
* Transcytosis.
47
Membrane Transport:
Receptor-mediated and Fluid Phase uptake
*Caveolae-mediated Endocytosis*
Caveolae (little caves):
* Non-coated plasma membrane invaginations.
* Associated with GPI-linkage molecules, cAMP binding proteins, src-family kinases, and folate receptor.
* Caveolin = major structural protein.
Process:
1. *Potocytosis ('cellular sipping')* of caveolae with bound molecule and extracellular fluid.
2. Formation of vesicle.
3. Fusion with endosomes.
4. Caveolae degraded or recycled back to membrane.
48
Membrane Transport:
Receptor-mediated and Fluid Phase uptake
*Receptor-mediated Endocytosis*
1. Membrane receptor binds to macromolecule (e.g. transferrin, LDL receptor).
2. Taken into cell at *clathrin-coated pits.*
3. Clathrin proteins spontaneously assemble into a basket-like lattice which drives endocytosis of receptor, macromolecule and extracellular fluid (*fluid-phase pinocytosis)*.
4. Formation of clathrin-coated vesicle.
5. Clathrin coating rapidly lost.
6. Fusion with *early endosome (acidic intracellular structure).*
7. Release of macromolecules from receptors from low pH. **Some receptors released** from endosome and returned to plasma membrane by exocytosis (e.g transferrin).
8. Progressive maturation of endosome (late endosome).
9. Fusion with lysosome.
10. If receptor remains -> **receptor degradation** (e.g. epidermal growth factor receptor).
49
Membrane Transport:
Receptor-mediated and Fluid Phase uptake
*Phagocytosis*
*Cellular eating.*
Restricted to specialised cells (phagocytes e.g. macrophages, neutrophils).
Process:
1. Membrane invagination to engulf large particles (e.g. microbes, dead cell fragments).
2. Formation of phagosome (vesicle with particle).
3. Fusion with lysosome (phagolysosome).
4. Degradation of internalised material.
50
Membrane Transport:
Receptor-mediated and Fluid Phase uptake
*Transcytosis*
* **Transcellular** transport of endocytosed intact proteins (e.g. ingested abs in maternal milk) or large solute volumes.
* Either apical-to-basal or basal-to-apical directions.
51
What is the Cytoskeleton and what are the major components.
Dynamic network of structural proteins.
3 major proteins:
* Actin microfilaments.
* Intermediate filaments.
* Microtubules.
52
Cytoskeleton:
Actin microfilaments:
*-Structure and Roles*
**Structure:**
* 5 - 9 nm diameter.
* Structure: 2 x strands of actin proteins twisted together.
* Chains form networks with regulatory proteins (motor proteins).
* Can actively re-organise.
**Roles:**
* Control cell shape / movement - Muscle contraction, with help of mysoin.
* Cell migration - form neutrophil pseudopodia used in diapedesis.
* Cell division during mitosis.
* Vesicular transport.
* Epithelial barrier.
53
Cytoskeleton:
Intermediate filaments:
*-Structure and Roles*
**Structure:**
* 10nm diameter.
* Comprised of many types of proteins depending on cell type e.g. keratin proteins and nuclear lamins.
* Form **ropelike polymers** providing tensile strength.
* Chrctrstc tissue-specific expression patterns (USE: can be useful to assign a cell of origin e.g. in poorly dfferentiatied tumours).
**Roles:**
* Structural strength of cell.
* Anchor cells to each other via desmosomes.
* Anchor cell to extracellular matrix via hemidesmosomes.
* Anchor organelles in cells.
Examples:
* Vimentin (mesenchymal cells - fibroblasts, endothelium).
* Desmin (muscle cells).
* Glial fibrillary acidic protein.
* Cytokeratins.
* Lamins (nuclear lamina).
54
Cytoskeleton:
Microtubules:
*-Structure and Roles*
* 25nm diameter.
* Hollow tubes of alpha and beta-tubulin dimers.
* Dynamic structure.
* Polarised - negative end anchored in microtubule organising centre, positive end elongates / recedes.
Roles:
* "Railroads" for intracellular transport.
* Resists compression force -> maintaining cell shape.
* Form centrioles which separates chromatid pairs during mitosis.
* Core of primary (non-motile) cilia (e.g. photoreceptors).
* Core of motile cilia (e.g. bronchial epithelium, fallopian epithelium).
* Core of flagella (sperm).
55
Cytoskeleton Roles
* Determines cell shape.
* Anchors organelles and the cell.
* Determines cell polarity.
* Moves intracellular organelles.
* Allows cell movement.
56
Cell-Cell Interactions:
*How*
Occur via junctions.
3 types:
* Occluding junctions (tight junctions).
* Anchoring junctions (adherens junctions, desmosomes and hemidesmosomes).
* Communicating junctions (gap junctions).
57
Cell-Cell Interactions:
*Occluding Junctions*
* AKA tight junctions.
* Seals adjacent epithelial cells together.
* Selectively permeable - Restricts paracellular movement of ions and molecules.
* Assists in maintenance of cellular polarity.
* Dynamic and can be modified to facilitate healing and inflammatory cell migration.
* Proteins involved: claudin, tight junction-associated MARVEL protein (TAMP) family, zonula occludens protein family, cingulin.
58
Cell-Cell Interactions:
*Communicating Junctions*
* AKA gap junctions.
* "Pore" (connexons) between cells.
* Permit diffusion of ions, nucleotides, sugars, AAs, vitamins and other small molecules.
* Protein = connexin.
* Low intracellular pH or high intracellular calcium --> reduced permeability of junction.
59
Cell-Cell Interactions:
*Anchoring Junctions*
Mechanically attach cells to other cells or the extracellular matrix (ECM)
Adherins junctions:
* Glycoprotein = cadherins.
* Linked to actin microfilaments --> influences cell shape +/- motility.
Desmosomes:
* Found between cells (usually more basal).
* Glycoprotein = cadherins.
* Linked to intermediate filaments.
Hemidesmosomes (Half desmosomes):
* Found between cell and ECM / basement membrane.
* Protein = integrins.
* Linked to intermediate filaments.
60
Sirtuin Activity
* Ultimately **increases longevity**.
Acts on:
*Adipose tissue:*
* Increase lipolysis.
* Increase insulin sensitivity.
* Decrease lipid profile.
*Metabolism:*
* Increases insulin secretion.
* Increases fat metabolism.
* Decreases lipid profile.
*Cancer cells:*
* Increases tumour suppression.
* Increases genome stability.
* Decreases transcriptional activity of p53.
*Cell aging:*
* Telomerase stability.
Also:
* Acts on histone acetylation and deacetylation.
* May promote transcription of genes encoding for proteins --> increased metabolic activity and inhibition of free radicals effects.
## Footnote
NB. Red wines increase sirtuins.
61
A study of peripheral blood smears shows neutrophil nuclei of women have a Barr body, an inactivated X chromosome.
Which RNA most likely plays a role in Barr body formation?
lncRNA
62
A nuclear chromosomal gel is found to be actively transcribing mRNA that is transported into the cell cytoplasm. No observed protein product is formed from translation of this mRNA.
How is silencing of this active gene's mRNA most likely to occur?
Binding to miRNA.
63
A part of red wine is credited for longevity when calorie restriction is also used.
Which intracellular substance will most likely mediate the effect of calorie restriction upon increased longevity?
Sirtuins.
64
40 yo F with chronic congestive heart failure. 2 month history of productive cough with rust-coloured sputum. Sputum cytology shows numerous haemosiderin-laden macrophages.
Which subcellular structures in macrophages is most important for accummulation of this pigment?
Lysosome.
65
Cells subject to high levels of UV radiation show cellular damage in the form of increased cytosolic aggregates of denatured proteins on electron microscopy. These protein aggregates are also found in proteasomes.
Which substance most likely binds to the denatured proteins, targeting them for catabolism by cytosolic proteasomes?
Ubiquitin.
66
Ubiquitin
Targets denatured proteins and facilitates their binding to proteasomes --> protein breakdown to peptides.
67
At a surgical incision site, endothelial cells produce vascular endothelial growth factor which cause sprouting and migration of endothelial cells into the wound to establish new capillaries.
Which intracellular proteins is most important in facilitating movement of endothelial cells?
Actin.
68
Release of epidermal growth factor into an area of denuded skin causes mitogenic stimulation of the skin epithelial cells.
Which protein is most likely involved in transducing the mitogenic signal from the epidermal cell membrane to the nucleus?
RAS proteins.
69
RAS proteins
Transduce signals from growth factor receptors (e.g. epidermal growth factor) that have intrinsic tyrosine kinase activity.
70
Various soluble mediators are added to a cell culture containing epidermal cells to determine which of the mediators may be useful for promoting epidermal cell growth. When epidermal growth factor is added, it binds to epidermal cell surgace receptors, with subsequent transcription factor translocation and DNA transcription.
This effect is most likely to be mediated through which intracellular pathways?
Mitogen-activated protein (MAP) kinase.
71
Mitogen-activated protein (MAP) kinase cascade
* Involved in signalling from activation via cell surface receptors for growth factors.
* Particularly important for signalling of EGF and fibroblast growth factor.
72
Which factor is most likely effective in promoting angiogenesis for skin healing in skin ulcerations.
Basic Fibroblast growth factor.
73
Basic Fibroblast Growth Factor
Potent inducer of angiogenesis, participating in all steps.
74
Which step in the inflammatory-repair response is most likely affected by neutralisation of transforming growth factor beta?
Production of collagen.
75
Transforming Growth Factor beta Roles
* Stimulates many steps in fibrgenesis (e.g. fibroblast chemotaxis, production of collagen by fibroblasts).
* Inhibits degradation of collagen.
76
Example of Pathogenic genome variations
Germline mutation of BRCA1 gene.
77
BRCA1 gene location
17q21
| Chromosome 17
78
BRCA1 protein roles
* DNA repair.
* Cell cycle regulation.
* Regulation of apoptosis.
79
BRCA1 mutations
* Hereditary Breast cancer.
* **Autosomal dominant.**
* x 5 risk of breast ca by 70.
* Prevalanece 1/500 - 1/800.
* Ashkenazi Jewish decent people >1/100 prevalence, mutation 185delAG and 5382insC.
80
What are Epigenetics?
Heritable changes in gene expression that are not caused by alterations in DNA sequence.
81
Cell Cycle
1. G0.
2. G1
3. G1 / S CHECK POINT.
4. S.
5. G2.
6. G2 / M CHECK POINT.
7. M.
82
What regulates cell proliferation in the cell cycle?
* Cyclins.
* Cyclin-dependent kinases (CDKs).
83
Which cyclin / CDK detection guides diagnosis of osteo- and liposarcomas and at which part of the cell cycle is this found?
MDM2 - CDK4 co-expression at G1-S checkpoint.
84
What are the cyclins / CDKs that regulate G1 --> G1 / S Checkpoint by phosphorylating the Rb protein^?
## Footnote
^Rb --> pRB
* Cyclin D / CDK4.
* Cyclin D / CDK6.
* Cyclin E / CDK2.
85
What are the Three families of Extracellular matrix proteins?
1. Water-hydrated gels (e.g. proteoglycans and hyaluronan).
2. Adhesive glycoproteins (e.g. laminins, fibronectin).
3. Fibrous structural proteins (e.g. collagen, elastin).
86
If a researcher wished to identify early signs of epithelial cell invasiveness in a low stage colon carcinoma, which cell adhesion alteration would be MOST useful to detect?
Decreased cadherin expression.
## Footnote
Cadherin = part of adherin junctions and desmosomes i.e. **form part of anchoring junctions**.
Steps in invasion:
1. Loosening of anchoring junctions.
2. Degradation of ECM with loss and cleavage of type IV collagen and plasminogen activation.
3. Migration and invasion.
87
Cell signalling:
Growth Factor Downstream Signalling:
*-RAS / MAPK pathway*
1. Growth factor binds to **tyrosine kinase-based growth factor receptor.**
2. Receptor dimerisation and autophosphorylation of tyrosine residues in inner cell.
3. Binding of adaptor proteins.
4. Coupling to inactive RAS.
5. Activation of RAS.
6. Activates P13K --> Akt --> mTOR AND RAF --> MAPK.
7. Activation of transcription.
8. Production of MYC protein.
9. Cell cycle progression.
## Footnote
Therefore, mutation in RAS --> affect cell proliferation.
88
What would you use to study the integrity of the basement membrane?
Laminin.
89
Examples of Copy Number Variations (CNVs)
* Oncogene duplications in cancer.
* Trinucleotide (CAG) repeats in Huntington's disease.
90
Histone H1
* Linker molecule.
* Sits on linker DNA between nucleosomes.
* Stabilises overall chromatin architecture.
91
In cancer, what therapeutic targets can be used to reverse epigenetic alterations?
* HDAC (chromatin erasers) inhibitors against HDAC.
* DNA methylation inhibitors against DNA methylation.
92
Which molecular technique would you most likely use to identify germline mutations of genes such as BRCA1 in a female individual of Ashkenazi Jewish descent?
Targeted DNA sequencing of BRCA1 gene in blood sample.
## Footnote
Targeted for 185delAG and 5382insC
93
Which molecular technique would you most likely use to identify germline mutations of genes such as BRCA1 in a female individual from the general population?
Next-Gen sequencing.
94
Which family of CDK inhibitors can affect all CDK molecules?
* p21.
* p27.
* p57.
95
What is the consequence of persistent P16 or p16 INK4A (CDKN2A gene)?
* Inhibition of CDK4 (and subsequently CDK6).
* Inability to move from G1 --> S.
* Rb remains unphosphorylated.
96
How can detection of P16 be used clinically?
Detection / evaluation of lesions with inactivation of pRB:
* HPV infection.
* Anogenital lesions.
* Rb gene alteration (e.g. gastric and pulmonary adenocarcinoma).
97
What are the core properties of stem cells?
* Long-term self-renewal ability.
* Differentiation potential.
98
Stem Cell Types:
Totipotent stem cells:
*-Where found?*
Zygotes.
99
Stem Cell Types:
Totipotent stem cells:
*-Differentitates to?*
* Any cell type of the body (three germ layers).
* Placenta.
100
Stem Cell Types:
Pluripotent (embryonic) stem cells:
*-Differentiates to?
Any cell type in the body.
101
Stem Cell Types:
Multipotent and lineage committed cells:
*-Differentiates to?*
## Footnote
i.e. Organ-specific stem cells
Gives rise to a limited number of differentiated cell types.
102
Roles of Extracellular Matrix
* Mechanical support.
* Regulation of cell proliferation.
* Scaffolding for tissue renewal.
* Foundation for establishment of tissue microenvironments.
103
Roles of Extracellular Matrix:
*-Mechanical Support*
Provides:
* Cell anchorage.
* Cell migration.
* Maintenance of cell polarity.
104
What does disruption to the extracellular matrix cause in regards to mechanical support of the cell?
Allows for invasiveness in the context of solid tumours.
105
Roles of Extracellular Matrix:
Regulator of cell proliferation:
*-How?*
By:
* Binding and displaying growth factors.
* Signaling via cellular integrin family receptors (e.g. reserves Growth Factor during injury / inflammation).
106
Roles of Extracellular Matrix:
Scaffolding for tissue renewal:
*-Importance?*
Basement membrane integrity and the stromal scaffold is critical for organised tissue regeneration.
107
Roles of Extracellular Matrix:
Foundation for establishment of tissue microenvironments:
*-Importance?*
* Separates epithelial / endothelial cells from connective tissues.
* Functional role in renal filtration apparatus.
* Functional role in the blood-brain barrier.
108
Extracellular matrix proteins:
Water-hydrated gels:
*-Role*
* Compressive resistance.
* Lubrication.
109
Extracellular matrix proteins:
Adhesive glycoproteins:
*-Role*
Connect Extracellular matrix elements to one another and to cells.
110
Extracellular matrix proteins:
Fibrous structural proteins:
*-Role*
* Tensile strength.
* Recoil.
111
Extracellular matrix proteins:
Fibrous structural proteins:
*-Types*
* Fibrillar collagens (e.g. Types I, II, III and V).
* Nonfibrillar collagens (e.g. Type VII collagen).
112
Extracellular matrix proteins:
Fibrous structural proteins:
*-Fibrillar collagens location*
Linear fibrils in:
* Bone.
* Tendon.
* Cartilage.
* Blood vessels.
* Skin.
* Healing wounds and scars (enriched in these areas).
113
Extracellular matrix proteins:
Fibrous structural proteins:
*-Fibrillar collagens structure*
* Triple helices crosslinked via covalent bonds.
* Formed by vitamin-C dependent lysyl hydroxylase.
114
What can ascorbate deficiency cause in children and why?
**What:**
Skeletal deformities.
**Why:**
Vitamin C is required for formation of fibrillar collagens found in bones, tendons and cartilage.
115
What can collagen or lysyl hydroxylase mutations cause and why?
**What:**
Osteogenesis imperfecta.
**Why:**
Lysyl hydroxylase is required for formation of fibrillar collagen. No lysyl hydroxylase --> no collagen --> abnormal bones, tendons, cartilage, blood vessels, and skin.
116
Extracellular matrix proteins:
Nonfibrillar collagens:
*-Role*
* Contributes to basement membranes.
* Helps regulate collagen fibril diameters.
* Maintains structure of squamous epithelium.
117
What do mutations in Type VII (nonfibrillar) collagen cause?
Blistering skin disease.
118
What does loss of E-cadherin cause?
Disruption of adherens junctions --> discohesive invasion pattern of some gastric cancers and lobular breast carcinomas.
119
What is an example of RAS gene mutations and what do they cause?
Mutations:
* KRAS (Found in >50 % colorectal cancer and >80% polyductyl adenocarcinoma (PDAC)).
Cause:
* Constitutive activation of RAS-MAPK.
## Footnote
**NB.** Cannot give anti-EGFR mAb to prevent RAS / MAPK pathway because pathway already activated by mutation
120
What are the types of Growth Factors (GF)?
* Epidermal GF (EGF).
* Hepatocyte GF (HGF / Scatter factor).
* Vascular endothelial GF (VEGF).
* Transforming GF-beta (TGH-beta).
* Transforming GF-alpha.
* Platelet-derived GF (PDGF).
* Fibrinoblast GF (including acidic [FGF-1] and basic [FGF-2]).
* Keratinocyte GF (KGF) e.g. FGF-7.
121
Epidermal growth Factor
*-Sources*
* Activated macrophages.
* Salivary glands.
* Keratinocytes.
* Others.
122
Epidermal GF:
*-Roles*
* Mitogenic for many cell types.
* Stimulates epithelial cell migration.
* Stimulates formation of granulation tissue.
123
Hepatocyte GF:
*-Sources*
* Fibroblasts.
* Stromal cells in the liver.
* Endothelial cells.
124
Hepatocyte GF:
*-Roles*
* Enhances proliferation of hepatocytes and other epithelial cells.
* Increases cell motility.
125
Vascular Endothelial GF:
*-Sources*
Mesenchymal cells.
126
Vascular endothelial GF:
*-Roles*
* Stimulates proliferation of endothelial cells.
* Increases vascular permeability.
127
Transforming GF-beta:
*-Sources*
* Platelets.
* T lymphocytes.
* Macrophages.
* Endothelial cells.
* Epithelial cells.
* Smooth muscle cells.
* Fibroblasts.
128
Transforming GF-beta:
*-Roles*
* Chemotactic for leukocytes and fibroblasts.
* Stimulates ECM protein synthesis.
* Suppresses acute inflammation.
129
Platelet-derived GF:
*-Sources*
* Platelets.
* Macrophages.
* Endothelial cells.
* Smooth muscle cells.
* Keratinocytes.
130
Platelet-derived GF:
*-Functions*
* Chemotactic for neutrophils, macrophages, fibroblasts and smooth muscle cells.
* Activates and stimulates proliferation of fibroblasts, endothelial cells and other cells.
* Stimulates ECM protein synthesis.
131
What are Cell Surface Receptors
Transmembrane proteins with extracellular domains that bind active ligands.
132
What can ligand binding to cell surface receptors initiate?
1. Open ion channels, typically at the synapse between electrically excitable cells.
2. Activate an associated GTP-binding regulatory protein (G protein).
3. Activate an endogenous OR associated enzyme (often tyrosine kinase).
4. Trigger a proteolytic event OR change protein binding / stability to activate a latent transcription factor.
133
Plasma Membrane Phospholipid:
Phosphatidylinositol:
*-Where found*
Both outer and inner membrane.
134
Plasma Membrane Phospholipid:
Phosphatidylinositol:
*-Inner membrane Functions*
* Phosphorylated --> scaffold for intracellular proteins.
* Hydrolysed by phospholipase C --> intracellular DAG and IP3 signalling.
135
Plasma Membrane Phospholipid:
Phosphatidylserine:
*-Where found*
Mostly inner membrane.
136
Plasma Membrane Phospholipid:
Phosphatidylserine:
*-Functions*
* Electrostatic protein interactions.
* Platelet phosphatidylserine = cofactor in blood clotting.
* When flipped to outer membrane = potent "eat me" signal during apoptosis.
137
Plasma Membrane Phospholipid:
Gycolipids and Sphingomyelin:
*-Where found*
Outer plasma membrane.
138
Plasma Membrane Phospholipid:
Gycolipids and Sphingomyelin:
*-Function*
* Involved with charge-based interactions.
* E.g. inflammatory cell recruitment and sperm-egg fusion.
139
Endoplasmic Reticulum:
Rough ER:
*-Function*
Synthesis of secreted proteins AND transmembrane proteins / lipids.
For:
* Plasma membrane.
* Intracellular organelles.
140
Endoplasmic Reticulum:
Rough ER:
*-Example of protein folding failure*
CFTR protein in cystic fibrosis.
1. Codon deletion --> single AA (Phe508) absent.
2. Protein misfolding.
3. rER retention of misfolded protein.
4. Catabolism of misfolded protein.
5. Reduced surface expression of CFTR protein.
141
Endoplasmic Reticulum:
Rough ER:
*-Events of excess misfolded protein*
1. Excess accumulation of misfolded protein.
2. Exceeds rER capacity for degradation.
3. *ER stress response* (AKA *unfolded protein response*).
4. Overall reduction in protein synthesis AND increase in chaperone proteins (to assist with protein refolding).
5. Apoptosis if overload unable to be corrected.
142
Golgi Apparatus:
*-Function*
Progressively modify proteins from *cis* (end near ER) to *trans* (end near plasma membrane).
143
Endoplasmic Reticulum:
Smooth ER:
*-Function*
* Assists in transport of newly synthesised proteins from rER to Golgi apparatus.
* Metabolise compounds e.g. phenobarbitol.^
* Sequesters intracellular calcium for:
- apoptosis.
- muscle contraction / relaxation in muscle cells (sER = sarcoplasmic reticulum).
## Footnote
^Found in large numbers in cells which catabolise these compounds e.g. hepatocytes.
**NB.** Phenobarbitol catabolised by cytochrome P450
144
Proteasome:
*-Function*
Degrade cytosolic proteins including denatured or misfolded proteins.
145
Proteasome:
*-Degradation process*
1. Cytosolic protein tagged by multiple **ubiquitin** molecules through activity of E1, E2 and E3 ubiquitin ligases.
2. Polyubiquitinated molecules unfolded and funneled into polymeric proteasome complex.
3. Degradation of protein into small (6 - 12 AA) fragments.
146
Polymeric proteasome Complex
* Cylindrical multi-subunit complex.
* Active sites of multiple proteases pointed at complexes hollow core.
147
Cell Cycle:
*-What occurs in G1 Phase*
* Growth in mass.
* Centrosome duplication.
* Restriction point - stage whereby cell is committed to advance further into the cell cycle without requiring any more growth signal.
## Footnote
Enter G1 from G0 or M phase.
148
Cell Cycle:
*-What occurs at G1-S Check Point*
* Check for DNA damage.
* Rb is phosphorylated to pRB.
149
Cell Cycle:
*- What occurs in S Phase*
Chromosome duplication.
150
Cell Cycle:
*-What occurs in G2 Phase*
151
Cell Cycle:
*-What occurs at G2-M Check Point*
* Check for damaged or unduplicated DNA.
152
Cell Cycle:
*-What occurs in M Phase*
* Mitosis (Prophase, Metaphase, Anaphase, Teleophase).
* Cell division.
153
Gene involved in Familial adenomatous polyposis?
Adenomatous polyposis coli (APC).^
## Footnote
Tumour suppressor gene, can lead to colorectal cancer if colon not resected.
154
Mitochondria half life
1 - 10 days.
155
Mitochondria Functions
* Energy generation from glucose and fatty acids.
* Intermediate metabolism.
* Cell death (necrosis and apoptosis).
156
Mitochondrial Structure
* Core matrix space: contains enzymes for glycolytic and trycarboxylic acid cycles.
* Inner mitochondrial membrane: contains enzymes of the respiratory chain folded into cristae.
* Intermembrane space: site of nucleotide phosphorylation.
* Outer membrane: contain porin proteins which form voltage-dependent anion channels permeable to small molecules.
157
What is thermogenin (AKA uncoupling protein-1 [UCP-1]) and what is it's role?
* Mitochondrial inner membrane protein.
* Enriched in brown fat.
**Role:**
* Hydrogen ion transporter --> stops protein gradient (part of oxidative metabolism for ATP generation) --> rapid substrate oxidation without ATP synthesis --> heat generation of tissues and release of **reactive oxygen species.**
158
Mitochondrial Function:
*-Energy Generation*
* Oxidative phosphorylation.
* Generation of 36 - 38 ATP, Co2 and H2O per glucose molecule.
* Process which **supports cellular energy maintenance.**
159
Mitochondrial Function:
*-Intermediate Metabolism*
* Ensures adequate building blocks for growth by increasing uptake of glucose and glutamine and switching to aerobic glycolysis.^
* Each glucose molecule --> lactic acid + 2 ATP + intermediates (which can form lipids, AA, proteins and nucleic acid).
* Process which **supports cellular proliferation.**
## Footnote
^Counter-intuitive phenomenon known as *Warburg effect.*
160
Mitochondrial Function:
Cell death:
*-Necrosis*
1. External cellular injury (toxin, ischaemia, trauma).
2. Mitochondrial damage.
3. Mitochondrial permeability transition pores in outer membrane.
4. Release of hydrogen from mitochondria into cell.
5. Dissipation of proton gradient.
6. Mitochondria unable to produce ATP.
7. Cell death.
161
Mitochondrial Function:
Cell Death:
*-Apoptosis*
1. Extrinsic (cytotoxic T cells or inflammatory cytokines) or Intrinsic (DNA damage or intracellular stress) signals.
2. Formation of oligomerised Bax and Bak protein pores.
3. Mitrochondrial outer membrane permeabilisation (MOMP).
4. Release of cytochrome C.
5. Caspase activation.
6. Apoptosis.
162
In Mitochondria, what can a failure of normal pro-apoptotic signalling OR too much anti-apoptotic signalling cause?
Malignancy.
163
In Mitochondria, what can excess pro-apoptotic signalling OR lack of anti-apoptotic signalling cause?
Premature cell death as seen in neurodegenerative disorders.
164
What cell signalling are G protein-coupled receptors and tyrosine kinase-associated recepors typically involved in?
Signalling which **drives cellular proliferation.**
165
What are the three main classes of transmembrane receptors?
* G coupled protein receptors.
* Enzyme coupled receptors.
* Ion Channel receptors.
166
What are G-protein coupled receptors?
Seven-pass transmembrane receptor (receptor binding site outside cell, then receptor passes into and out of cell membrane seven times, ending inside cell).
167
What do G-protein coupled receptors activate inside a cell?
Guanine nucleotide-binding proteins (G-proteins).
168
What subunits make up G-proteins?
* Alpha.
* Beta.
* Gamma.
169
Which subunits of the G-protein are anchored to the cell membrane to keep the protein next to the receptor?
* Alpha.
* Beta.
170
What happens to active G-proteins.
**Inactive state:**
No ligand binding to G-protein coupled receptor = G-protein bound to Guanosine Diphosphate (GDP).
**Active state:**
1. Ligand binds to G-protein coupled receptor.
2. Receptor changes shape.
3. G-protein releases GDP and binds GTP (Active state).
4. Alpha subunit separates from beta and gamma.
5. Interaction with other proteins (either stimulating or inhibiting).
6. Interaction requires phosphate --> GTP becomes GDP again.
7. Alpha subunit re-binds to other subunits on receptor.
171
What are the three types of G-proteins
* Gq
* Gi
* Gs
172
What is the pathway triggered by Gq protein
1. Activates **phospholipase C** enzyme (found in cell membrane).
2. Cleavage of phosphatidylinositol 4,5-bisphosphate (phospholipid) into inositol triphosphate (IP3) and diacylglycerol (DAC).
3. a) IP3 opens calcium channels in endoplasmic reticulum. b) DAC binds protein kinase C.
4. **Leakage of calcium** into cytoplasm from ER.
5. Increasing cytoplasm electrical charge and activation of protein kinase C
6. Cell depolarisation and activation of other proteins by active protein kinase C.
173
What is the pathway triggered by Gs protein
1. Stimulation of adenylate cyclase enzyme.
2. Transforms ATP into cyclic adenosine monophosphate (cAMP) by removing 2 phosphates from ATP.
3. cAMP binds protein kinase A^ regulatory subunit.
4. Dissociation of protein kinase A subunits.
5. Catalytic subunit free to phosphorylate other proteins to trigger a cellular response.
## Footnote
^Made up of 2 subunits: regulatory subunit and catalytic subunit.
174
What is the pathway triggered by Gi protein
1. Inhibits adenylate cyclase.
2. Negative feedback on protein Gs.
3. Helps inactivate cells.
175
What are enzyme-coupled receptors?
Single-pass transmembrane proteins with 2 parts:
1. Receptor
2. Enzyme
176
What is the main action of the enzymatic domain of an enzyme coupled receptor?
Phosphorylation of receptor domain.
## Footnote
**NB.** Enzyme is usually a protein kinase.
177
What are the three main types of enzyme-couple receptors and what are they based on?
* Receptor tyrosine kinase.
* Tyrosine kinase associated receptors.
* Receptor serine / threonine kinase.
**Based on:**
Amino acid at which receptor is phosphorylated.
178
How do Ion Channel Receptors work?
* No bound ligand = channel closed.
* Specific ligand binding = opening of channel --> passive flow of ions (Cl-, Ca2+, Na+, K+) down gradient into cell --> shift in electrical charge in cell --> triggers cellular response.
179
What are transmembrane protein receptors for?
Hydrophilic (water-loving) ligands which cannot cross cell membrane into cell.
180
Cell Cycle:
*-What occurs in G0 Phase*
* Rest phase.
* Quiescent cells not actively cycling.
181
What happens to replicating cells which fail check point checks?
* Cell cycle progression arrests.
* DNA repair mechanisms triggered.
If unable to repair:
* Apoptosis triggered, OR
* Cell enters senescence (non-replicative state) through p53-dependent mechanisms.
182
What molecules regulate cell cycle check points?
Cyclin-dependant kinase (CDK) inhibitors.
183
Which family of CDK inhibitors regulate cyclin D / CDK4 and cyclin D / CDK6 and which part of the cycle do they act?
INK4 inhibitors:
* p15.
* p16.
* p18.
* p19.
Act at G1 - S Checkpoint.
184
Which cells can cycle continuously through cell cycle?
Labile tissues e.g. epidermis and GI tract.
185
Which cells are generally quiescent but can enter cell cycle?
Stable cells e.g. hepatocytes.
186
Which cells may lose the ability to enter the cell cycle and proliferate?
Permanent cells e.g. neurons and cardiac myocytes.
187
What are the cyclins / CDKs that regulate S Phase?
* Cyclin A / CDK2.
* Cyclin A / CDK1.
188
What are the cyclins / CDKs that regulate G2 - M Checkpoint?
Cyclin B / CDK1.
189
G-protein coupled receptors common signalling pathway results in?
Release of calcium from ER.
190
What are nuclear receptors?
Hormone receptors found within a cell NOT on the cell membrane.
191
How do nuclear receptors work?
1. Lipid soluble ligands diffuse through membrane into cell.
2. Bind to nuclear receptors.
3. Receptor-ligand complex fprmed.
4. Complex directly binds DNA.
5. Activation or repression of gene transcription.
192
What are *Notch* receptors?
* Cell membrane receptors.
* Rely on protein - protein interactions to transduce signals.
193
How do *Notch* receptors work?
1. Ligand bind *Notch* receptor.
2. Triggers cleavage of *Notch.*
3. Intracellular *Notch* (IC Notch) fragment produced.
4. IC Notch enters nucleus.
5. Triggers transcription of target DNA.
194
What are Frizzled Receptors.
* Distinct set of G-protein coupled transmembrane receptors.
* Use protein-protein interactions to transduce signals.
195
How do Frizzled receptors work?
1. Wnt protein ligand binds Frizzled receptor.
2. Activation of *Dishevelled* protein.
3. Disruption of beta-catanin multi-subunit degradation complex^ AND release of intracellular beta-catanin.
4. Migration to nucleus.
5. Activates transcription.
## Footnote
^Complex which normally degrades beta-catanin unless this pathway is triggered.
196
What are two common transcription factor genes which regulate cell division?
* MYC.
* JUN.
197
What is the most common cell cycle inhibiting gene?
TP53.
198
What is interstitial matrix?
* Part of Extracellular matrix.
* 3D, amorphous, semi-fluid gel.
199
What synthesises interstitial fluid?
Mesenchymal cells.
200
What are the major non-fluid constituents of interstitial matrix?
* Fibrillar collagen.
* Non-fibrillar collagen.
* Fibronectin.
* Elastin.
* Proteoglycans.
* Hyaluronate.
201
What are basement membranes?
* Component of extracellular matrix within connective tissues.
* Flat lamellar mesh between epithelium and mesenchymal cells.
202
What is the purpose of basement membranes?
Specialised surface for cell growth.
203
What are the main components of basement membranes?
* Non-fibrillar type IV collagen.
* Laminin.
* Proteoglycan.
204
What synthesises basement membrane components?
* Overlying epithelium.
* Underlying mesenchymal cells.
205
How do epithelial cells and mesenchymal cell (e.g. fibroblasts) interact with the extracelllular matrix?
Via integrins.
206
What are the three families of extracellular matrix components?
1. Fibrous structural proteins.
2. Water-hydrated gels.
3. Adhesive glycoproteins.
207
ECM components:
Fibrous structural proteins:
*-Role*
* Tensile strength (collagens).
* Recoil (elastin).
208
ECM components:
Fibrous structural proteins:
*-Main examples*
* Collagens.
* Elastins.
209
ECM components:
Fibrous structural proteins:
*-Collagen structure*
Three separate polypeptide chains braided into a ropelike triple helix.
210
ECM components:
Fibrous structural proteins:
*-Examples of Fibrillar collagens*
Collagen types:
* I
* II
* III
* V
211
ECM components:
Fibrous structural proteins:
*-Fibrillar collagen structure*
* Linear fibrils stabilised by interchain H bonds.
* Triple helices bound via lateral cross-linking of covalent bonds.
212
ECM components:
Fibrous structural proteins:
*-Fibrillar collagen locations*
Connective tissue in:
* Bone.
* Tendons.
* Cartilage.
* Blood vessels.
* Skin.
* Healing wounds and scars.
213
ECM components:
Fibrous structural proteins:
*-What forms covalent bonds in fibrillar collagens?*
Lysine hydroxylation by lysyl hydroxylase.
214
What is lysyl hydroxylase dependent on?
Vitamin C.
215
Why do children with ascorbate (Vitamin C) deficiency have skeletal deformities?
* Vitamin C required for lysyl hydroxylase to form covalent bonds between fibrillar collagens.
* No covalent bonds = no tensile strength of fibrillar collagens.
* Fibrillar collagens responsible for forming connective tissue in bones, tendons, cartilage.
* No strength of fibrillar collagens = no strength of connective tissue in bones, tendons, cartilage = skeletal deformities.
216
Why does ascorbate (Vitamin C) deficiency cause poor wound healing and easy bleeding?
* Vitamin C required for lysyl hydroxylase to form covalent bonds between fibrillar collagens.
* No covalent bonds = no tensile strength of fibrillar collagens.
* Fibrillar collagens responsible for forming connective tissue in blood vessels and in healing wounds / scars.
* No strength of fibrillar collagens = no strength of connective tissue in blood vessels and wounds = poor wound healing and subsequent easy bleeding.
217
What diseases are associated with collagen and lysyl hydroxylase genetic defects?
* Osteogenesis imperfecta.
* Ehlers-Danlos syndrome.
218
ECM components:
Fibrous structural proteins:
*-Non-Fibrillar collagen examples*
Collagen type:
* IV
* VII
* IX
219
ECM components:
Fibrous structural proteins:
*-Non-fibrillar collagen roles*
* Part of structure of planar basement membranes.
* Helps regulate collagen fibril diametes.
* Helps regulate collagen-collagen interactions via fibril-associated collagen with interrupted triple helices (FACITs).^
* Provide anchoring fibrils that maintain structure of stratified squamous epithelium.^^
## Footnote
^ e.g.Type IX collagen in cartilage.
^^ e.g. tpe VII collagen. Mutations lead to blistering skin disease.
220
ECM components:
Fibrous structural proteins:
*-Elastin structure*
* Cross-linked^ elastin proteins with large hydrophobic segments allowing dense globular configuration at rest.
## Footnote
^Keeps the elastic fibre intact.
221
ECM components:
Fibrous structural proteins:
*-Where is elastin most important*
* Cardiac valves.
* Large blood vessels.
* Uterus.
* Skin.
* Ligaments.
222
ECM components:
Fibrous structural proteins:
*-Elastic Fibre structure*
* Central core of elastin.
* Associated mesh-like network of fibrillin glycoprotein.
223
What is the importance of fibrillin synthetic defects?
* Fibrillin synthetic defects --> defective elastic fibres --> skeletal abnormalities and weakened aortic walls.^
* Fibrillin synthetic defects --> no fibrillin --> no free Transforming growth factor-beta.^^
## Footnote
^ Elastic fibres essential parts of ligaments and large blood vessels.
^^ Pathogenesis of Marfan syndrome.
224
What disease is associated with fibrillin synthetic defects?
Marfan syndrome.
225
ECM components:
Water-hydrated gels:
*-Role*
* Compressive resistance.
* Lubrication.
226
ECM components:
Water-hydrated gels:
*-Main examples*
* Proteoglycans.
* Hyaluronan.
227
ECM components:
Water-hydrated gels:
*-Proteoglycan structure*
* Hyaluronic acid backbone (hyaluronan).
* Intersects with core protein.
* Connected via link proteins.
* Sulfated sugars (glycosaminoglycans)^ extend off core protein like the bristles of a brush.
## Footnote
^ Keratan sulfate and chondroitin sulfate
228
ECM components:
Water-hydrated gels:
*-Role of sulfated sugars in proteoglycan structure*
Attract sodium and water --> generation of a viscous but compressible matrix.
229
ECM components:
Water-hydrated gels:
*-Specific roles of proteoglycans*
* Form highy hydrated compressible gels that allow for resistance to compression.
* In joint cartilage: provide lubrication between bony surfaces.
* Reservoirs for growth factors secreted into the ECM (e.g. fibroblast growth factor [FGF], hepatocyte growth factor [HGF]).
* Integral cell membrane proteins which are involved in cell proliferation, migration and adhesion (by binding and concentrating growth factors and chemokines).
230
ECM components:
Adhesive glycoproteins:
*-Role*
Connect ECM elements to one another and to cells.
231
ECM components:
Adhesive glycoproteins:
*-Main examples*
* Fibronectin.
* Laminin.
* Integrins.
232
ECM components:
Adhesive glycoproteins:
*-Fibronectin location*
Interstitial ECM.
233
ECM components:
Adhesive glycoproteins:
*-Fibronectin structure*
* Large (450-kDa).
* Disulfide-linked heterodimer.
234
ECM components:
Adhesive glycoproteins:
*-What synthesises Fibronectin*
* Fibroblasts.
* Monocytes.
* Endothelium.
235
ECM components:
Adhesive glycoproteins:
*-Fibronectin specific roles*
* Specific domains which bind to distinct ECM components (e.g. collagen, fibrin, heparin, proteoglycans).
* Specific domains which bind to cell integrins.
* Provide the scaffolding for subsequent ECM deposition, angiogenesis and re-epithelialisation in healing wounds.
236
ECM components:
Adhesive glycoproteins:
*-Laminin location*
ECM basement membrane
237
ECM components:
Adhesive glycoproteins:
*-Laminin structure*
* Large (820-kDa).
* Cross-shaped heterotrimer (alpha, beta 1 and beta 2 chains).
238
ECM components:
Adhesive glycoproteins:
*-Laminin specific roles*
* Connects cells to ECM type IV collagen.
* Connects cells to ECM heparan sulfate proteoglycan.
* Modulates cell proliferation, differentiation and motility.
239
ECM components:
Adhesive glycoproteins:
*-What are integrins and what are they also known as*
* Family of transmembrane heterodiameric glycoproteins (i.e. adhesion receptors).
* AKA: cell adhesion molecules (CAMs).^
## Footnote
CAMs also include cadherins and selectins.
240
ECM components:
Adhesive glycoproteins:
*-Integrin structure*
* Transmembrane heterodiameric glycoprotein.
* Alpha and beta subunits.
241
ECM components:
Adhesive glycoproteins:
*-Integrin specific roles*
* Link intracellular cytoskeleton with ECM through allowing cells to attach to ECM laminin and fibronectin.
* Facilitate cell-cell adhesive interactions.
* On leukocytes: mediate firm adhesion to, and migration across, endothelium and epithelium at sites of inflammation.
* Critical role in platelet aggregation.
* Binding can trigger signaling cascades that regulate cell locomotion, proliferation, shape and differentiation.
242
ECM components:
Adhesive glycoproteins:
*-How do integrins attach to ECM components*
Via a tripeptide arginine-glycine-aspartic acid motif (RGD).
