Cells and tissues Flashcards
(258 cards)
1
Q
In what way do cells not live in isolation?
A
In direct contact with neighbours.
2
Q
What is the name for the point of contact between cells?
A
Junctions.
3
Q
What are types of cell junctions?
A
Tight junction, adherens junction, desmosome, gap junction, hemidesmosome.
4
Q
What are organised tissues?
A
Different types of cells grouped together.
5
Q
What is organisation and appearance of cells in tissues like?
A
Closely linked to functions of tissue, easily identified.
6
Q
What do tissues at different positions mean?
A
Different functions.
7
Q
What is the difference between tissues outside, inside and in middle?
A
In contact with environment, with body cavities, most tissues like this respectively.
8
Q
What are the four basic tissues of plants?
A
Dermal tissue, ground tissue, vascular tissue, meristem tissue.
9
Q
What are the four basic tissues of animals?
A
Epithelium, connective tissue, muscle, nerve.
10
Q
What is dermal tissue of plants?
A
Outer layer of roots, stems and leaves (cover), functions as transpiration barrier, gas exchange and defence, includes stomata.
11
Q
What do the stomata allow?
A
Release CO2 and O2, and water vapour.
12
Q
What does the waxy cuticle on surface of leaves do?
A
Lowers transpiration.
13
Q
What are the three types of ground tissues (bulk of plant tissue)?
A
Parenchyma tissue, collenchyma, sclerenchyma.
14
Q
What is ground tissue - parenchyma?
A
Most common, thin primary cell wall, primary component of young plant organs, totipotent, important for regeneration/healing.
15
Q
What does totipotent mean?
A
Differentiate into any cell type.
16
Q
What are functions of grown tissue - parenchyma?
A
Storage of starch and other metabolites, photosynthesis.
17
Q
What is ground tissue - collenchyma?
A
Live mature cells, thicken cell walls, elongated cells that connect together to form resilient strands, beneath epidermis of stems and leaves.
18
Q
What are the functions of collenchyma?
A
Provide adaptable mechanical supports, tissues can change in response to external stimuli e.g. strong wind.
19
Q
What is the ground tissue - sclerenchyma?
A
Cells have primary and secondary cell wall (cellulose and lignin), two types of cells - fibres and sclereids.
20
Q
What does lignin provide to cell walls?
A
Rigidity.
21
Q
What are the fibre cells in sclerenchyma?
A
Long strands, non living, fabric material - hemp and flax.
22
Q
What are the sclereid cells in sclerenchyma?
A
Hard covering around seeds of stone fruits like cherries or walnuts, pear pulp.
23
Q
What is vascular tissue?
A
Plumbing system of a plants - two main types (xylem and phloem).
24
Q
What is xylem and its function?
A
Dead cells at maturity, hollow structure, unidirectional water transport, root - stem leaves.
25
What is phloem and its function?
Transport of nutrients absorbed by roots, sugars made by photosynthesis, multidirectional.
26
What are the meristems and their function?
Sites of active growth, undifferentiated parenchymal cells similar to stem cells, generate new cells that can differentiate, apical for growth of roots and shoots, primary increase length/height secondary make new xylem/phloem.
27
What is tissue?
Collection of cells and extracellular materials specialised for a particular function.
28
Structurally, what are the three types of muscle tissue?
Non-striated involuntary, striated involuntary, striated voluntary.
29
Overview of skeletal muscle tissue?
~640 in adult body, voluntary movements, posture, force generation, attached to bones via tendons, work in pairs to provide movement,
30
Why are skeletal muscle tissues striated?
Because sarcomere is highly organised linear fashion for unidirectional force.
31
What is cardiac muscle tissue?
Involuntary muscle responsible for pumping blood through heart, contracts rhythmically and continuously throughout life, striated branched cylindrical cells connected with intercalated discs, abundant mitochondria for energy.
32
What is the importance of the specialised connections between cells in cardiac muscle tissue?
Allow rapid transmission of electrical impulses, enable synchronised contractions.
33
What is smooth muscle tissue?
Involuntary, non striated, thick and thin filaments not organised in orderly fashion, spindle shaped cells, in blood vessels, intestine, bladder, uterine wall.
34
What are the functions of smooth muscle tissue?
Peristalsis in gut, vasoconstriction in blood vessels, uterine contraction in childbirth, bladder release.
35
What is the role of nerve tissue?
Communication through electrical and chemical signals.
36
What are examples of nerve tissue?
Neurons and glial cells, motor and sensory neurons.
37
What are the two types of nerve tissue?
Central vs peripheral.
38
What is an example of peripheral nerve tissue?
Sciatic nerve.
39
What does nerve tissue consist of?
Motor neurons, sensory neurons and lots of connective tissue.
40
What is the CNS?
Brain and spinal cord.
41
What additional tissue comprises the CNS?
Skull, vertebral column, meninges, cerebrospinal fluid etc…
42
What is connective tissue?
Tissue with cells embedded in extensive extracellular matrix.
43
What mechanical functions does connective tissue serve?
Support, wrapping and binding, packing and space filling, wound healing, storage of energy, infection control.
44
What may connective tissue form?
Structures in their own right e.g. bones and tendons, or part of other tissues or organs.
45
What are the three subcategories of connective tissue and what are some examples?
Loose (adipose), dense (elastic), supportive (cartilage), fluid (blood, lymph).
46
What is bone and what is it made up of structurally?
A living tissue of ECM (collagen), ~90% organic matrix, calcified, highly vascularised and innervated.
47
Why does bone have a high compression resistance and high tension resistance?
Due to calcification and collagen respectively.
48
What types of cells can be found in connective tissue and what are their roles?
Fibroblasts (secrete EM), adipocytes (store lipid as droplets), mesenchymal cells (stem cells to differentiate).
49
What is the function of connective tissue cells?
Secrete matrix, sense loading/tension on matrix, modify matrix according to load.
50
What is ECM comprised of?
Fibres and ground substance.
51
What are the fibres in ECM and their functions?
Collagen for tensile strength and elastic fibres for stretch and recoil.
52
What is the ground substance in connective tissue and what’s its role?
Complex glycosaminoglycans that resist compression.
53
What is the total cell number in an average man?
~3.72 x 10^13
54
What % roughly of body weight is water in an average man?
~ 60% (42 litres).
55
How many litres of internal body water is actually intracellular?
Only 28 litres - rest is connective tissue.
56
What is an organ?
A distinct functional unit formed from 2 or more tissue types.
57
What is an organ system?
A collection of organs with related functions.
58
What comprises the plant shoot system?
Shoot, leaves, stems, flowers, fruits.
59
What comprises the human digestive system?
Mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum, anus.
60
What are the three major cell lineages established within embryo?
Ectoderm (outer), mesoderm (middle), endoderm (inner).
61
From ectoderm, mesoderm and endoderm, which are nervous tissue and muscle tissue?
Ectoderm and mesoderm respectively.
62
How do epithelial tissues originate from all three layers?
Ectoderm = skin, mouth, nose, anus, mesoderm = lymphatic lining, endoderm = airway lining, digestive system.
63
What is the epithelia tissue?
Tissue that cover and line the interior and exterior surfaces of the body e.g. skin.
64
What are the three categories to describe the shape of the top layer of epithelia?
Squamous (flat), cuboidal (square), columnar (elongated columns).
65
What are the three categories to describe the number of layers of epithelia?
Simple (one), stratified (multiple), pseudostratified (one layer but nuclei at different levels - only in columnar).
66
What is classification of epithelia based off?
Shape and how they’re stacked together.
67
What are simple squamous epithelium’s structure, functions and examples?
Composed of single layer of cells, flat and plate like, nuclear appear flattened, allows passage of materials through diffusion, e.g. alveoli.
68
What are simple cuboidal epithelium’s structure, functions and examples?
Single layer cube like cells, large spherical central nuclei, nephrons lining, renal tubules, secrete and absorb.
69
What are simple columnar epithelium's structure, functions and examples?
Single layer columnar cells, oval shaped nuclei in basal region, digestive tracts, fallopian tubes, secrete and absorb.
70
What are stratified squamous epithelium’s structure, functions and examples?
Classification based on shape of top layer, columnar or cuboidal in deeper layer, keratinised or non-keratinised, areas under constant abrasion.
71
What is non-keratinised stratified squamous epithelium?
Top layer living and nucleated cells, need constant moisture to prevent drying out, lining of oral cavity.
72
What is keratinised stratified squamous epithelium?
Dead cells, tough, impermeable, protective layer of top cells, mechanically strong, inert but flexible, tissue facing regular abrasion e.g. skin.
73
What is keratinisation?
A process by which the cytoskeleton of cells in top layer becomes tightly condensed with keratin.
74
What are stratified columnar and cuboidal epithelium?
More than one layer of cells.
75
What is pseudostratified epithelium?
Positioning of nuclei makes single cell layer look stratified, all cells in contact with ECM, e.g. bronchi lining, trachea.
76
What is transitional epithelium and its importance?
Special type of stratified, can change shape, multiple layers of cells that can contract and expand to accommodate different degrees of distension, e.g. bladder, allows tissue stretching depending on volume.
77
What shapes can transitional epithelium change between and how?
Cuboidal when cells are relaxed and squamous when cells are stretched.
78
What does the glandular epithelium structure mean?
Epithelium grows as a tube into underlying tissue (not just on surface).
79
What does the glandular epithelium structure form?
Specialised secretory gland structure - exocrine gland e.g. mammary gland.
80
Explain how the glandular epithelium structure can be heterogenous?
Different cell types, additional types interspersed among epithelial cells e.g. goblet cells for mucus secretion.
81
What are the four key common features of epithelia?
Cellularity, specialised intercelular contacts, cell polarity, basement membrane.
82
What does the epithelial cellularity mean?
Entirely cellular, single layer or multiple, cell layer separates internal and external environment.
83
What does the cellular layer of epithelia allow for?
Regulation of material transfer between two interfaces.
84
What are tight junctions and their function?
Tight seals to prevent leakage of water soluble molecules through gaps between cells (leak proof).
85
What is the importance of tight junctions and some examples?
Forces material to pass through cells rather than between e.g. BBB, gut epithelium.
86
What are the three main types of anchoring junctions?
Adherens, desmosomes, hemidesmosomes.
87
What is the function of anchoring junctions?
Form strong mechanical attachments between cells.
88
How are anchoring junctions formed?
Built around transmembrane proteins, cadherin protein superfamily, cadherin binds directly to identical molecule of neighbour, homophonic binding requires Ca2+ present in extracellular medium.
89
Intracellularly, what is cadherin tethered to?
Cytoskeletal filaments via linker proteins.
90
How are adherens junctions formed?
Each cadherin molecule tethered to actin filaments that are tied into a network that extend from cell to cell across entire epithelial sheets, filaments remain intracellular.
91
What do adherens junctions + actin bundles form?
Often form continuous adhesion belt near apical end of each interacting epithelial cells.
92
What is the importance of adherens junctions?
Provide strong mechanical stability to epithelial sheet.
93
What are desmosomes extracellularly?
Cadherin-cadherin interaction.
94
What are desmosomes intracellularly?
Cadherin interacts with cytoplasmic plaque (linker proteins) that provide anchor for intermediate filaments (keratin).
95
Where are desmosomes found?
Specifically in epithelial cells.
96
What is the role and importance of desmosomes?
Used for rope-like keratin filaments to criss-cross cytoplasm and weld to keratin filaments in adjacent cells, confer great tensile strength to epithelial sheet.
97
Where are keratin filaments found?
Within the cells, do not enter adjacent cells physically.
98
What is pemphigus that occurs due to burning?
Autoantibodies attack desmoglein (cadherin), cells separate, epidermis detached, blisters form, can be fatal but varies.
99
Compared to adherens and desmosomes being cell-cell interactions, what are hemidesmosomes?
Cell-basal lamina interactions.
100
How are hemidesmosomes formed?
Built via integrin protein (transmembrane), integrin cytoplasmic tail interacts with intermediate filaments (keratin), integrin extracellular domain binds to basal lamina (ECM).
101
What does the hemidesmosomes structure look like that gives it its name?
Looks like half of a desmosome hence ‘hemi’.
102
What is the importance of hemidesmosomes?
Connects cells to connective tissue.
103
What do gap junctions do?
Bridge a very narrow gap of 2-4nm between plasma membrane of adjacent cells, allow inorganic ions and other small water soluble molecules through, connect cells for electrical or metabolic flow.
104
How are gap junctions formed structurally?
Spanned by protruding ends of transmembrane protein complexes (connexons), aligned end to end to form water filled channels, made of clusters of six protein subunit arrange as a tube.
105
What signals can gap junctions flip between open and closed states according to?
Electrical, pH change, neurotransmitter signals.
106
Give some examples of uses of gap junctions.
Synchronous beating of cardiac muscle cells, ciliary beating in lung epithelium, islet of langerhans of pancreas coordinated secretion, dopamine induce reduction in communication in response to bright light.
107
What is the name for the top surface of epithelia?
Apical (external environment).
108
What is the name of the bottom surface of epithelia?
Basal (basement membrane).
109
What cell surface specialisations on apical and basal membranes increases total surface area of both?
Cilia and microvilli on apical, basal fold on basal.
110
What do epithelial cells sit on top of?
Basement membrane (basal lamina).
111
What’s underneath the basement membrane?
Connective tissues.
112
What extracellular matrices does the basement membrane consist of?
Type IV collagen, laminin (glycoprotein), perlecan (proteoglycan).
113
What are some overall common features of epithelia?
Completely cellular layer, little or no ECM between cells, joined by junctions, avascular, sit on basement membrane, over vascular connective tissue, controls entry exit of materials.
114
What are the five general functions of epithelia?
Protection (physical barrier), absorption (specialised surface structure), secretion (adaptation to secrete macromolecules), dialysis (kidney and lung epithelium), sensation (taste buds, olfactory epithelium).
115
What cells give rise to a tumour?
Cells that lose their normal growth control mechanism (neoplasm).
116
What is a carcinoma?
Malignant tumour derived from epithelium.
117
What are the malignant neoplasms of squamous epithelium and glandular epithelium?
Squamous carcinoma and adenocarcinoma.
118
What forces are experienced by connective tissues?
Compression, tension, shear.
119
What are the functions of loose connective tissue?
Space filling and binding, energy storage, cushioning, allows planes of movement, immune function.
120
What is loose connective tissue composed of?
Fibres (collagen and elastic), ground substances (polysaccharides), loose connective tissue cells.
121
What are the roles of adipose loose connective tissue?
Energy storage, insulation and protection, heat generation.
122
What are the roles of areolar loose connective tissue?
Widely distributed, e.g. subcutaneous layer around blood vessels etc, structural support.
123
What is reticular loose connective tissue and its role?
Made of reticular fibres that form mesh-like network, structural support, spaces to enable cell movement.
124
What are the different types of resident cells in loose connective tissue?
Fibroblast, adipocytes, mast cells, endothelial cells, pericytes.
125
What are fibroblasts?
Most abundant resident cells, secrete polysaccharides and protein, form ECM.
126
What are adipocytes?
Resident cells, store lipids as droplets, two basic types -white and brown.
127
What are mast cells?
Have many cytoplasmic granules, e.g. histamine, histamine release for inflammatory response.
128
What are endothelial cells and pericytes?
Thin, tightly joined, barrier function, pericytes maintain stability and integrity of capillary.
129
What are the different types of immigrant cells in loose connective tissue?
Monocytes, macrophages, lymphocytes.
130
What are monocytes?
Migrate to loose CT upon immune response, circulate in bloodstream (surveillance), differentiate into macrophages or dendritic cells.
131
What are macrophages?
Carry out phagocytosis, present antigen to T-cell.
132
What are lymphocytes?
Constantly circulate between blood, lymphoid organs and loose connective tissue.
133
What are examples of lymphocytes and their functions?
T cell (direct attack on pathogen), B cell (form plasma cells that produce antibodies), natural killer cells, attract to site of infection by chemotactic signals.
134
What is dense CT like compared to loose CT?
Contains more collagen fibre, greater resistance to stretching.
135
What are the two major types of dense CT?
Regular and irregular.
136
What are characteristics of regular dense CT?
Fibres parallel, enhanced tensile strength, resistance to stretching highly directional, may have elastin fibres, e.g. ligaments and tendons.
137
What are characteristics of irregular dense CT?
Direction of fibres random, greater resistance to stretching in all directions (multi-direction), e.g. dermis of skin, arterial wall.
138
What are the functions of cartilage?
Connecting bones, cushioning joints (articulations), protecting the ends of bones, providing shock absorption.
139
Why does cartilage have a distinctive appearance?
Due to polysaccharide called chondroitin sulphate (proteoglycan).
140
What are the three types of cartilage?
Hyaline (most common), elastic, fibrocartilage.
141
What is Hyaline cartilage like structurally?
Consists of short and dispersed collagen fibres, large amount of proteoglycans, glass like (clear), smooth, strong, flexible, resist compression, stiff.
142
Where is hyaline cartilage located?
Joint surfaces (adult), foetal skeleton, tracheal rings.
143
What does “chondro” mean?
Cartilage.
144
What does “cytes” mean?
Cells.
145
What are chondrocytes?
Cartilage cells.
146
What’s the lacunae?
Holes that chondrocytes live in.
147
What is the hyaline cartilage matrix rich in?
Proteoglycans.
148
What are chondrocytes capable of and what does this mean?
Division, cartilage grows faster than bone.
149
What is appositional growth?
From perichondrium, girth expansion, thickening.
150
What is interstitial growth?
Expansion from within tissue.
151
What is the role of chondrocytes?
Secrete and interact with ECM.
152
What are the main classes of ECM found in hyaline cartilage?
Collagen fibres, proteoglycans (absorbs water).
153
What are cells and fibres like at articular surface, what does this cause?
Cells flatter and collagen fibres are organised parallel to surface - resist shear force.
154
What are cells and fibres like deeper in tissue, what does this cause?
Arrange roughly perpendicular to articular surfaces - proteoglycans draws water in creating outward pressure, resists compression forces.
155
What are the components of elastic cartilage?
Collagen fibres, proteoglycans, elastic fibres.
156
What is elastic cartilage like?
Has rigidity and elasticity (bounces back to original shape).
157
Where is elastic cartilage located?
Pinna of ear, epiglottis.
158
What is fibrocartilage?
Intermediate between hyaline cartilage and dense fibrous connective tissue, stiff, compression resistance and high tensile strength.
159
How is fibrocartilage visibly fibrous?
Very high collagen fibre content, intermediate proteoglycan.
160
Where is fibrocartilage typically located?
At tissues experiencing compression like intervertebral disc, temporomandibular joint, meniscus in knee joint.
161
What forms spongy bone?
Slender bony projections (trabeculae).
162
What forms compact bone?
Organised into osteons, circular structure surrounding central canal, blood vessels, nerves, lymphatic vessels pass through.
163
What are the four types of bone cells?
Osteogenic cells (precursor), osteoblast, osteocytes, osteoclasts.
164
What are osteogenic cells?
Undifferentiated cells that divide, found in deep layers of periosteum and marrow, differentiate into osteoblasts.
165
What are osteoblasts?
Form new bones, don't divide, synthesise and secrete collagen matrix and calcium salts.
166
What are osteocytes?
Formed from osteoblasts after matrix calcification, cells embedded in calcified bone matrix, maintain mineral conc of matrix.
167
What are osteoclasts?
Found on bone surfaces, multinucleated and originated from WBCs, responsible for bone resorption.
168
What is bone resorption?
Breakdown?
169
What is ossification?
Formation of bones.
170
What is endochondral ossification?
Formation of bones from pre-existing cartilage template.
171
What is intramembranous ossification?
Formation of bones without going through cartilage intermediate.
172
What is intramembranous ossification and an example of it?
Bone formation directly from mesenchymal stem cells without cartilage intermediate e.g. flat bones such as skull or facial.
173
How does intramembranous ossification take place?
Mesenchymal stem cells condense to form a dense mass, differentiate into osteoblasts, osteoblasts secrete bone matrix that calcifies and traps then in lacuna, further differentiation into cytes, remodelling with clasts forms spongy bone via vascularisation.
174
What kind of bones does endochondral ossification form, give an example?
Long bones, e.g.femur, tibia, humerus.
175
How does endochondral ossification take place?
Mesenchymal cells differentiate into chondroblasts - produce hyaline cartilage model of future bone, cartilage grows by interstitial and appositional growth.
176
Where is the primary ossification centre?
Diaphysis (shaft of bone).
177
What is the secondary ossification centre?
Epiphysis (heads of bone).
178
What happens at the primary ossification centre?
Chondrocyte condense, enlarge, cartilage matrix calcifies, blood vessels invade, brin osteoblasts and clasts, blasts replace calcified cartilage with spongy bones.
179
What happens at the secondary ossification centre?
At birth, blood vessels and osteoprogenitor cells grow into epiphyses.
180
What does cartilage at ends of bones form?
Articular cartilage.
181
What does cartilage at junctions form?
Epiphyseal plate (growth plate), allowing growth in length.
182
What is the epiphyseal cartilage (growth plate)?
Hyaline cartilage with unique organisation, cells in column.
183
What are the first three steps of the developmental process at epiphyseal cartilage?
Resting chondrocyte receives signal from growth hormones, proliferate in columns towards diaphysis, in hypertrophic zone cells grow larger, secrete calcified matrix.
184
What are the last four steps of the developmental process at epiphyseal cartilage?
Calcified cartilage, cuts of nutrient supply, chondrocytes undergo apoptosis, leave behind lacunae, scaffold for osteoblast invasion, blood vessels and more blasts, deposition of bone matrix, replacing cartilage with true bone tissue.
185
What is the ECM??
Extracellular matrix, outside cell, materials released and assemble into 3D structures.
186
What are common features of ECM?
Fibrous network and gel-like background matrix, saccharides present.
187
What are common features of ECM for plants?
Polysaccharide fibres embedded in matrix of highly charged pectin polymers.
188
What are common features of ECM for animals?
Fibrous proteins fibres embedded in matrix of highly charged glycosaminoglycans.
189
What is the thick layer of specialised ECM that surrounds all plant cells?
Cell wall.
190
What is plant ECM made up almost entirely of?
Carbs + small amount of proteins.
191
What are the principal fibrous components of plant ECM?
Thick fibres are cellulose, crosslinked by hemicellulose.
192
What is the complex -ve charged polysaccharide gel that fibrous components are embedded in for plant ECM?
Pectins.
193
What is the importance of the plant cell wall?
Gives rigidity and strength.
194
How does the plant cell wall work in association with turgor pressure?
Osmosis draws water into cells, turgor pressure pushing outward, cell wall stretched.
195
Why do plants wilt without enough water?
Loss of turgor pressure, cell wall not stretched, structure lose its strength.
196
What are some parts of plants reinforced with?
Extra cell wall, stronger and independent of turgor pressure.
197
What is the three layered structure of plant cell wall?
Primary cell wall, secondary CW, middle lamella.
198
When does the middle lamella form and what does it do?
Forms after cell division, fusion of vesicles with components, glues cells together, allows plasmodesmata to form.
199
In what order are the primary CW and secondary CW synthesised after middle lamella?
Primary second, secondary last (not all cells have this).
200
What cannot happen after secondary CW forms?
Cells will no longer divide.
201
What is the middle lamella?
A uniform and continuous layer between adjacent cell wall, glue to bind adjacent cells.
202
What is the structural composition of middle lamella?
Pectins and proteins, pectin made of chains of galacturonic acid molecules, highly charged as hydrated so forms gels with Ca2+ and Mg2+.
203
What happens when the first CW is produced?
Pushes middle lamella away from plasma membrane.
204
What are key properties of primary CW?
Expandable - allow cell growth/enlargement, semi-permeable - passage of nutrient and air.
205
What is the cellulose of primary CW like?
Straight chain glucose polymer thick rigid micro fibrils, highly ordered structure, high tensile strength.
206
What is the hemicellulose that composes primary CW like?
Branched chain of sugar polymer, crosslinking cellulose micro fibril, pectin, proteins.
207
Where does the secondary CW form and when?
Between plasma membrane and primary cell wall, after cell stopped expanding and primary CW finished.
208
What are the components of secondary CW?
Cellulose fibres, lignin, pectin not always present, no protein.
209
How can secondary CW cause cell death?
If too thick, gives high tensile/compressive resistance.
210
What are the three major ECM classes?
Tensile strength elasticity, space filling, glue like.
211
What is collagen and its role?
Most abundant protein found in mammal - about 25-30% total protein mass, main structural component of ECM, provides tensile strength.
212
How many different classes of collagen superfamily in vertebrates are there and how are they different?
~28, distinct molecular structure and organisation, functions in different tissues.
213
Where can collagen be found?
In skin, bone, cartilage, tendon, ligament, vasculature, basement membrane.
214
What is the composition of collagen?
Triple stranded helix, long stiff rope-like, made up of three collagen alpha chains, right handed winding around each other and another single alpha chain.
215
What is the singular a-chain in collagen, separate from the three winded together, like structurally?
A left handed helix, contains amino acid triplet repeat (G-X-Y).
216
What is collagen rich in and why is this important?
Glycine and proline, for triple helix formation.
217
What do all collagen molecules contain?
Triple helical region - at least ONE helical domain.
218
What do the structural components of collagen allow for?
Extremely stable structure e.g. bone collagen.
219
What stabilises interactions between helices?
Hydrogen bonds.
220
How many different genes are there to code for different a-chains of collagen in vertebrates?
45.
221
What are different classifications of collagen?
Fibrillar collagen, FACIT, network, hexagonal networks, beaded filaments, anchoring fibrils, filamentous.
222
What does FACIT stand for?
Fibrillation-associated collagen with interrupted triple helix.
223
How is type 1 fibrillar collagen synthesised intracellularly?
Translation, proline and lysine hydroxylation, triple helix formation (procollagen), secretion.
224
How is type 1 fibrillar collagen synthesised extracellularly?
Cleavage of N and C-pro peptide - tropocollagen, quarter staggered array arrangement, crosslink formation.
225
What is network collagen (IV) like structurally?
Contains triple helix with several non-triple helical sections, N- and C- terminal globular domains.
226
What does network collagen not do?
Does not cleave at both termini during synthesis, does not form fibrils.
227
How do type IV collagen molecules assemble?
Via globular domains to form network structures.
228
Where is network collagen found?
Main collagen in basement membrane (a thin sheet-like structure that underlies epithelial and endothelial cells).
229
What are primary functions of type IV collagen?
Structural support (tensile strength to membrane), cell adhesion (act as substrate for attachment and migration), filtration barrier.
230
What is the role of elastic fibre?
Provide elasticity to tissues e.g. skin, enable recoil after transient stretch, interwoven with inelastic collagen fibre to limit stretching and tearing.
231
What is elastin fibre made of?
Elastin + micro fibrils, repeating hydrophobic pentapeptides, alternating phobic-philic domain, elastin joined covalently generating crosslinks, each extends and contracts like coil.
232
What are exposed on elastic fibre when stretched and what does this promote?
Beta-spiral hydrophobic regions, promotes recoil.
233
What does genetic mutation in collagen structure or synthesis cause?
Disrupts balance between collagen - tensile and elastin - elastic, collagen function affected, hyperelasticity of skin/ligaments.
234
What are glycosaminoglycan (GAG) and proteoglycan?
Highly hydrated gel-like matrices that fill EC space, interact with cells collagens factors, absorb compressive forces.
235
What is the structure of GAG/
Unbranched polysaccharide chain, repeating disaccharide unit (amino sugar + uronic acid).
236
What properties does GAG have?
Highly -ve (sulphate or carboxyl), hydrophilic (draw water into matrix).
237
What does the -ve charge of GAG promote?
Extended conformation - occupies large volume.
238
What is the significance of GAG being gel-like?
Withstands compressive forces.
239
What is hyaluronan?
Hyaluronic acid, simplest form of GAG, identical disaccharide unit, no sulphate sugar, n-acetylglucosamine + glucuronic acid.
240
What are two key characteristics of hyaluronan?
Enormous chain length - up to 25,000 disaccharide units, bulky and hydrated - fulfil space-filling functions.
241
What are the four principal functions of hyaluronan?
Maintain osmotic pressure by cation binding, lubricant, development, wound healing.
242
What are proteoglycans like structurally?
Protein core + glycosaminoglycan (GAG), covalently joined to protein core.
243
What is an example of a proteoglycan and what’s its role?
Aggrecan, aggregates 1 hyaluronan chain, 30-50 aggrecan monomers, 30-50 link proteins.
244
What is aggrecan like structurally and functionally?
All interactions non-covalent, ~80-100 million dalton, binds water (-ve GAG), aggregates form densely packed hydrated gel, major component of cartilage.
245
What is the function of aggrecan in cartilage under compression?
Water displaced, aggrecan aggregates are compressed.
246
What is the function of aggrecan in cartilage upon relaxation?
Water rebinds aggrecan, tissue swells.
247
Why is collagen fibrils resisting excessive swelling important?
Maintains tissue integrity.
248
What is aggrecan the principal of?
Principal load-bearing proteoglycan in cartilage.
249
In what way does aggrecan help cells withstand mechanical load?
Aggregates bind water (swell) creating high osmotic pressure.
250
What are glycoproteins like structurally?
Proteins + sugar side chain, relatively short, branched oligosaccharide side chain.
251
What contributes to a small fraction of glycoproteins mass?
Oligosaccharide side chain.
252
In what way do glycoproteins have adhesive properties?
Bind cells and ECM to form network, e.g. fibronectin and laminin.
253
Why can fibronectin be described as a multidomain glycoprotein?
Binds different substrates e.g. collagen, integran, heparan sulphate.
254
What are structural functions of fibronectin?
Organisation and stabilisation of ECM network (adhesion), adhesive - enables cell attachment (migration).
255
How is fibronectin formed?
Seeded on matrigel (basement membrane), focal adhesion translocation towards cell centre, assembles fibronectin immediately behind.
256
What is laminin like structurally?
Heterotrimer (alpha, beta, gamma chains), multidomain glycoprotein (self assembly, integrin, perlecan, nidogen.
257
What does laminin polymerisation initiate?
Basal lamina formation.
258
What is the role of laminin?
Form flexible permeable layer underpinning endothelial and epithelial cells, link cellular layer with loose connective tissue.
