MOLECULAR GENETICS AND CELL BIOLOGY Flashcards
(110 cards)
1
Q
what are the functions of skeletal muscles
A
connects the skeleton
allows complex coordinated activities
rapid contraction/relaxation
2
Q
what is the difference between an isotonic contraction and a isomeric contraction
A
isotonic causes movement whereas isomeric contractions allow muscles to be immobile
3
Q
what is the structure of a skeletal muscle
A
muscle fibre–sarcolemma(muscle cell membrane)–myofibril
4
Q
what is the muscle term for cell membrane
A
sarcolemma
5
Q
what is the msucle term for cytoplasm
A
sarcoplasm
6
Q
what is the muscle term for smooth ER
A
sarcoplasmic reticulum
7
Q
what is the muscle term for mitochondrion
A
sarcosome
8
Q
what is the muscle term for nucleus
A
myonuclei
9
Q
are myofibres multinucleated or uninuleated
A
multinucleated
10
Q
what are the divisions of the myofibrils caused by and what are they called
A
caused by myofilaments A bands-dark bands H bands-dark area bisecting A bands I band-light area Z disk/line-light area bisecting I band
11
Q
where is the sarcomere located
A
segment between Z disks
12
Q
what is the thick filament mainly composed of
A
myosin
13
Q
is the thick filament polar
A
yes it is bipolar with the heads at distal tips and teails at the centre
14
Q
what is the thin filament made of
A
mainly actin but also tropomyosin and troponin
15
Q
how are the thin filaments oriented
A
one end bound to the Z disk with the other ens near the centre of sarcomere
16
Q
what protects the actin (thin filament) from depolymerizing
A
the capZ at the head end and the tropomodulin at the tail end
17
Q
how to the thin and thick filaments cross over
A
the head of the myosin molecules potrude from the th AI zone. the thick filaments then form cross bridges with adjacent actin thin filaments
18
Q
is smooth muscle multi or uni nucleated
A
uninucleated
19
Q
does is contain thick and thin filaments
A
yes but they are not organized into sarcomeres and myofibrils and not striated
20
Q
how is the smooth muscle connected
A
is forms loose bundles and attaches to dense bodies. one end of the thin filament is attcahed to the dense bodies whereas the other end is connected to the attachment plaques.
21
Q
what features allow the smooth muscle to be packed so thin and tightly `
A
has a high conc of alpha actinin. the intermediate filaments and dense bodies create a network bound to adherens junctions in the cell membrane
22
Q
features of cardiac muscle
A
striated and organised in sarcomeres
shorter than skeletal muscles
uninucleated located in the centre
connected by intercalated discs
23
Q
what are two structures in the intercalated discs in the cardiac muscle
A
gap junctions and desosomes
24
Q
what are gap junctions
A
forms channels between adjacent cardiac muscle fibres allowing depolarizing current to flow between cardiac muscle cells (electric coupling). functional unit of contraction is a syncytium
25
what are desmosomes
anchors ends of cardiac muscle fibres togetehr so the cells do not pull apart during the stress of individual fibres contracting
26
what does the sliding filament model mean
- the muscle shortening due to the movement of the actin filament over the myosin filament
- the formation of cross bridges between actin and myosin fibres
- reduction in distance between Z-lines of sarcomere
27
how do muscles contract
the myosin heads have ADP and a phosphate attached to them. When a person wants to move calcium is released from the sarcoplasmic reticulum and bind onto open triponin molecules. this causes the trypomison to move revealing myosin attcahment sites on the actin myofilaments. The single phosphate is released and the actin and myosin heads form a crossbridge. the ADP is expended in a power stroke when the myosin heads pull the actin inward. The ATP attaching to the myosin head triggers the bridge to pull apart and the ATP is again broken down into ADP and a phosphate. continues again and again if calcium is still present as the muscle contracts
28
what is titin/connectin
it is a protein with elastic properties. it is there to hold the thick and thin filaments together so that when the muscle stretches they do not lose contact
29
what initiates muscle contraction
it is initiated by an increase in cytosolic calcium ions. skeletal muscles cells maintain low cytosolic calcium ion level by continually pumping using ca2+ ATPase from the cystol to the sarcoplasmic reticulum. this establishes a reservoir of calcium in the sarcoplasmic reticulum
30
what is a neuromuscular junction
it is the site where motor neuron meets muscle fibre and is separated by gap called the neuromuscular cleft
31
what is a motor end plate
pocket formed around motor neuron by sarcolemma (cell membrane)
32
what causes an end plate potential
acetylcholine is released from the motor neuron and causes an end plate potential EPP
33
what happens during end plate potential
when the acetylcholine is released it causes depolarization and the skeletal muscle cells then have to convert it into cytosolic ca2+ which initiates contraction.
34
how does the depolarisation signal move
passed through T (transverse) tubules
35
what is the function of the T tubules
cause the release of the stored calcium into the cytosol via the calcium ion channels in the sarcoplasmic reticulum membrane and this causes contraction within milliseconds
36
how do muscles stop contracting
when the channels close and the ca2+ is pumped back into the sarcoplasmic reticulum
37
what is connective tissue
provides support and binds together and protects tissues/ organs
38
what does connective tissue consist of
fibres
amorphous ground substance- usually a fluid but can be mineralized and solid eg in bones.
composed of polysaccharides mainly hyaluronic acid and proteins which combine to form a proteoglycan which traps moisture
39
what are the functions of connective tissue
- sheath surrounding muscle cells
- tendons attach muscle to bones
- skeleton
- fibrous capsules and bones protecting delicate organs
- defence against microorganisms
40
where does connective tissue come from
derived from the mesodermal layer of an embryo
41
what is fluid connective tissue
various specialized cells circulating in water fluid containing salts, nutrients and dissolved proteins eg lymph and blood
42
what is adipose tissue
consists mostly of fat storage cells with little extracellular matrix
43
what is supportive connective tissue
provide structure and support eg bone, cartilage and teeth
44
what is connective tissue proper
variety of cell types and protein fibres suspened in viscous ground substance
45
what is the difference between loose and dense connective tissue
loose connective tissue is loosely organised fibres with large spaces between and dense connective tissue is reinforced by bundles of fibres providing tensile strength, elasticity and protection
46
examples of specialized connective tissues
cartilage, bone, adipose tissue, haemopoietic tissue and lymphatic tissue
47
what is present in connective tissue proper
- fibroblasts in all connective tissue proper
- adipocytes
- mesenchymal
48
what are fibroblasts
normally spindle shaped cells with oval flat nucleus
found in interstitial space
primary source of extracellular matrix ECM proteins
49
what are adipocytes
store lipids as droplets that fill the cytoplasm
brown adipocytes store lipids as many droplets and have high metabolic activity whereas white adipocytes store them as single large drop and are metabolically less active
50
what are mesenchymal cells
multipotent adult stem cells
| differentiate into any type of connective tissue cells for repair of damaged tissue
51
what are the three types of fibres secreted by fibroblasts
collagen fibres, elastic fibres and reticular fibres
52
which type of collagen is most abundant protein in all vertebrae
type I collagen assembles into fibres that form structural and mechanical scaffold of bone, skin, tendons, cornea, blood vessels and other connective tissue
- it is flexible and has great tensile strength
53
describe the structure of type 1 collagen
type 1 is a heterotrimer meaning it has three sub units
it has intramolecular hydrogen bonds between adjacent chains and stabalizes the triple helix
each alpha chain is left handed but when they are staggered by one residue relative to each other around a central axis they form a right handed superhelix
54
what are elastic fibres
thinner than collagen fibres and arranged i branching pattern to form 3D network
interwoven with collagen fibres to limit distensibility and prevent tearing
composed of elastin and fibrillin
55
what is elastin
related to collagen but coiled elastin molecule can be streched and will recoil
elastin molecules covalently bond to one another and form an elastin matrix
56
what is fibrillin
fibrillar glycoprotein
| appears before the elastin and is believed to serve as an organizing structure
57
what are reticular fibres
formed from type III collagen fibres
fibres remain narrow and arrayed in a branching network
found throughout the body but most abundant in reticular tissue of soft organs where they provide structural support
58
what is the function of loose connective tissue
- found between many organs where it acts both to absorb shock and bind to tissues together
- fills spaces between muscle fibres
- surrounds blood and lymph vessels
- underlies most epithelia
- allows water salts and various nutrients to diffuse through to adjacent or imbedded cells and tissues
59
what are the two categories of dense connective tissue
regular eg ligaments and tendons
| irregular eg epidermis
60
difference between dense and loose connective tissue
dense has more collagen so it has more resistance to stretching
61
describe dense irregular connective tissue
- contains type 1 collagen fibres woven in multiple directions and this provides tensile strength
- it can stretch in several directions by the fibres criss crossing and forming a mesh layer as well as alternating layers where fibres run in the same orientation but at an angle
62
what kind of cells make up the skin
stratified squamous epithelium
63
what is the skin made up of
epidermis
basement membrane zone
dermis
subcutaneous tissue
64
what is an acid mantle
created by acidic substances eg amino acids, lactic acid and fatty acids in perspiration, sebum and hormones
65
what are friction ridges
criss-crossing ridges and valleys. protrusions of the epidermis layer into the upper layers of the underlying dermis
66
what are the three main types of epidermis cells
keratinocytes (skin cells)
melanocytes (pigement cells )
langerhans cells (immune cells )
67
keratinocytes
-normally renewed every 15-30 days
-created in the basal layer and gradually moved upwards
produce keratin
-keratinization- replacement of cell contents with the protein keratin
68
melanocytes
- precursors of melanoblasts
- highly dendritic and pigmented cells
- produce melanin
- melanocyte stem cells reside in hair follicle bulge
69
langerhans
- first line of immunologic defence in the skin
- derive from monocyte-macrophage lineage
- migrate to the lymph nodes and are responsible for allergen recognition
70
merkel cells
-found mainly in the stratum basale of palms,soles,oral and genital mucosa
-contain intracytoplasmic dense core neurosecretory granules as well as neurofilaments and keratin
cause sensations
71
what connects merkels and keratinocytes
desosomes
72
what are the epidermal layers (bottom layer to top )
```
stratum basale ( basal layer)
stratum spinosum (spinous layer )
stratum granulosum (granular layer )
stratum lucidum
startum corneum (horny layer )
```
73
what is in the stratum
| basale
located adjacent to the dermis
attached to the basement membrane by hemidesmosomes
contains melanocytes (1:10 to keratinocytes )
merkel cells very low numbers
74
what is in the stratum spinosum
5-12 layers of polygonal keratinocytes that become flatter near the surface
langerhans are mainly found in this layer
cells are connected by desmosomes
75
what is in the stratum granulosum
3-5 layers of flattened cells
anucleated and losing cytoplasm appear granular at this level
filled with irregular dark keratohyaline granules which are insoluble ( crosslinked keratin filaments )
76
what is in the stratum corneum
flattened dead cells with no nuclei or organelles
| 10-30 layers of stacked corneocytes in most areas
77
what is the basement membrane
thin, dense sheets of specialized, self assembled extracellular matrix
helps to anchor cells to the underlying tissue
78
what are the two independent polymeric networks of the basement membrane
laminin and type IV collagen
79
what are the three distinct layers of the basal lamina (basement membrane)
lamina lucida
lamina densa
lamina reticularis
80
what cells are in the dermis
mast cells
vascular smooth muscle cells
specialised muscle cells
fibroblasts
81
how do the dermis and epidermis communicate
through release of cytokines and chemotactic factors
82
what are the two layers of the dermis
papillary layer- composed of loose connective tissue and blood capillaries most of the touch receptors too
reticular layer- composed of interlacing bundles of collagen and elastin for strength
binds the epidermis to the subcutaneous layer
83
what type touch receptors are located in the dermis
pacinian corpuscle- heavy pressure
meissners corpuscle-light touch
merkels disk-light touch
ruffinis corpuscle- touch, heat
84
what are the parts of the nail
lunulu-half moon shaped portion due to no capillaries beneath it
nail bed- mitotic cells producing the nail
cuticle- layer of tissue seperating the nail from the normal epidermis
85
where do the sweat glands originate from
the dermis/ subcutaneous layer
86
what are the two types of sweat glands
apocrine- respond to emotional distress and sexual stimulation
type of sweat gland
concentrated at the axilla and groin found only with hair follicles
eccrine- found in all skin
respond to elevated body temp
87
what are the characteristics of the sarcoplasmic reticulum
- specific form of endoplasmic reticulum
- ca+ ion pumps and stores ca2+
- no ribosomes
88
what happens at the T tubule
- the action potential reaches down the tubule
- t tubule connected to sarcoplasmic reticulum by protein complex
- protein complex triggers the release of ca+ from the sarcoplasmic reticulum
89
what is the resting potential
-70mV
90
which ion moves in and which one moves out
sodium has influx and potassium has eflux
91
what is the threshold potential
-55mV
92
how does an action potential get generated
if there is a stimulus the sodium VGC open and this causes a rapid influx of sodium ions causing the membrane to be depolarized and if this goes above the threshold potential and action potential is generated. the sodium VGC then close and the potassium VGC open causing a rapid eflux of potassium ions which causes the membrane to be depolarized and so as the potassium VGC close slowly it causes hyper polarization which is fixed by the sodium potassium pump
93
What type of transporter is the Na/K-ATPase
active transporter
94
When the molecule is active and transports ions, what happens to the Na/K-ATPase
the transporter opens and closes
95
what is passive transept
transport with the concentration gradient
96
what is a synapse
the point of contact between a nerve cell and another or a nerve cell and a target cell
97
what is the difference between an electrical and a chemical synapse
the electrical synapse is formed by gap junctions between two neurons and an electrical current can flow directly whereas a chemical synapse the signal is transmitted via neurotransmitters
98
how does a chemical synapse function
the action potential arrives at the presynaptic membrane and this activates the ca2+ VGC and this causes an influx of ca2+ ions. this causes the presynaptic vesicles to release the neurotransmitter substance by exocytosis and this then binds to the receptors on the post synaptic membrane
99
how is the transmitter released
the ca2+ binds to the synaptotagmin and this initiates the fusion with the plasma membrane
100
how do the vesicles fuse
they are facilitated by SNARE proteins which are anchored membrane proteins
101
how is the membrane recycled at the synapse
- membrane fusion by kiss and ru
- the membrane is recycled via clathrin-mediated endocytosis
- pool of docked vesicles can be exchanged and are quality controlled
- recycling via invagination is much slower
102
what is a neuromuscular junction
specialized chemical synapse between motor neuron and skeletal muscle cell
103
what happens at the neuromuscular junction
there is one fibre per endplate
- the impulse arrives and triggers the ca+ influx
- the neurotransmitter acetylcholine (nAChr) then binds to the nicotinic cholinergic receptors concentrated on the motor end plate
- this generates the end plate potential which is the muscle action potentials and this increases the ca+ concentration( for the contraction of muscles )
104
what are features of the motor end plate
- made up of junctional folds, thickened muscle membrane
- the synaptic cleft is similar to regular synapses
- receptors are concentrated on the tops of the folds
- acetylcholine is cleaved by acetylcholinesterase into acetate and choline which is transported back to the presynaptic membrane
105
what are the different types of channels on the synapse
- acetylcholine na+ channel (causes influx)
- ca2+ VGC on the sarcolemma (influx)
- ca2+ channels on the sarcoplasmic reticulum (influx)
106
what happens with the muscle action potential
- ryanodine receptor activated by voltage sensitive DHP receptor
- release of ca2+ from the sarcoplasmic reticulum
- influx of ca+ which binds to troponin and triggers myosin contraction
107
what happens to the action potential in myasthenia gravis
some of the action potentials does not reach the threshold potential so no muscle contraction occurs and this leads to fatigue
108
features of nerve endings in smooth and cardiac muscle
- no neuromuscular junctions
- no recognizable end plates or other postsynaptic specializations
- the branches of neurons have enlargements (varicosities) containing synaptic vesicles
- transmitter released at each varicosity
- one neuron innervate many effector cells
109
what is the acetylcholine receptor coupled to
passive transport
110
how are neurotransmitters secreted
regulated secretory pathway
