Cells

Question 1

Address for nuclear proteins

Answer 1

Nuclear localisation signal. Importin is analogous to SRP.

Question 2

Address for mitochondrial proteins

Answer 2

Mitochondrial import sequence in N-terminus of protein. Imported via translocases.

Question 3

Address label for peroxisomes.

Answer 3

C-terminal peptide.

Question 4

Define ‘Tissue’

Answer 4

Group of cells working together to carry out a common function. Parenchyme=working tissue. Stroma=scaffold and nutrition.

Question 5

Describe ‘fixation’ of tissues.

Answer 5

Can be either by freezing (-80oC) by dry ice or liquid nitrogen or chemical fixation, aldehyde based commonly.

Question 6

What are the 5 classes of macromolecules that make up the ECM?

Answer 6

Collagens, Elastin, Proteoglycans, Hyaluronon (a glycosaminoglycan) and other glycoproteins.

Question 7

Give details about Elastin

Answer 7

Structural protein arranged as fibres. Abundant in skin, lung and blood vessels where it provides stretch and elastic recoil. Assembly into functional fibres requires the presence of a structural glycoprotein- fibrillin. It is synthesized as tropoelastin and undergoes hydroxylation. Uses a fibrin scaffold and cross-linked fibres to assemble.

Question 8

What is ground substance?

Answer 8

An amorphous, colourless, gelatinous material that fills the spaces between fibres and cells. Consists of large molecules called glycosaminoglycans which link together (with a core protein) to form even larger molecules called proteoglycans. It is very good at absorbing water (90% of ECM is water). It is resistant to compressive forces.

Question 9

What are glycosaminoglycans?

Answer 9

Chains of repeating disaccharide units. The carbohydrate component of proteoglycans. Examples of GAGs, hyaluronic acid, keratan sulphate, heparan sulphate.

Question 10

What is aggrecan?

Answer 10

A type of proteoglycan with chondroitin sulphate and keratan sulphate as the GAGs. Aggregan interacts strongly with collagen type II in the ECM of cartilage, contributing to the development and tensile strength of this connective tissue.

Question 11

What is fibrillin?

Answer 11

A structural glycoprotein that controls deposition and orientation of elastin.

Question 12

What is fibronectin?

Answer 12

A structural glycoprotein that has a linker role in the BM. Organised ECM and participates in cell attachment to the BM.

Question 13

What is laminin?

Answer 13

A structural glycoprotein that is the primary organiser of the BM layer.

Question 14

What are the layers of the basement membrane/lamina and what is it made of?

Answer 14

-Lamina lucida
-Lamina densa
-Lamina fibroreticularis
Composed of collagen IV, laminin, perlecan (heparan sulphate proteglycan), entactin and fibronectin.

Question 15

What are the functions of the BM?

Answer 15

Support, binding to underlying connective tissue, mediates signals between cells and connective tissue, determines cell polarity, permits flow of nutrients (permeability), path for cell migration, barrier to downward growth.

Question 16

What is Goodpastures syndrome?

Answer 16

When autoantibodies to collagen IV destroy the BM in glomerulus and lung.

Question 17

Where would you find hyaline cartilage?

Answer 17

Nasal septum, tracheal rings, articular surfaces, epiphyseal growth plate.

Question 18

Where would you find fibrocartilage?

Answer 18

IV discs, sternoclavicular joint, pubic symphysis.

Question 19

Where would you find elastic cartilage?

Answer 19

External ear, epiglottis, auditory tube.

Question 20

What is Marfan syndrome?

Answer 20

A genetic disorder of the ECM. Mutation in the gene that codes for Fibrillin-1. Leads to skeletal, ocular and cardiovascular deformities.

Question 21

What is supravalvular aortic stenosis?

Answer 21

A genetic condition where there is a mutation in the elastin gene. Leads to arterial defects.

Question 22

What causes Ehlers-Danlos syndrome?

Answer 22

Mutation in collagen genes that lead to joint and skin abnormalities.

Question 23

What does mutations of Perlecan cause?

Answer 23

Silverman-Handmaker tye of dyssegmental dysplasia (DDSH): neonatal lethal dwarfism.

Question 24

What do mutations in keratan sulphate cause?

Answer 24

Macular corneal dystrophy:corneal transparency.

Question 25

What is a hormone response element (HRE)?

Answer 25

A short sequence of DNA within the promoter of a gene that is able to bind to a specific hormone receptor complex and therefore regulate transcription.

Question 26

What are ‘second messengers’?

Answer 26

Small molecules (eg. IP3, cAMP, DAG) that transduce
signal from cell surface to effector proteins that produce the cell’s response. Amplification.

Question 27

What do phosphodiesterases do?

Answer 27

Break down cAMP.

Question 28

In which organelle does glycosylation principally occur?

Answer 28

Golgi.

Question 29

In a typical epithelial cell, which cell junction is usually found closest to the apical surface?

Answer 29

Tight junction is usually found closest to the apical surface and is involved in maintaining the polarity of the cell (ie separating the apical surface from the basolateral domain) as well as paracellular permeability.

Question 30

A 20 year-old student spends the day in the sun. Although she initially goes a little red, in the next few days she starts to develop a suntan.

Which of the following cell types is responsible for her eventual change in skin colour?

Answer 30

Melanocytes, these produce melanin and transfer the pigment to surrounding keratinocytes, via secretory organelles named melanosomes.

Question 31

Which of the following cell junctions would be loosened at the basement membrane?

Answer 31

Hemidesmosomes form junctions between the intermediate filament cytoskeleton and the extracellular substratum.

Question 32

A 7 year-old boy falls off his scooter and gets a superficial graze on his arm. Although it looks red, it doesn’t bleed and it heals in a few days.
Which of the following layers of skin is most active in the healing of this wound?

Answer 32

Stratum basale. Because there is no bleeding, there is presumed to be no damage to the dermis and hence only epidermal cells are involved in the healing process. Cells of the stratum basale are capable of mitotic division and they differentiate to replenish the more superficial layers (S.spinosum, etc).