Cell Signalling 5 Flashcards
(26 cards)
Where are nuclear receptors found ?
- Nucleus
- Cytoplasm. After ligand binding them will translocate to the nucleus.
What do nuclear receptors bind? How do they exert their effect ?
Lipid soluble molecules such as steroid hormones or small molecules that can pass through the lipid bilayer.
Exert effects by affecting gene transcription.
Describe the structure of nuclear receptors
- A ligand binding domain
- A DNA binding domain- binds to response elements
- N terminal domain- can be modified by other molecules to enhance transcriptional abilities
Explain mediation of gene transcription by cortisol
- Cortisol is produced in the adrenal glands in response to stress
- Passes through lipid bilayer and binds to its cytoplasmic nuclear receptor
- Ligand-bound receptor translocates to nucleus
- Binds to regulatory response elements in target gene to drive gene transcription
What is oestradiol ?
An oestrogen that is synthesised from testosterone by an enzyme called aromatase.
It is hydrophobic so can cross the nuclear membrane.
Explain how breast cancer occurs
- Oestradiol binds to oestrogen receptors in the nucleus
- The receptor dimerises, associate with co-activators and form a complex which acts as a transcription factor
- The transcription factor activates oestrogen response elements which alters transcription and increases cell proliferation
What are plasmodesmata ?
Facilitate juxtacrine
They are comprised of cytoplasmic channels that link adjacent cells.
They aid in electrical signalling between plant cells
Why do we need electrical signalling in plants ?
Allows relatively rapid long-distance communication eg. In response to stress/damage
Food capture in carnivorous plants
Describe the electrical signalling in Venus flytrap
Stimulation of sensory trigger hairs activated mechano-sensitive ion channels.
This leads to depolarisation of membrane and generation of action potential.
This changes turgor pressure in hinge cells, causing closure of leaf lobes.
What kinase do plants have that animals don’t ?
Histidine kinase
What is the natural auxin in plants ?
Indoleacetic acid (IAA)
Where are auxins produced?
- Seed embryo
- Meristems of apical buds
- Young leaves
They only flow down the plant
What are the functions of auxins ?
- Stem elongation
- Root growth
- Branching
- Fruit development
- Apical dominance
5
Describe the photropic response of shoots
It is mediated by the blue-light photoreceptor, phototropin.
Auxin moves to the shaded side, which induces cell elongation, so the shoot bends towards the light.
How does auxin affect gene transcription?
- Auxin binds to its nuclear receptors which are ubiquitin ligases
- Binding promotes ubiquitinylation and degration of repressor protein
- Gene transcription is activated
What is ethylene ?
It is a plant hormone that is a gas.
It can pass through cell walls or diffuse through air.
What are the functions of ethylene?
- Fruit ripening
- Leaf abscission
Describe the ethylene response
- Ethylene receptors are found in the membrane of the ER and Golgi
- In the absence of ethylene, the receptor activates a kinase, which promotes the destruction of the transcription regulator
What does deactivation of the ethylene receptor allow ?
Transcription of ethylene sensitive genes
What are the 2 main classes of photoreceptors in plants ?
- Blue-light receptors- cell surface receptors
Contain either cryptochromes, phototropin or zeaxanthin as photopigments - Photochromes (red and far-red light)
What is the role of phototropin ?
To mediate phototropism by inducing signalling which influences auxin redistribution
What is the role of cryptochromes ?
Influence de-etiolation (growth and changes)
What is the role of phytochromes ?
Regulate photoperiodism- response of plants to the period of night and day
Red light (day)
Far-red light (night)
