Topics 3,4,5 - Movement into Cells Flashcards
Learning Objectives
1.Explain how cell membranes create compartmentisation which regulate the flow of substances in and out of the cell
2.Descibe the passive diffusion of water across semi-permiable membranes and the role of aquaporins.
3.Describe how the cell uses the Na-K ATPase to create elecrochemical gradients
4.Explain how larger molecules and particles get in and out of cells
5.Descibe the endocrine system and hormones
6.Explain how hormones allow distant cells to communicate
7.Explain the roles of messengers and receptors in cell communication
8.Describe the difference between lipid-soluble and water soluble hormones
9.Explain the basic mechanism of steroid hormone responses
10.Explain the differences between first and second messengers, with cAMP as an example
11.Explain negative and positive feedback loops w/ examples
12.Describe an example of homeostasis
13.Describe how sensors and feedback systems operate to maintain homeostasis in negative feedback loops
14.Explain the basis of how the body regulates extracellular fluid osmolarity
15.Explain how oxytocin and ADH work
Cells
Surrounded by semi-permiable plasma membranes
- Made up of a phospholipid bilayer
- Hydpophilic Phospahte Head
- Phydrophobic lipid tail
Impermiable to most essential molecules and ions
Movement of molecules
Diffusion:
- Molecules become equally distributed with random movement
Osmosis:
- Bulk flow of water through a semi-permiable membrane into another aqueous compartment containing solute at a higher concentration
- Water “wants” to be at equilibrium
Tonicity
Osmotic pressure gradient
Isotonic
External solution that has the same solute concentration compared to the body of fluid
Hypertonic
External solution that has a high solute concentration and low H2O concentration (Gains water)
Hypotonic
External solution has a lower concentration of solute and higher H2O (loses water)
Ion Transport
Potassium pump channels in the cell membrane open w/ help of proteins allowing for K+ and Na+ ions to pass through
Intergral Membrane Proteins
Types and their functiosn
Allow for larger molecules/ particles to get in and out of the cell
Channel:
- Facilitated diffusion, allowing ions to flow down concentration gradient (no ATP required)
Transporters:
- Facilitated diffusion OR Active Transport
- Active Transport requires ATP
Aquaporins
Special water channels to allow for large amounts of water into the cell
- Kidney and gut to allow maximal function capacity
Active Vs Passive transport
Active:
- Movement against concentration gradient using ATP
Passive:
- Movement down concentration gradient via Simple diffusion or Facilitated diffusion (no ATP)
Ion Channels
Conduct charges by creating an electrochemical gradient
A membrane potential is formed when one side of the membrane has a different charge to the other.
Sodium Potassium Pump
(Na-K ATPase)
SOPI
- 3 Na+ ions bind to intracellular sites on the pump
- A phosphate group is transferred to the pump via hydrolysis of ATP
- The pump undergoes a conformational change, translocating the 3 Na+ across the membrane out of the cell
- two K+ binding sites on the extracellular surface of the pump are then opened, 2 K+ ions bind to the sites
- The phosphate group is released, causing the pump to return to its original shape
- This translocates the potassium across the membrane into the cell
Consequences of Na-K ATPase action
A membrane potential is created though 2K+ entering and 3Na+ leaving the cell, creating a negative charge.
Na-K ATPase contribute to Nerve action potentials by building a negative membrane potential threshold.
Facilitated diffusion
Transporters allow for larger molecules that are unable to freely cross the bilayer, to get into the cell
- Channel and Carrier
Carrier proteins
Integral glycoprotein that regulates the momevement of nutrients accross the membrane down concentration gradient
- Undergo conformational change to allow solute accross the membrane
- Slower rate of transportation
Channel Proteins
Integral glycoproteins containing a pore via which ions may freely pass across the membrane
- Ion selective and may be gated to regulate flow
- Moves along/ down concentration gradient
- Fast rate of transportation
Endocytosis
Cell ‘engulfing’ small bulks of substances without it passing through the membrane
- Pinocytes and Phagocytes
Pinocytosis = solid substances
Phagocytosis = liquid substances
Exocytosis
Large substances OR bulk transport of substances exit the cell without passing through the membrane
- Vessicles from golgi complex fuse w/ plasma membrane to expell its contents
- Replaces lost portions of the membrane that are used in endocytosis, maintaining its membrane size
Homeostasis
Organism or cells maintaining their internal environment w/ tolerance limits
- Governed by negative feedback loops
Feedback loops
Negative:
- A response is detected by a receptor, an effetcor is then activated to induce a reversed change to the response that is detected
- Eg. Thermoregulation, Blood sugar, Osmoregulation
Positive:
- A response is detected by a recepter, an effector is then activated and amplifies the initial stimili to move further away from its starting point.
- Eg. Contractions during child birth, Blood clotting, Milk Secretion
Endocrine system
A slower chemical based messenging system to help maintain homeostasis
- A system of ductless glands/ organs that release chimicals (hormones) into the blood stream to regulate body functions
- Has a more prolongued response compared to nervous system
Hormones
Chemical messenger transported via blood stream to act on distant or neighbouring target cells
- Hormones are specific and only activate cells/ tissues that have the appropriate taget receptor
Endocrine gland
Ductless gland that produces an internal secretion discharged into the blood or lymph and circulated to all parts of the body
Endocrine
An internal secretion that pertains a gland that secretes into the blood stream
Exocrine
External secretion via ducts to the epithelial surface
Functions of Hormones
Metabolism:
- Thyroid stimulating hormone (TSH), activates thyroxin
Adult development:
- Leutinising hormone (LH) starts ovulation
- Follicle stimulating hormone (FSH) maintains follicle growth
Reproduction:
- LH and FSH control menstration
Growth:
- Growth Hormone-Releasing hormone (GHRH) triggers body growth of limbs
Equilibrium
- Anti-Duiretic Hormone (ADH) released when body fluids are hypertonic to trigger reabsorbtion of water
Insulin
- Signalling molecule (Ligand)
- Binds to a receptor on the cell membrane
Steps of Insulin binding to the receptor
- Insulin binds to the G-protein receptor on the cell membrane with a high affinity
- The receptor complex then actives second messengers into the cytoplasm to initiate cellular activity
- Second messengers then relay the recieved signals
- With signal transduction, second messengers initiate cellular activity. The active cells are inititated in the nucleus, leading the the cellular response.
Water solube hormones
Peptide hormones cannot cross the membrane
- Require transmembrane proteins
Signal amplification
When a receptor is activated, proteins OR secend messengers inside the cells are phosphorylated in cascades by kinase leading to signal transduction
Phosphorylation
The addition of a phosphoryl group (PO3) to a molecule
- ATP into ADP
Since phoshate groups are highly -ve in charge, phosphorylation of a protein alters its charge and can alter its conformation and functional activity.
Second messengers
- Molecules whose presence is a signal
- Acts as amplifiers
- Synthesised or released from storage
- Act as intrecelluar ligands
- Have low amounts in resting state
- Regulate synthesis
- Regulate deconstruction
- Act tghrough other protiens
** Cyclic AMP (cAMP)
Calcium**
Cyclic AMP (cAMP)
- Comes from ATP
Ezyme called Adenyly cyclase converts ATP into cAMP
When signalling of second messengers is finished, phosphodiesterase breakes it back down
- Acts as a ligand for kinase which phosphorylate the proteins
GPCR signalling
- “G Protein Coupled receptors”
G proteins bind GTP (Guanosine Triphosphate)
- Epinephrine binds to G Protein Coupled receptor (GCPR)
- G protein in the membrane is then activated and diffuses across the membrane to adenylyl cyclase
- Once at Adenylyl cyclase, cAMP is created from ATP
- cAMP acts as a second messenger and acts on Protein Kinase A to start the signalling responses
- The signal response can be continued for amplification of a cellular response.
Calcium
Ca2+
- Very low concentration inside the cell
- Has profound effects on protein activity, Interactions, conformation
- Regulated with Ca2+ pumps
- Stored in the ER, Nucleus and mitochondria.
- The Ca2+ pumps keep the cytocol low in Ca2+ concentration
Calcium as a second messenger
- When Membrane receptors are activated, Ca2+ floods into the cell very fast
- This changes cellular actions at all levels (Eg. Neurotransmitters, Voltage agted calcium channels)
Steroid receptors
- Lipid based (Lipophilic)
- Can entre cell without problems
- Transported through blood stream to cells of various target organs. (Uterus, vagina mammary glands, skin, brain)
- Causes growth and is responsible for endometrial growth and menstration involvement.
Process of steroid receptors
- Steroid hormone entres the cell and finds receptor in the cytoplasm
- Forms a receptor-hormone complex (a protein)
- Receptor hormone complex is then translocated into the nucleus
- Binding directly yo DNA and initiates transcription for gene expression
Pituitary gland role
- In the brain
- Endocrine gland working with the hypothalamus
- Contains posterior and anterior lobes
Anterior:
- Releases GH, FSH, LH, TSH
Posterior:
- Releases ADH, Prolactin, Oxytocin
Oxytocin
Released by posterior pituitary gland
- Promotes uterine contractions during child birth
- Promotes breast milk ejections
Works via positive feedback loops
Anti-Duiretic Hormone (ADH)
Released by Posterior Pituitary gland
Released in Respose to:
- Rise in blood osmolarity
- Fall in blood pressure
- Fall in blood volume
- Prevents water loss through the kidneys (prevent duiresis)
- Uses aquaporins in the kidney.
List the Endocrine System
Brain:
- Pineal gland (melatonin)
- Hypothalamus (Release into pituitary)
- Pituitary gland (FSH, LH, ADH)
Thymus
Pancreas (Insulin, glucagon)
Thyroid (Thyroxin)
Adrenal gland (epinephrin, cortisol)
Ovaries/ Testes (Estrogen, Propgesterone/ Testosterone)
