biology

High Affinity K+ transporter HAK5

High Affinity K+ transporter HAK5 is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand High Affinity K+ transporter HAK5 rather than just read about it. In short: High Affinity K+ transporter HAK5 is a transport protein found on the cell surface membrane of plants under conditions of potassium deprivation. It is believed to act as a symporter for protons and the potassium ion, K+.

Key takeaways

High Affinity K+ transporter HAK5 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect High Affinity K+ transporter HAK5 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of High Affinity K+ transporter HAK5 from memory before moving on to harder problems.

Reference excerpt

High Affinity K+ transporter HAK5 is a transport protein found on the cell surface membrane of plants under conditions of potassium deprivation. It is believed to act as a symporter for protons and the potassium ion, K+. Firstly discovered in barley, receiving the name of HvHAK1, it was soon after identified in the model plant Arabidopsis thaliana and named HAK5. These transporters belongs to the subgroup I of the KT-HAK-KUP family of plant proteins with obvious homology with both bacterial and fungal transport systems, which experienced a major diversification following land conquest. KT-HAK-KUP transporters are one of four different types of K+ transporter within the cell, but are unique as they do not have a putative pore forming domain like the other three; Shaker channels, KCO channels, HKT transporters. It is activated when the plant is situated in low soil with low potassium concentration, and has been shown to be located in higher concentration in the epidermis and vasculature of K+ deprived plants. By turning on, it increases the plants affinity (uptake) of potassium. Potassium plays a vital role in the plants growth, reproduction, immunity, ion homeostasis, and osmosis, which ensures the plants survival. It is the highest cationic molecule within the plant, accounting for 10% of the plants dry weight, which makes its uptake into the plant important. Each plant species has its own HAK5 transporter that is specific to that species and has different levels of affinity to K+. To operate and activate the HAK5 transporter, the external concentration of K+ must be lower than 10μM and up to 200μM. In Arabidopsis plants, when external potassium concentration is lower than 10μM, it is only HAK5 that is involved with the uptake of K+, then between 10 and 200μM both HAK5 and AKT1 are involved with the uptake of K+. HAK5 is coupled with CBL9/CIPK23 kinase's although the mechanism behind this has not yet been understood.

Interaction The High Affinity K+ transporter interacts with the following proteins

ILK1 CBL9- CIPK23 AKT1

Activation CIPK23 acts to phosphorylate HAK5, the phosphorylation is what activates the HAK5 to take up K+. HAK5 is positively controlled by CIPK23- CBL1-9 complexes, Ca2+ binds with CBL1-9, which then combines with CIPK23 to form a CIPK23/CBL complex, the complex then initiates the up-regulation of the HAK5 protein transporter by phosphorylating the N- terminus of the HAK5. This mechanism acts in a similar way in which ATK1,(another K+ transporter) is activated, however the only difference is that ATK1 only interacts with CBL1 and CBL9, whereas HAK5 interacts with CBL1, CBL8, CBL9 and CBL10.

Functions High Affinity K+ transporter HAK5 effects multiple functions of the plant when in low potassium concentrations these are;

Osmosis Ion Homeostasis Immune Response Growth

Osmosis Higher levels of potassium in the roots creates a greater amount of photosynthesis in the leaves by helping to control osmosis occurring throughout the cells. By controlling potassium, the HAK5 potassium transporter plays this important role in osmosis, and creates large influxes of water molecules to the plant to ensure its survival. By increasing the affinity of potassium uptake within the plant, it lowers the concentration of water within the cell. This increases the concentration of solute outside, creating a hypotonic solute. The water will then move into the plant cell via osmosis.

Ion homeostasis A cell membrane consists of many transport proteins that allow for ion transport, as ions can not simply pass through the gradient due to their charge. High Affinity K+ transporter HAK5, is important for the regulation of K+ ions within the cell. When there is a lack of K+, the HAK5 transporter is activated to uptake K+. This occurs when there is high salinity within the soil, which often happens within the crop industry. If the soil has a high salinity content, this means Na+ from NaCl competes with K+ for uptake because they are similar ions and use the same transporters. However, K+ accounts for the activation of over 50 enzymes, which Na+ cannot be a substitute. With HAK5 transporters, this competition is lowered, as there is a specific transporter for K+ that insures its uptake. The transporter for K+ ensures that the K+ and Na+ maintain homeostasis in the plant. K+ is required for environmental changes like putting the plant into a higher salinity situation. K+ ensures plants are able to adapt to these changes. The only way in which they are able to obtain this K+ whilst in high salinity conditions is through HAK5 transporters regulating the amount because it is only turned on when there is a low concentration of K+ in the soil.

… excerpt ends here. Continue reading the full article.

Illustrations

High Affinity K+ transporter HAK5: This image shows how the HAK5 is activated only when the plant is in a low potassium environment, which then increases the cells affinity for potassium ions.This is the protein sequence of the High Affinity K+ transporter, HAK5. — This image shows how the HAK5 is activated only when the plant is in a low potassium environment, which then increases the cells affinity for potassium ions.This is the protein sequence of the High Affinity K+ transporter, HAK5.

Worked examples

Example 1 — a first encounter with High Affinity K+ transporter HAK5

Start with the simplest possible case. Write down what High Affinity K+ transporter HAK5 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to High Affinity K+ transporter HAK5 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about High Affinity K+ transporter HAK5 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of High Affinity K+ transporter HAK5

In research: High Affinity K+ transporter HAK5 appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses High Affinity K+ transporter HAK5 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: High Affinity K+ transporter HAK5 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Transport proteins, so understanding it makes those chapters shorter.
In everyday life: Look for High Affinity K+ transporter HAK5 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study High Affinity K+ transporter HAK5 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what High Affinity K+ transporter HAK5 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain High Affinity K+ transporter HAK5 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is High Affinity K+ transporter HAK5 in simple terms?

Why does High Affinity K+ transporter HAK5 matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study High Affinity K+ transporter HAK5?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on High Affinity K+ transporter HAK5.