Vitamins and Their Functions
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Questions and Answers

What is a primary characteristic of vitamins?

  • Vitamins can be synthesized in sufficient quantities by the organism.
  • Vitamins are essential micronutrients required in small quantities. (correct)
  • Vitamins are inorganic molecules.
  • Vitamins provide all necessary calories for energy.

Which of the following statements about vitamin deficiencies is true?

  • Micronutrient synthesis in the body can eliminate vitamin deficiencies.
  • Vitamin deficiencies are only caused by dietary shortages.
  • Vitamin deficiencies do not occur in older people.
  • Medical treatments such as antibiotics can lead to vitamin deficiencies. (correct)

How are vitamins classified?

  • According to their mechanical properties.
  • Based on their caloric content.
  • By their solubility and biological function. (correct)
  • Into primary and secondary categories.

Which of the following vitamins is NOT fat-soluble?

<p>Vitamin B12 (B)</p> Signup and view all the answers

What can result from malnutrition or certain medical conditions?

<p>Hypovitaminosis or avitaminosis. (D)</p> Signup and view all the answers

Which vitamins can typically be stored in the body?

<p>Vitamin A, Vitamin D, Vitamin E, and Vitamin K (A)</p> Signup and view all the answers

What happens when there is an overdose of certain vitamins?

<p>Fat-soluble vitamins A and D can lead to hypervitaminosis. (D)</p> Signup and view all the answers

How are the daily vitamin requirements of an individual influenced?

<p>By variables like age, sex, and physiological conditions. (D)</p> Signup and view all the answers

What role does the enzyme activated by the G protein transducin play in the visual process?

<p>It breaks down the second messenger cGMP. (B)</p> Signup and view all the answers

Which vitamin is a precursor of the hormone retinoic acid?

<p>Vitamin A (D)</p> Signup and view all the answers

Which type of photoreceptor cell is responsible for vision in low light conditions?

<p>Rods (B)</p> Signup and view all the answers

What is the primary function of retinal in the human body?

<p>Functions in visual processes (A)</p> Signup and view all the answers

What effect does Vitamin A deficiency have on vision?

<p>Causes night blindness and visual impairment (D)</p> Signup and view all the answers

What is the maximum wavelength of light absorption for rhodopsin?

<p>500 nm (D)</p> Signup and view all the answers

Which vitamin is known to vary in requirement due to physiological conditions such as pregnancy?

<p>Vitamin B-9 (D)</p> Signup and view all the answers

Which statement about the allosteric conformational change in rhodopsin after photon absorption is true?

<p>It allows rhodopsin to bind and activate transducin. (A)</p> Signup and view all the answers

Which vitamin is a fat-soluble vitamin found in meat-containing diets?

<p>Vitamin A (B)</p> Signup and view all the answers

What role does retinal play in the structure of rhodopsin?

<p>It is bound as an aldimine to the ε-amino group of a lysine residue. (D)</p> Signup and view all the answers

Which of the following vitamins is exclusively classified as a water-soluble vitamin?

<p>Vitamin B-7 (C)</p> Signup and view all the answers

Which vitamin can be synthesized from β-carotene?

<p>Vitamin A (B)</p> Signup and view all the answers

What initiates the signal cascade in rod cells when light is detected?

<p>Activation of rhodopsin by light (C)</p> Signup and view all the answers

What is a potential consequence of hyperpolarization of light-sensitive cells in the retina?

<p>Inhibition of visual signaling (C)</p> Signup and view all the answers

What role does retinoic acid play in cellular processes?

<p>Influences transcription of genes (A)</p> Signup and view all the answers

Which vitamin is associated with the coenzymes involved in metabolic processes?

<p>Vitamin B-3 (D)</p> Signup and view all the answers

What are some consequences of vitamin A toxicity?

<p>Cessation of menstruation and headaches (D)</p> Signup and view all the answers

Which hormone is a precursor to the active form of vitamin D?

<p>Cholecalciferol (D)</p> Signup and view all the answers

Which hormone primarily acts to decrease blood calcium levels?

<p>Calcitonin (A)</p> Signup and view all the answers

What is the primary role of parathyroid hormone (PTH)?

<p>To stimulate calcitriol production and increase blood calcium levels (A)</p> Signup and view all the answers

What deficiency can lead to osteomalacia in adults?

<p>Vitamin D deficiency (C)</p> Signup and view all the answers

What is the role of cGMP in rod cells during dark conditions?

<p>It maintains the ion channels in an open state. (B)</p> Signup and view all the answers

Which event occurs first when light activates rod cells?

<p>Activation of cGMP phosphodiesterase by the GTP-bound α_subunit. (D)</p> Signup and view all the answers

Which substance regulates calcium metabolism in healthy adults?

<p>Calcitriol and parathyroid hormone together with calcitonin (A)</p> Signup and view all the answers

How much calcium is typically absorbed daily in healthy adults?

<p>Around 1g (B)</p> Signup and view all the answers

What occurs after the hydrolysis of cGMP in rod cells?

<p>Closure of ion channels due to cGMP dissociation. (A)</p> Signup and view all the answers

What happens during the recovery phase of rod cells after exposure to light?

<p>cGMP levels are restored, reopening cation channels. (C)</p> Signup and view all the answers

What is a primary food source high in calcium?

<p>Cheese and milk products (A)</p> Signup and view all the answers

What is one consequence of vitamin A deficiency?

<p>Development of night blindness. (A)</p> Signup and view all the answers

Which of the following mechanisms restores cGMP levels in rod cells after light exposure?

<p>Activation of guanylate cyclase by increased Ca2+. (C)</p> Signup and view all the answers

What is the function of the isomerase in the visual signal cascade?

<p>It converts all-trans-retinal back to 11-cis-retinal. (C)</p> Signup and view all the answers

What triggers the hyperpolarization of rod cells in response to light?

<p>Closure of sodium and calcium ion channels. (A)</p> Signup and view all the answers

What is the primary function of vitamin E in biological membranes?

<p>Acts as an antioxidant (C)</p> Signup and view all the answers

Which of the following is a consequence of vitamin E deficiency?

<p>Axonal degeneration (A)</p> Signup and view all the answers

How does vitamin E prevent lipid peroxidation?

<p>By donating an H atom to free radicals (A)</p> Signup and view all the answers

Which types of foods are good sources of vitamin E?

<p>Vegetable oils and nuts (B)</p> Signup and view all the answers

What type of chemical structure is characteristic of vitamin E?

<p>A chromane ring (C)</p> Signup and view all the answers

What is a common feature of reactive oxygen species (ROS)?

<p>They contain unpaired electrons. (B)</p> Signup and view all the answers

Which radical is produced when dioxygen gains an extra electron?

<p>Superoxide radical (A)</p> Signup and view all the answers

What impact do oxidized LDL particles have on health?

<p>They are linked to atherogenesis and coronary artery disease. (B)</p> Signup and view all the answers

Flashcards

Avitaminosis

Avitaminosis occurs when your body lacks a crucial vitamin, which can cause health issues. These issues might impact the skin, blood cells, or the nervous system.

Hypovitaminosis

Hypovitaminosis refers to having a lower level of a specific vitamin in your body, which might not lead to significant health problems immediately, but if left unaddressed can lead to deficiency issues.

Dietary Deficiency

A dietary deficiency can be caused by a lack of a nutrient, often due to an unbalanced diet or a condition that prevents the body from absorbing nutrients effectively.

Vitamins

Vitamins are essential organic molecules your body needs in small amounts for various metabolic processes. Your body can't always produce enough of them, so you must obtain them through your diet.

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Essential Nutrients

Essential nutrients are substances that the body requires for optimal function but cannot create on its own, so they must be obtained through the diet. Vitamins are a good example of this.

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Fat-soluble Vitamins

Fat-soluble vitamins are absorbed and stored in fat tissue. This means they're not readily excreted from the body, making it more likely to over-consume them. Examples include vitamins A, D, E, and K.

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Water-soluble Vitamins

Water-soluble vitamins dissolve in water and are usually excreted through urine. This means your body needs a regular intake of them, as they're not stored for long. Examples include B vitamins and vitamin C.

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Vitamin Requirements

Vitamin requirements are the amount of each vitamin your body needs daily. These requirements depend on factors like age, sex, health status, and even your physical activity levels.

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What are some examples of water-soluble vitamins?

These vitamins are important for cell function, growth, and development, as well as energy production and nerve function. Examples include B1 (thiamine), B2 (riboflavin), B3 (niacin), and B12 (cyanocobalamin).

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What are some examples of fat-soluble vitamins?

These vitamins are key to vision, bone health, and immune function. Examples include Vitamins A, D, E, and K.

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What is Vitamin A?

Also known as retinol, the parent substance of other retinoids like retinal and retinoic acid. It is important for vision.

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What is retinal?

A pigment found in the chromoprotein rhodopsin, it is crucial for visual processes in the eyes and functions as both a visual pigment and a hormone.

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What is retinoic acid?

A form of Vitamin A that acts a differentiation factor in cell growth and development. It influences gene transcription in the nucleus.

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What is provitamin A?

Also known as β-carotene, a precursor of Vitamin A. Can be found in fruits and vegetables, especially carrots. It is converted into Vitamin A in the body.

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Rhodopsin

A light-sensitive pigment found in rod cells of the eye. It is responsible for detecting low levels of light.

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Rod Cell

A type of photoreceptor cell in the retina that is sensitive to dim light, enabling night vision.

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Cone Cell

A type of photoreceptor cell in the retina that is responsible for color vision in bright light.

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Neurotransmitter

A molecule that transmits signals between cells. It acts as a messenger, relaying information across synapses.

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Synapse

A specialized junction between two neurons, where a chemical signal is transmitted from one neuron to the next.

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Second Messenger

A chemical messenger that triggers a biological response in the cell. It reacts to external stimuli, such as light.

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Retinal

A light-absorbing molecule that changes shape when it absorbs a photon of light, triggering a cascade of events in vision.

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Transducin

A protein that activates a signal cascade when bound by rhodopsin*, leading to reduced neurotransmitter release.

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cGMP (Cyclic GMP)

A cyclic nucleotide that is essential for keeping the ion channels in rod cells open, allowing cations to flow in and depolarize the cell.

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cGMP phosphodiesterase

An enzyme that breaks down cGMP, leading to the closure of ion channels and hyperpolarization of the rod cell.

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Photoreceptor Regeneration

The process by which a rod cell returns to its resting state after being exposed to light, enabling it to respond to further light stimuli.

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Night Blindness

The condition caused by vitamin A deficiency, leading to night blindness due to impaired rod cell function.

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Metaplasia

The change of one cell type to another, often occurring in the cornea due to vitamin A deficiency.

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Isomerization

The transfer of all-trans retinal to the 11-cis form, a step in the regeneration of rhodopsin.

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What is Vitamin E's main function in the body?

A crucial component in biological membranes, it acts as an antioxidant, protecting lipids from damage by reactive oxygen species (ROS).

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How does Vitamin E protect cells from damage?

Vitamin E donates a hydrogen atom to free radicals, neutralizing their damaging effects.

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How does Vitamin E potentially help cardiovascular health?

It prevents the oxidation of LDL particles, which are strongly linked to atherosclerosis and heart disease.

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What is a reactive oxygen species (ROS)?

A chemical that can harm cells by reacting with their components, often created during normal metabolic processes.

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Where can Vitamin E be found?

Wheat germ is an excellent source of Vitamin E.

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What happens if you don't get enough Vitamin E?

A deficiency in Vitamin E can lead to red blood cell fragility, nerve damage, and even vision problems.

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How does Vitamin E affect cell membranes?

Vitamin E plays a vital role in maintaining the fluidity of cell membranes.

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How is Vitamin E absorbed in the body?

Vitamin E is a fat-soluble vitamin, meaning it needs fat to be absorbed and stored in the body.

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What is Vitamin D deficiency disorder?

A condition that occurs when the body doesn't absorb enough calcium, leading to weakened bones. Often seen in children (rickets) and adults (osteomalacia).

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What is the role of Calcitriol?

A hormone that helps regulate calcium levels in the blood, primarily by increasing calcium absorption in the intestines and kidneys. It also promotes calcium release from bones.

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What does Parathyroid Hormone (PTH) do?

A hormone that helps regulate calcium levels in the blood by promoting calcium release from bones and decreasing calcium excretion by the kidneys.

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What is the role of Calcitonin?

A hormone that lowers calcium levels in the blood by inhibiting calcium release from bones and increasing calcium excretion in the kidneys.

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How does Vitamin D synthesis occur in the body?

This process involves the conversion of 7-dehydrocholesterol in the skin into Vitamin D using ultraviolet (UV) light.

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What happens when there is excess Vitamin A?

Excessively high levels of vitamin A can lead to various health problems.

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What is Calcium Homeostasis?

This refers to the regulation of calcium levels in the blood. This involves a balance between absorption, excretion, and bone metabolism.

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Which food group is renowned for being high in Calcium?

Milk products like cheese are particularly rich in this mineral.

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Study Notes

Human Metabolism - Biochemistry

  • ATP (Adenosine Triphosphate): A crucial energy molecule in the human body. It carries energy in its phosphate bonds.

  • Mitochondria: Cellular structures responsible for ATP production. They have inner and outer membranes. The inner membrane is critical for oxidative phosphorylation, a process that generates ATP.

Vitamins

  • Vitamins are organic micronutrients, essential for proper metabolic function. Unlike other nutrients, the body cannot synthesize them in sufficient quantities. They must be obtained through the diet.

  • Types of Vitamins: Vitamins are categorized as either water-soluble or fat-soluble. Water-soluble vitamins, like vitamin C and B vitamins, are generally not stored in the body and need to be consumed regularly. Fat-soluble vitamins (vitamins A, D, E, and K) are stored in the body's fat.

  • Vitamin Function: Vitamins act as coenzymes or precursors to coenzymes.

Vitamin A

  • Function: Retinal is involved in visual processes as the pigment in rhodopsin and also works as a hormone.

  • Source: Retinoids (like retinol) are present in meat. B-carotene, a precursor to vitamin A, is found in fruits and vegetables (especially carrots).

  • Deficiencies: Can result in night blindness, visual impairment, and growth disorders.

Vitamin D (calciol, cholecalciferol)

  • Function: A precursor, calcitriol (1,25-dihydroxycholecalciferol), regulates calcium metabolism.

  • Source: Synthesized in the skin upon exposure to UV light. Also found in some foods.

  • Deficiencies: Results in rickets in children and osteomalacia in adults, impacting bone mineralization. Key role in balancing calcium levels.

Vitamin E (Tocopherol)

  • Function: Antioxidant, protecting unsaturated lipids in cell membranes from oxidative damage by reactive oxygen species (ROS).

  • Source: Found in plant-based foods.

Vitamin K

  • Function: Essential for the carboxylation of glutamate residues resulting in Ca2+ binding sites in several calcium-dependent proteins (essential for blood clotting). Vitamin K is produced by intestinal bacteria.
  • Source: Found in vegetables and made by bacteria in the gut

Reactive Oxygen Species (ROS)

  • Formation: ROS are generated during cellular processes.

  • Role: Both necessary and dangerous. Production is a part of normal cellular function, while excessive ROS is dangerous to the cell. Necessary for various functions but excessive ROS is harmful.

Visual Processes

  • Rhodopsin: A light-sensitive pigment in rod cells of the retina that undergoes a conformational change when exposed to light leading to a signal cascade where ultimately light is detected.
  • Photoreceptor Cells: Rods and cones, that transmit light info to the brain.
  • Signal Cascade: A series of biochemical events that transmit light signals from the photoreceptors to the brain.

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