Answer:
peptide antigens by MHC class II molecules
Explanation:
Helper T cells are activated by peptide antigens by MHC class II molecules. These antigens express on the surface of antigen-presenting cells (APCs). After activation, the T helper cells divide and secrete cytokines to assist the immune response.
Cytokinesis occurs after mitosis is complete. It is when two daughter cells are formed, each with their own nuclei, after a single cell has <em>completely </em>divided.
<span>The propositions are:
a. forms glucose from </span><span>noncarbohydrates
b. does all of these
c. destroys damaged red blood cells
d. stores vitamin D
e. forms urea
The right answer is: B. </span>does all of these
*The liver plays a role in the metabolism of carbohydrates:- gluconeogenesis (manufacture of a new glucose molecule from a non-carbohydrate molecule);- glycogenolysis (release of glucose from glycogen) under the effect of glucagon;- gluconeogenesis (storage of glucose in the form of glycogen) under the effect of insulin
*It stores fat-soluble vitamins (A, D, K and E) and glycogen.*It converts ammonia to urea (detoxification)<span>*It recycles substances from the senescent red blood cells.</span>
Answer:
<u>3) Uncontrolled cell division occurred as a result of gene mutations</u>
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Explanation:
Spontaneous modifications within the genome may occur during the process of cell division. When copies of the DNA inside the cell are made, these mutations cause errors; and can include small single nucleotide polymorphisms, and large scale additions or deletions across multiple genes.
Some, like somatic mutations, exist only inside vegetative (body) cells, that cannot be passed onto offspring. This is caused by several factors like
- UV radiation,
- chemical mutagens,
- infective agents
UV radiation damages strands of DNA, by causing dimers to form; here, consecutive nucleotide bases covalently bond instead of those on the complementary strand. This conformational change causes errors in DNA proofreading and repair mechanisms where bases are not well-incorporated into the strand- tumors (clumps of uncontrolled cell growth) may form, resulting in melanoma, a type of skin cancer.