Coombs’ reagent is an antiserum with antibodies that bind to human

Coombs reagent is an antiserum with antibodies that bind to the human antibodies attached on the surface of the erythrocytes.

Explanation:

Coombs test is a blood test used in immunology and immunohematology. It is of two types: direct and indirect.

The Coombs reagent is an antiserum, containing antibodies.

The direct Coombs test detects the antibodies present on the surface of the erythrocytes.

In this test, when the Coombs reagent is reacted with the blood to be tested, the antibodies in the Coombs reagent binds to the antibodies attached on the surface of the erythrocytes in the test blood and cause agglutination.

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step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.