Electrical excitation for heart contraction originates in the ________ .

a. atrioventricular (AV) node
b. Purkinje fibers
c. intercalated disc
d. sinoatrial (SA) node
e. cardiac muscle cells


d. sinoatrial (SA) node

Biology & Microbiology

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The most common DNA-binding motif is the  

A.  non-helical zipper. B.  leucine zipper. C.  zinc finger. D.  homeodomain. E.  helix-turn-helix.

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Crossing over is partially responsible for our genetic diversity

a. True b. False Indicate whether the statement is true or false

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Gram-negative bacteria are less susceptible to complement lysis than Gram-positive bacteria

Indicate whether this statement is true or false.

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What is one cause for the 21,000 protein encoding sequences in the human genome producing between 200,000 and 1 million different proteins?

A) SNPs B) CRISPR-Cas systems C) alternative splicing D) CNVs E) restriction enzymes

Biology & Microbiology