b. Nerves C. Skin d. Lung epithelium e. Heart During fertilization in invertebra

Question

b. Nerves C. Skin d. Lung epithelium e. Heart During fertilization in invertebrates, what is the earliest event to occur in the process? a. Sperm contacts the cortical granules around the egg b. Sperm nucleic acid enters the egg's cytoplasm to form a pronucleus c. Acrosome releases hydrolytic enzymes d. Sperm contacts the vitelline membrane around the egg e. Hyaluronic acid forms a barrier to prevent polyspermy Regions of chromosomes that are not transcriptionally active are referred to as: a. Heterochromatin b. Euchromatin c. Repetitive DNA d. Satellite DNA The 5' end of a polynucleotide chain contains the chemical group a. Amino group b. Carboxyl group c. Hydroxyl group d. Carbonyl group e. Phosphate group DNA polymerases do not initiate DNA synthesis de novo, without a priming end. Priming in vivo is achieved by synthesis of a short fragment of which is later removed by the activity of DNA polymerase I in eukaryotes a. b. c. d. RNA, 5 to 3 exonuclease DNA, 3 to5, exonuclease Protein, 5 to 3, endonuclease RNA, 3 to 5, endonuclease In the genetic code, triplets of nucleotides(codons) specify the amino acids to be added during protein synthesis. What is the total number of codons in nature? b. 4 c. 16 d. 32 e. 64 Proteins that are destined to be secreted from eukaryotic cells are synthesized on a. The outer mitochondrial membrane

Explanation / Answer

(d) In invertebrates, the plasma membrane of the tip of spermatozoa binds to the vitelline coat surrounding the outer surface of the plasma membrane of the ovum.

(a) Heterochromatin is tightly packed DNA which makes it unacessible to polymerase and hence is not transcribed actively.

(e) The 5` end of a polynucleotide chain has a terminal phosphate group whereas 3` end has a terminal hydroxyl group.

(a)  Primase synthesizes short RNA primers with a free 3`OH group that is elongated by DNA polymerase by addition of dNTPs complementary to the template strand. The RNA primers are then removed by 5`-3` exonuclease activity of DNA polymerase and replaced it with DNA strand.

(e) The 20 amino acids are encoded by the four nucleotides, each amino acid being encoded by a triplet of nucleotides.

Hence, total number of nucleotides= 43= 64 codons.

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