Q: Which of the following best explains why the lagging strand is synthesized in Okazaki fragments during DNA replication?

DNA polymerase can only add nucleotides in the $$5' \to 3'$$ direction, so the lagging strand, which runs $$3' \to 5'$$, must be synthesized discontinuously as the replication fork opens.

Question 1

Which of the following best explains why humans can digest starch but not cellulose, even though both are polymers of glucose?

Accepted Answer

Starch contains $$\alpha-1$$,4 glycosidic linkages, which human enzymes can hydrolyze, while cellulose contains $$\beta-1$$,4 glycosidic linkages, which human enzymes cannot break.

Question 2

A chain of 10 glucose monomers is built by condensation (dehydration) reactions. How many water molecules are released during this process?

Accepted Answer

$$9$$ water molecules, because each glycosidic bond forms by removing one water molecule and there are $$n-1$$ bonds in a chain of $$n$$ monomers.

Question 3

Which of the following statements about lipids is TRUE?

Accepted Answer

Lipids are not considered true polymers because they are not made from repeating monomer units joined by the same type of covalent bond.

Question 4

Which of the following best describes the difference between saturated and unsaturated fatty acids?

Accepted Answer

Saturated fatty acids have no double bonds and are usually solid at room temperature, while unsaturated fatty acids have one or more double bonds, causing kinks that make them liquid at room temperature.

Question 5

During the Hershey and Chase experiment, why was radioactive phosphorus ($$^{32}P) $$used to label DNA and radioactive sulfur ($$^{35}S) $$used to label protein?

Accepted Answer

$$^{32}P $$labels DNA because DNA contains phosphorus but not sulfur, and $$^{35}S $$labels protein because proteins contain sulfur (in amino acids like cysteine and methionine) but not phosphorus.

Question 6

A double-stranded DNA sample contains $$26\%$$ adenine. According to Chargaff's rules, what percentage of guanine does it contain?

Accepted Answer

$$24\%$$ guanine, because $$26\%$$ adenine pairs with $$26\%$$ thymine, leaving $$48\%$$ for guanine and cytosine, so $$48\% \div 2 = 24\%.$$

Question 7

Which of the following best describes semiconservative replication of DNA?

Accepted Answer

Each new DNA molecule consists of one parental (old) strand and one newly synthesized strand.

Question 8

Why is DNA polymerase unable to start synthesis of a new DNA strand without a primer?

Accepted Answer

DNA polymerase can only add nucleotides to an existing 3' hydroxyl ($$3'$$-$$\mathrm{OH}) $$group; it cannot initiate synthesis de novo.

Question 9

Which of the following best explains why the lagging strand is synthesized in Okazaki fragments during DNA replication?

Accepted Answer

DNA polymerase can only add nucleotides in the $$5' 	o 3'$$ direction, so the lagging strand, which runs $$3' 	o 5'$$, must be synthesized discontinuously as the replication fork opens.

Question 10

Which of the following is a function of telomeres in eukaryotic chromosomes?

Accepted Answer

They protect the ends of chromosomes from degradation and prevent the loss of important genetic information during DNA replication.

Question 11

Which of the following best describes the central dogma of molecular biology?

Accepted Answer

Genetic information flows from DNA to RNA to protein.

Question 12

A DNA template strand reads $$3'	ext{-}TAC\ AAG\ CCG\ ATT	ext{-}5'. $$Using the codon key: $$\mathrm{AUG} = 	ext{Met (start)}$$, $$\mathrm{UUC} = 	ext{Phe}$$, $$\mathrm{GGC} = 	ext{Gly}$$, $$\mathrm{UAA} = 	ext{stop}$$, what is the amino acid sequence of the polypeptide produced?

Accepted Answer

Met - Phe - Gly

Question 13

Which of the following statements about the genetic code is TRUE?

Accepted Answer

It is redundant (more than one codon can specify the same amino acid), unambiguous (each codon specifies only one amino acid), and nearly universal (shared by almost all organisms).

Question 14

Which of the following best describes the role of the spliceosome in eukaryotic gene expression?

Accepted Answer

It removes introns from pre-mRNA and joins exons together to form mature mRNA.

Question 15

Which of the following is a correct match between a protein involved in DNA replication and its function?

Accepted Answer

Helicase: unwinds the DNA double helix at the replication fork.

Question 16

Which of the following best explains why eukaryotic chromosomes have multiple origins of replication?

Accepted Answer

Multiple origins allow the large amount of DNA in eukaryotic chromosomes to be replicated quickly and efficiently.

Question 17

Which of the following best describes the difference between euchromatin and heterochromatin?

Accepted Answer

Euchromatin is less condensed and more likely to be actively transcribed, while heterochromatin is highly condensed and generally transcriptionally inactive.

Question 18

Which of the following best describes the structure of a nucleotide?

Accepted Answer

A nucleotide consists of a phosphate group, a five-carbon sugar, and a nitrogenous base.

Question 19

Which of the following best explains why partially hydrogenated vegetable oils (trans fats) are considered a health concern?

Accepted Answer

Trans fats have trans double bonds, which make them more linear and solid at room temperature, and they have been linked to increased risk of heart disease.

Unit II Review: Structure and Function of Biological Molecules, Inheritance, and Gene Expression

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