BIO101 Exam 4 Review

Hershey and Chase's experiment helped establish DNA as the genetic material by studying:

•  Mice and bacterial strains

• Viruses and bacteria

• Ribosomes and proteins

• Enzymes and RNA

The structure of DNA is known as:

• single helix

• alpha helix

• beta helix

• double helix

Chargaff’s rules state that:

• A pairs with G and T pairs with C

• A pairs with T and G pairs with C

• A pairs with C and T pairs with G

• A pairs with C and T pairs with G

Rosalind Franklin’s x-ray crystallography was critical because it revealed:

• DNA’s double-helix structure

• Base pairing rules

• DNA’s sugar-phosphate backbone

• The sequence of nucleotides

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Transfer RNA (tRNA) carries genetic instructions from DNA to ribosomes.

• True

• False

• Only in eukaryotes

• Only under specific conditions

Answer explanation

tRNA doesn’t carry genetic instructions. It brings amino acids to the ribosome. mRNA carries the instructions from DNA to the ribosome.

Which statement about DNA replication is NOT correct?

• DNA polymerase catalyzes replication

• Replication uses one old strand as a template

• DNA replication forms identical molecules

• Bases pair with others exactly like themselves

Answer explanation

DNA replication involves complementary base pairing (A pairs with T, and G pairs with C), not bases pairing with identical ones.

This ensures accurate replication of the DNA sequence.

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The enzyme that unzips DNA during replication is:

• DNA polymerase

• Helicase

• Primase

• Ligase

Answer explanation

Helicase unwinds and separates the two strands of the DNA helix, allowing replication to occur.

It breaks the hydrogen bonds between complementary bases.

The synthesis of new DNA strands is carried out by:

• DNA polymerase III

• DNA polymerase I

• Helicase

• Ligase

Answer explanation

DNA polymerase III is the main enzyme that adds nucleotides to the growing DNA strand during replication.

It works in the 5’ to 3’ direction.

DNA polymerase adds nucleotides in which direction?

• 3' to 5' only

• 5' to 3' only

• Both directions simultaneously

• Depends on the strand

Answer explanation

DNA polymerase can only add nucleotides to the 3’ end of a growing strand, so replication always proceeds in the 5’ to 3’ direction.

Which of the following is NOT true about the genetic code?

• Each codon consists of three bases

• Many amino acids have multiple codons

• Each base codes for three amino acids

• It includes start and stop codons

Answer explanation

Each codon (a set of three bases) codes for one amino acid, not three.

The genetic code is universal and redundant, allowing multiple codons for some amino acids.

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