Ch 9

What holds one DNA strand against the other in the double helix?

Hydrogen bonds hold the two strands of DNA together in the double helix.

What is a codon?

A codon is a three-nucleotide sequence on mRNA that codes for a specific amino acid.

Why doesn't an A or T form two hydrogen bonds with G or C in a DNA double helix?

Adenine (A) pairs with Thymine (T) via two hydrogen bonds, while Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.

Is the complementary strand for 'AAAGGG' TTTAAA correct?

Yes, because A pairs with T and G pairs with C following complementary base-pairing rules.

What would the complementary messenger RNA code be for the DNA sequence (TAGGCAT)?

The complementary mRNA sequence would be AUCCGUA.

If an mRNA is missing an 'AUG' codon, will it be translated? Why?

No, because AUG is the start codon that signals the beginning of translation.

True or False: The anticodon is found on a complementary DNA strand.

False. The anticodon is found on tRNA, not DNA.

What directs the formation of a polypeptide (protein)?

A gene.

What are non-coding portions of the DNA molecule called?

Introns.

What is the code for phenylalanine in Escherichia coli if it is UUU in humans?

UUU. The genetic code is universal across organisms.

What enzyme causes DNA molecules to split apart during replication?

Helicase.

What are the three types of RNA?

Messenger RNA (mRNA), Ribosomal RNA (rRNA), and Transfer RNA (tRNA).

Describe mRNA.

mRNA carries genetic information from DNA to the ribosome for protein synthesis.

Why is DNA replication described as a semiconservative process?

Each new DNA molecule consists of one original strand and one newly synthesized strand.

What would happen if helicases were missing during replication?

The DNA strands would not separate, preventing replication from occurring.

If thymine makes up 15 percent of the bases in a specific DNA molecule, what percentage of the bases is cytosine?

35%.

During DNA replication, what strand is replicated in a discontinuous fashion?

The lagging strand.

What synthesizes new DNA strands?

DNA polymerase.

How are replication and transcription similar?

Both involve the synthesis of a new nucleic acid strand using a DNA template.

How are replication and transcription different?

Replication produces an identical DNA copy, while transcription produces RNA.

What is the function of the ribosome during translation?

The ribosome reads mRNA and assembles amino acids into a protein.

What is the function of tRNA during translation?

tRNA carries amino acids to the ribosome and matches them with the correct codons.

What is the anticodon for the tRNA that carries methionine to the ribosome?

UAC.

True or False: The first amino acid is always methionine.

True.

What are the letters in DNA replication and transcription/translation?

A, T, C, G (DNA); A, U, C, G (RNA).

What are the instructions in DNA replication and transcription/translation?

Genes provide the instructions to assemble proteins.

Will a protein still function if a nucleotide is changed? Why or why not?

It depends. Some mutations are silent, while others change amino acids and alter function.

What is the role of cAMP in the positive inducible lactose operon?

cAMP binds to the CAP protein to activate the lac operon, allowing transcription of lactose-digesting enzymes.

What is an intron?

An intron is a non-coding sequence of DNA that is removed from pre-mRNA during RNA processing.

What is an exon?

A coding sequence of DNA that remains in mature mRNA and is translated into protein.

What role does cAMP play in the positive inducible lactose operon?

It binds to the CAP protein to form a complex that activates the lac operon.

What describes horizontal gene transfer?

Transfer of genetic material between organisms without sexual reproduction.

What describes vertical gene transfer?

Genetic transfer from parent to offspring.

What is transduction?

Virus transfers DNA between bacteria.

What is conjugation?

DNA transfer between bacteria through a pilus.

What does the term 'degenerate' refer to in genetics?

Multiple codons can code for the same amino acid.

What is a mutation?

A change in DNA sequence.

What is the difference between point mutations and frameshift mutations?

Point mutations involve a change in one base, while frameshift mutations involve the insertion or deletion of bases causing a shift in the reading frame.

What is the significance of the AUG start codon?

It signals the beginning of translation.

What is the function of the ribosomal large subunit?

It forms peptide bonds between amino acids during translation.

What do aminoacyl-tRNA synthetase enzymes do?

They attach the correct amino acid to its corresponding tRNA.