The Genetic Code and DNA

What does DNA stand for?

Deoxyribonucleic acid.

What is the main function of DNA?

To store and transmit genetic information.

What does RNA stand for?

Ribonucleic acid.

What is the main function of RNA?

To participate in protein synthesis and gene regulation.

What is the secondary structure of DNA?

A double helix.

How are the two strands of DNA arranged?

Antiparallel.

What does antiparallel mean?

One strand runs 5′ to 3′ while the other runs 3′ to 5′.

What makes up the DNA backbone?

Alternating deoxyribose sugars and phosphate groups.

What sugar is present in DNA?

Deoxyribose.

What are the four nitrogenous bases in DNA?

Adenine, thymine, guanine, and cytosine.

Which DNA base pairs with adenine?

Thymine.

Which DNA base pairs with guanine?

Cytosine.

What type of bonds hold complementary DNA bases together?

Hydrogen bonds.

How many hydrogen bonds form between adenine and thymine?

Two.

How many hydrogen bonds form between guanine and cytosine?

Three.

Which base pair is stronger, A–T or G–C?

G–C because it has three hydrogen bonds.

What does Chargaff’s rule state?

In double-stranded DNA, the amount of adenine equals thymine and the amount of guanine equals cytosine.

If DNA contains 30% adenine, what percent is thymine?

30%.

If DNA contains 30% adenine, what percent is guanine?

20%.

If DNA contains 30% adenine, what percent is cytosine?

20%.

Is RNA usually single-stranded or double-stranded?

Single-stranded.

What makes up the RNA backbone?

Alternating ribose sugars and phosphate groups.

What sugar is present in RNA?

Ribose.

What are the four nitrogenous bases in RNA?

Adenine, uracil, guanine, and cytosine.

Which base is present in RNA instead of thymine?

Uracil.

Can RNA form secondary structures?

Yes, it can fold into structures such as hairpin loops.

What is a nucleotide made of?

A nitrogenous base, a pentose sugar, and one or more phosphate groups.

What are nucleotides the building blocks of?

Nucleic acids.

What type of bond links nucleotides together?

A phosphodiester bond.

Between which carbons does a phosphodiester bond form?

The 3′ carbon of one sugar and the 5′ carbon of the next sugar.

What are the purines?

Adenine and guanine.

How many rings do purines have?

Two rings.

What is the memory trick for purines?

Pure As Gold: adenine and guanine.

What are the pyrimidines?

Cytosine, thymine, and uracil.

How many rings do pyrimidines have?

One ring.

Which pyrimidine is found only in DNA?

Thymine.

Which pyrimidine is found only in RNA?

Uracil.

What is the memory trick for pyrimidines?

CUT the PY: cytosine, uracil, and thymine are pyrimidines.

How many hydrogen bonds form between A and T or A and U?

Two.

How many hydrogen bonds form between G and C?

Three.

What is DNA denaturation?

The separation of DNA strands by breaking hydrogen bonds.

What can cause DNA denaturation?

Heat, extreme pH, or certain chemicals.

Does DNA denaturation break phosphodiester bonds?

No, it breaks hydrogen bonds between bases.

What is melting temperature, or Tm?

The temperature at which 50% of DNA strands have separated.

How does a higher G–C content affect DNA melting temperature?

It increases the melting temperature.

Why does G–C-rich DNA have a higher melting temperature?

G–C pairs have three hydrogen bonds.

What is annealing?

The reassociation of complementary nucleic acid strands.

What is the reverse of DNA denaturation?

Annealing.

Why is DNA more stable than RNA?

DNA lacks a hydroxyl group at the 2′ carbon.

Why is RNA more reactive and less stable than DNA?

RNA has a hydroxyl group at the 2′ carbon.

Which nucleic acid is best suited for long-term genetic storage?

DNA.

Which nucleic acid is commonly involved in temporary and functional roles?

RNA.

How do structural differences between DNA and RNA affect their functions?

DNA is more stable for long-term storage, while RNA is more reactive and suited for protein synthesis and regulation.

Why is complementary base pairing important?

It allows accurate replication, transcription, and stable nucleic acid structure.

Why is the antiparallel nature of DNA important?

Polymerases read and synthesize nucleic acids in specific directions.

What is the central dogma of molecular biology?

DNA → RNA → protein.

What process converts DNA into RNA?

Transcription.

What process converts RNA into protein?

Translation.

In what direction does genetic information usually flow?

From DNA to RNA to protein.

What is a major exception to the central dogma?

Reverse transcription from RNA to DNA.

What enzyme carries out reverse transcription?

Reverse transcriptase.

What types of organisms or viruses commonly use reverse transcriptase?

Retroviruses and some RNA viruses.

What did the Hershey–Chase experiment establish?

DNA is the heritable genetic material.

What organisms were used in the Hershey–Chase experiment?

Bacteriophages and bacteria.

What radioactive isotope was used to label DNA in the Hershey–Chase experiment?

Radioactive phosphorus.

Why was radioactive phosphorus used to label DNA?

DNA contains phosphorus in its phosphate backbone.

What radioactive isotope was used to label protein in the Hershey–Chase experiment?

Radioactive sulfur.

Why was radioactive sulfur used to label protein?

Some amino acids contain sulfur, while DNA does not.

What entered the bacterial cells in the Hershey–Chase experiment?

Phage DNA.

What remained outside the bacterial cells in the Hershey–Chase experiment?

Most of the phage protein coats.

What conclusion came from the Hershey–Chase experiment?

DNA, not protein, carries genetic information.

What does DNA store and transmit?

Genetic information.

From what molecule is RNA transcribed?

DNA.

What is mRNA?

Messenger RNA that carries genetic information from DNA to ribosomes.

What is the main function of mRNA?

To carry the code for protein synthesis.

Where does mRNA deliver genetic information?

To ribosomes.

What is hnRNA?

Heterogeneous nuclear RNA, the precursor to mature mRNA.

What happens to hnRNA?

It is processed into mature mRNA.

What is tRNA?

Transfer RNA that carries amino acids to the ribosome.

What is the shape of tRNA?

A cloverleaf structure.

What is the main function of tRNA?

To bring specific amino acids to the ribosome during translation.

What part of tRNA pairs with an mRNA codon?

The anticodon.

What is rRNA?

Ribosomal RNA.

What is the function of rRNA?

It forms part of the ribosome and helps catalyze peptide bond formation.

What is a ribozyme?

An RNA molecule with catalytic activity.

What is an example of a ribozyme?

rRNA.

What are siRNA and miRNA?

Small RNA molecules that regulate gene expression.

What do siRNA and miRNA usually do?

Downregulate gene expression.

How can siRNA or miRNA reduce gene expression?

By promoting mRNA degradation or blocking translation.

Does all RNA become translated into protein?

No.

What is noncoding RNA?

RNA that is not translated into protein.

What are examples of noncoding RNA?

tRNA, rRNA, miRNA, and siRNA.

What does reverse transcriptase produce from an RNA template?

DNA.

How are ribosomes involved in translation?

They read mRNA codons and assemble amino acids into a protein.

What is a codon?

A three-nucleotide sequence in mRNA.

How many possible codons are there?

64.

Why are there 64 codons?

Four bases can be arranged in groups of three, giving 4³ = 64 combinations.

What does it mean that the genetic code is degenerate?

Multiple codons can code for the same amino acid.

Does degeneracy mean one codon codes for several amino acids?

No, each codon specifies only one amino acid or stop signal.

What is the start codon?

AUG.