Chapter 4 Nucleic Acids

Question 1

What are the components of a nucleotide?

Answer 1

Phosphate, Pentose sugar, Nitrogen-containing bases

DNA contains deoxyribose; RNA contains ribose.

Question 2

Which bases are classified as purines?

Answer 2

Adenine, Guanine

Purines have 2 nitrogen-containing rings.

Question 3

Which bases are classified as pyrimidines?

Answer 3

Thymine, Cytosine, Uracil

Pyrimidines have 1 nitrogen-containing ring.

Question 4

What is the function of adenosine triphosphate (ATP)?

Answer 4

Universal energy carrier, releases energy for metabolic activities

ATP can be hydrolyzed to ADP and AMP.

Question 5

What is the structure of DNA?

Answer 5

Macromolecule, polymer of nucleotides, double stranded, helix

Synthesized during interphase, located in the nucleus in chromosomes.

Question 6

What is a gene?

Answer 6

Length of DNA that codes for one or more polypeptide chains

Genes occupy a specific location on a chromosome called a locus.

Question 7

What is the human genome composed of?

Answer 7

Approximately 25,000 genes

Some genes are also located in the mitochondria.

Question 8

What stabilizes the DNA molecule?

Answer 8

Covalent bonds (phosphodiester bonds), histone coat

These provide strength and stability to the sugar-phosphate backbone.

Question 9

Define complementary base pairing.

Answer 9

Specific pairing of nitrogenous bases ensuring identical sequences after replication

Errors are corrected by DNA polymerase.

Question 10

What happens if one strand of DNA is damaged?

Answer 10

Information is not lost; the complementary strand can be used to rebuild it

This feature contributes to DNA’s stability.

Question 11

What are Chargaff’s rules?

Answer 11

1) Number of one purine equals number of one pyrimidine; 2) Composition varies between species

A=T and C=G pairing ensures DNA is a constant width.

Question 12

What is semi-conservative replication?

Answer 12

Each new DNA molecule retains one original polynucleotide strand

It produces identical sister chromatids prior to mitosis.

Question 13

What did Meselson and Stahl’s experiment demonstrate?

Answer 13

DNA replication is semi-conservative

They used isotopes of nitrogen to distinguish between DNA densities.

Question 14

What safety precautions should be taken when using ethanol for DNA purification?

Answer 14

Use ice-cold ethanol, avoid spark-prone environments

Ethanol vapors can be flammable and lead to explosions.

Question 15

What is a mutation?

Answer 15

Spontaneous change in the quantity or arrangement of DNA

This includes changes in the nucleotide sequence of the genome.

Question 16

What are mutagens?

Answer 16

Substances that cause mutations, e.g., tar, mustard gas, radiation

They can induce changes during DNA replication.

Question 17

What is the definition of mutations?

Answer 17

Spontaneous or random change in the quantity or arrangement of DNA, i.e., change in the nucleotide sequence of the genome.

Question 18

What can cause mutations?

Answer 18

Mutagens such as tar, mustard gas, benzene, or radiation: UV light, X-rays, gamma rays.

Question 19

When do mutations occur?

Answer 19

They occur randomly during DNA replication in interphase.

Question 20

What are somatic mutations?

Answer 20

Mutations that occur during mitosis, leading to aging and cancer.

Question 21

How do mutations in gametes differ from somatic mutations?

Answer 21

Gamete mutations can be inherited and occur during meiosis, affecting future generations.

Question 22

What are chromosome mutations?

Answer 22

Changes to the structure (whole or part) of a chromosome, including deletion(s), insertion(s), or translocation(s).

Question 23

Define DNA point mutations.

Answer 23

Changes to the structure of a gene due to a change in the nucleotide base sequence.

Question 24

What is a substitution mutation?

Answer 24

Occurs when one base is substituted for another, potentially affecting only 1 triplet.

Question 25

What is a deletion mutation?

Answer 25

Removal of one or more bases, causing a frameshift and affecting many triplets.

Question 26

What is an insertion mutation?

Answer 26

Addition of one or more bases, causing a frameshift and affecting many triplets.

Question 27

What happens to codons after an insertion or deletion of a base?

Answer 27

Codons after the insertion/deletion will all be altered, potentially leading to a truncated polypeptide or a new sequence of amino acids.

Question 28

Do point mutations always affect protein function?

Answer 28

No, because each amino acid is coded for by more than one codon and the code is degenerate.

Question 29

What is the biological importance of mutations?

Answer 29

Mutations contribute to evolution, cancer, and immune system development.

Question 30

Give an example of a beneficial mutation.

Answer 30

Production of melanin in early humans in Africa for UV protection and vitamin D synthesis.

Question 31

What is the triplet code in the genetic code?

Answer 31

A sequence of 3 nucleotide bases called a codon, where each codon codes for one specific amino acid.

Question 32

What is meant by a degenerate code?

Answer 32

All amino acids (except methionine) have more than one codon.

Question 33

What does it mean that the genetic code is non-overlapping?

Answer 33

Each base is only part of one codon, with each triplet read separately.

Question 34

What are the two main types of nucleic acids?

Answer 34

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

Question 35

What are the functions of DNA?

Answer 35

Carries genetic information, consists of introns and exons, codes for specific polypeptides.

Question 36

What is the structure of mRNA?

Answer 36

Carries the same sequence of nucleotide bases as the coding strand of DNA, but with uracil instead of thymine.

Question 37

What is the role of tRNA?

Answer 37

Carries specific amino acids to ribosomes according to its anticodon.

Question 38

What is the function of ribosomal RNA (rRNA)?

Answer 38

Forms the ribosome's subunits and acts as an enzyme to join amino acids during translation.

Question 39

What are the key differences between DNA and RNA?

Answer 39

DNA is double-stranded, contains deoxyribose and thymine; RNA is single-stranded, contains ribose and uracil.

Question 40

What is transcription?

Answer 40

The synthesis of a mRNA molecule with a complementary sequence to a section of DNA.

Question 41

What occurs during transcription?

Answer 41

RNA polymerase synthesizes mRNA in the nucleoplasm, unwinding DNA and adding RNA nucleotides.

Question 42

What is alternative splicing?

Answer 42

The process of joining exons together in different combinations to form mature mRNA.

Question 43

What is the purpose of translation?

Answer 43

Production of a specific polypeptide chain from the code sequence of mRNA at ribosomes.

Question 44

What is the first codon in mRNA during translation?

Answer 44

AUG, which codes for the amino acid methionine.

Question 45

What is the role of ribosomes in translation?

Answer 45

Site where mRNA is read and polypeptide chains are synthesized.

Question 46

What is the function of peptidyl transferase?

Answer 46

Catalyzes the formation of peptide bonds between adjacent amino acids during translation.

Question 47

What are anticodons?

Answer 47

Sequences of 3 exposed RNA-nucleotides on tRNA specific for one amino acid.

Question 48

What are codons?

Answer 48

Sequences of 3 nucleotide bases found on mRNA and DNA.