Biology

Molecular Biology and Genetics

717 Questions

Molecular biology and genetics explore the structure and function of DNA, RNA, genetic mutations, and heredity. Understanding these building blocks of life is essential for most biology examinations. Review these practice questions to test your molecular genetics knowledge.

DNA structure and basesGenetic mutationsNucleic acids compositionDNA sequencing and replication

Molecular Biology and Genetics Questions

Multiple choice

Which of the following is an example of the degeneracy of the genetic code?

  1. A given amino acid has more than one codon

  2. Each codon specifies more than one amino acid

  3. The first two bases specify the amino acid

  4. The genetic code is not degenerated

  5. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The degeneracy of the genetic code means that most amino acids are specified by more than one codon. For example, leucine has six different codons. This redundancy buffers against mutations.

Multiple choice

The feature that best refers to the melting temperature of DNA is

  1. the temperature at which the entire DNA is denatured

  2. the length of DNA

  3. the proportion of G-C content of DNA

  4. the proportion of the purine content of DNA

  5. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

DNA melting temperature (Tm) is primarily determined by GC content because G-C pairs form three hydrogen bonds versus two for A-T pairs. Higher GC content means higher Tm due to stronger bonding.

Multiple choice

How many codons make the genetic code?

  1. 4

  2. 16

  3. 64

  4. 46

  5. 20
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

If nucleotides are arranged in units of three, the possible nucleotide combination will be 4 x 4 x 4 = 64 codons, which are more than sufficient for 20 amino acids.

Multiple choice

'A genetic code is degenerate.' What is meant by this statement?

  1. A genetic code is a triplet like UUU.

  2. There are no commas in the genetic code.

  3. Three codons are for amino acid serine.

  4. There are both initiation and termination codons.

  5. The codes are non-overlapping.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Presence of more then one codon for an amino acid is called degeneracy.

Multiple choice

Which of the following is a set of primary nucleic acid sequence databases?

  1. PIR, MIPS, SWISS-PROT

  2. TrEMBL, NRL-3D, EMBL

  3. EMBL, TrEMBL, GenBank

  4. EMBL, GenBank, DDBJ

  5. SWISS-PROT, EMBL, TrEMBL
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Correct answer. EMBL, GenBank and DDBJ are primary nucleic acid sequence databases. Primary database is a database that stores biomolecular sequences of proteins, nucleic acids, etc. and associated annotation information of organism, species, function, etc.

Multiple choice

Identify the incorrect option for prokaryotic cell.

  1. Size is 1 to 10 μm.

  2. Double stranded DNA is present.

  3. DNA is not associated with histone sugar.

  4. Nucleolus is 0.01 to 0.5 μm in size.

  5. Membrane bound cell organelles are absent.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Nucleolus is absent in prokaryotic cell.

Multiple choice

In a solution of nucleotides, made from a ground-up segment of DNA, adenine makes up 33% of the solution. What percentage of the solution would be guanine?

  1. 17%

  2. 27%

  3. 24%

  4. 33%
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to Chargaff's rules, in double-stranded DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). If adenine is 33%, then thymine is also 33%. This accounts for 66% of the nucleotides. The remaining 34% must be guanine + cytosine in equal proportions, so guanine is 17% and cytosine is 17%.

Multiple choice

Which of the following is a valid contrast between RNA and DNA?

  1. RNA - found only in the nucleus DNA - found in the nucleus and the cytoplasm

  2. RNA - thymine is one of its bases DNA - uracil is one of its bases

  3. RNA - helical DNA - not helical

  4. RNA - sugar is ribose DNA - sugar is deoxyribose
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

RNA contains the sugar ribose, while DNA contains deoxyribose. This is a fundamental biochemical difference - the 'deoxy' in DNA means it lacks one oxygen atom that ribose has. RNA is found in both nucleus and cytoplasm, not only nucleus. DNA uses thymine and RNA uses uracil, not the reverse. Both RNA and DNA can form helical structures (RNA can be single-stranded but also forms helices like in tRNA).