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 zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

In DNA, adenine pairs with

  1. Guanine

  2. Thymine

  3. Cytosine

  4. Uracil
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The nitrogenous bases present in the DNA are purines and pyrimidines. The purines are adenine and guanine. The pyrimidines are thymine and cytosine. The purines are double ring structure while the pyrimidines are the single ring made up of carbon and nitrogen. Purines pair with the pyrimidines by hydrogen bonds. Adenine pairs with thymine by two hydrogen bond while the cytosine pairs with the guanosine by three hydrogen bonds.

So, the correct answer is option B.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

DNA is composed of repeating units of

  1. Ribonucleosides

  2. Deoxyribonucleosides

  3. Ribonucleotides

  4. Deoxyribonucleotides
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
DNA is a chain of polynucleotide which are joined by the phosphodiester bonds. The nucleotide consists of a deoxyribose sugar, nitrogenous bases, and phosphate.The two nucleotide is linked by the phosphodiester bond. It is formed by the linkage between the 3' carbon atom of one sugar molecule and the 5' carbon atom of another. Two hydroxyls (OH) groups on the phosphate molecule bind to the 3’ and 5’ carbons on two independent pentose sugars to form a bond.
So, the correct answer is option D.
Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

Base pairs present in one turn of DNA are

  1. $12$
  2. $11$
  3. $10$
  4. $9$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
DNA has the double helical structure where the two strands are tightly coiled over each other. B- DNA has right-handed helix with the major and minor groove. The diameter of the DNA is 20 A$^o$. The distance between base pairs is 3.4 A$^o$. The total length of one turn of DNA is 34 A$^o$. The total number of the base pair in each turn is 34/3.4 = 10.
So, the correct answer is option C.
Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

The similarity between bacterial and eukaryotic DNA is that both are

  1. Circular

  2. Single stranded

  3. Double stranded

  4. All the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Nucleic acids are DNA and RNA. DNA is a genetic material which is mainly present in the nucleus of the cell in eukaryotes like mammals. The genetic material is covered by a nuclear membrane. In prokaryotes like bacteria the genetic material lie freely in the cytoplasm. The region where the nucleic acid are present is known as nucleoid. The similarity between bacterial and eukaryotic DNA is that both are double stranded DNA.
So, the correct answer is option C.
Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

Length of one turn of DNA is

  1. $34 \mathring{A}$
  2. $3.4 \mathring{A}$
  3. $0.34 \mathring{A}$
  4. $20 \mathring{A}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
DNA has the double helical structure where the two strands are tightly coiled over each other. B- DNA has right-handed helix with the major and minor groove. The diameter of the DNA is 20 A$^o$. The number of base pairs in one turn is 10 and the distance between base pairs is 3.4 A$^o$. So the total length of one turn of DNA is 10 x 3.4 =  34 A$^o$.
So, the correct answer is option A.
Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

The two strands of DNA are held together by bonds of

  1. Nitrogen

  2. Oxygen

  3. Hydrogen

  4. Carbon
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
The nitrogenous bases present in the DNA are purines and pyrimidines. Purines are double ring while pyrimidines are single ring structure. Adenine and guanine are purines while thymine, uracil, and cytosine are pyrimidines. A purine is attached to pyrimidine by hydrogen bond. Adenine is attached to thymine by two hydrogen bonds while three hydrogen bond is present between guanine and cytosine.
So, the correct answer is option C.
Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

DNA is very long. It is accommodated in small sized nucleus by

  1. DNA-ase digestion

  2. Super coiling

  3. Elimination of repetitive DNA

  4. Deletion of non-essential genes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

DNA is very long. It is accommodated in the small-sized nucleus by super coiling. The enzyme topoisomerase helps in the supercoiling of the DNA which helps in packaging and some biological process. The super coiled DNA is uncoiled during the process of transcription and translation. During transcription the enzyme helicase cuts the phosphate backbone and separates the two super coiled DNA strands while the topoisomerase balances the strain and prevents the recoiling of the DNA.

So, the correct answer is option B.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

A $68nm$ length double stranded DNA has 24 adenine nucleotices. What must be the number of guanine nucleotides?

  1. $48$
  2. $72$
  3. $76$
  4. $176$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Length of $3.4 nm $ includes $10$ base pairs.So, $68 nm $ will include $200$ base pairs that is $400$ bases.

A=T AND G=C,
A+T+G+C=$400$,
$24$+$24$+$2G$=$400$.,
$2G$ = $352$.
So, Guanine nucleotides would be $176$.
Hence, the correct answer is option D.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

The genetic information in the body is encoded in the

  1. Structural proteins

  2. Enzymes

  3. DNA

  4. DNA and enzymes
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Deoxyribose Nucleic Acid or DNA carries the genetic information in the form of small segments known as genes and is also the genetic material in various organisms including humans.

Structural proteins and enzymes are the gene products that are synthesised from DNA through the process of translation.
Hence, the correct answer is 'DNA'.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

Which of the following general statement about the structure of DNA is true?

  1. The hydrogen bonds connecting base pairs exist in a polar environment.

  2. Both major and minor grooves are formed between the phosphate-sugar backbone.

  3. The same C and N atoms are present in each groove.

  4. The amount of energy required to break down the AT and GC pairs is the same.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The DNA double helical structure has two different environments. The nitrogenous bases have an aromatic ring structure and are hydrophobic and interact with each other through base pair stacking interactions. At the same time, the back bone of DNA formed by phosphodiester bonds is hydrophilic and interacts with water. The nitrogenous bases of one nucleotide chain form hydrogen bonds with the nitrogenous bases present directly opposite them on the other chain. The hydrogen bonds are formed in polar aqueous environment. The adenine base pairs with thymine with two hydrogen bonds and guanine base pairs with cytosine with three hydrogen bonds.
So, the correct answer is option A.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

If there are 10,000 base pairs in DNA, then its length

  1. 340 nm

  2. 3400 nm

  3. 34000 nm

  4. 340000 nm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to the most widely accepted model of DNA structure, the distance between any two base pairs in DNA is approximately 3.4 angstroms. Thus for a DNA molecule having 10,000 base pairs; the length will be 10,000 x 3.4 or 34000 angstroms or 3400 nanometers.
So, the correct answer is option B.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

In a DNA sample the proportion of A is 17%, the amount of G + T and C will be respectively.

  1. 50% and 33%

  2. 66% and 17%

  3. 66% and 33%

  4. 33% and 50%
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In any double stranded DNA, adenine (A) pairs with a thymine (T) and Guanine (G) pairs with a cytosine (C).
Now, since each A always pairs with a T, the percentage of A and T will always be the same. Therefore, percentage of T will also be 17%.
So we can conclude that A+T=17+17=34%
The rest would account for G+C which would be 100-34=66%, thus G+C=66%.

Now, since each G always pairs with a C, thus the individual proportions of G and C will be 33%. 
So we get the base composition of DNA as A=T=17% and G=C=33%
Therefore, G+T=33+17=50% and C=33%.
Hence the correct answer is '50% and 33%'.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

How many amino acids will be coded by the given sequence of ribonucleotides, if the 15$^{th}$ base is substituted by G?
'5AUGGUGUAGAGGUACCAU3'

  1. Four

  2. Five

  3. Six

  4. Two
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Amino acid synthesis stops when any STOP codon is encountered by ribosome. There are total 3 stop codons, UAG, UGA, UAA. Codons are always read in triplets. So the given ribonucleotide sequence will be read as: AUG,GUG, UAG, and so on. Notice that the third codon (UAG) is a stop codon, so the protein synthesis will stop at the third codon itself. It doesn't matter if the 15th base is substituted by G or not, the given sequence will code for only two amino acids, AUG (methionine) and GUG (Methionine)

So, the correct answer is 'Two'.

Multiple choice zoology structure of chromosome, cell cycle and cell division structure of dna nucleic acid heredity and inheritance

DNA cannot pass through a cell membrane as

  1. It is too big to cross the membrane

  2. It is a hydrophilic molecule

  3. Membrane does not have specific proteins to facilitate the transport

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

DNA cannot pass through a cell membrane as it is hydrophilic in nature whereas cell membrane is made up of lipid bilayer. 

So, the correct option is 'Option B' .