DNA Replication and the genetic code

Question 1

Why do cells divide, and how does DNA replication ensure genetic continuity?

Answer 1

Cells divide for growth and tissue repair. DNA replication ensures that daughter cells are genetically identical by creating new DNA strands with base sequences identical to the parent cell’s DNA.

Question 2

How does complementary base pairing contribute to DNA replication?

Answer 2

Complementary base pairing ensures that adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G), preserving the exact base sequence during replication.

Question 3

What is semi-conservative replication, and why is it important?

Answer 3

Semi-conservative replication produces two DNA molecules, each consisting of one original strand and one newly synthesized strand. This method ensures genetic consistency across generations of cells.

Question 4

What are the key steps in semi-conservative replication?

Answer 4

Unwinding
Base pairing
Bond Formation

Question 5

What happens during the unwinding phase in semi-conservative replication?

Answer 5

DNA helicase unwinds the double helix and separates strands by breaking hydrogen bonds.

Question 6

What happens during the Base Pairing phase in semi-conservative replication?

Answer 6

Free nucleotides pair with exposed bases using the complementary base pairing rule.

Question 7

What happens during the Bond Formation phase in semi-conservative replication?

Answer 7

DNA polymerase forms phosphodiester bonds between adjacent nucleotides, creating the sugar-phosphate backbone.

Question 8

What is the role of DNA helicase in replication?

Answer 8

DNA helicase unwinds the double helix and separates the two DNA strands by breaking hydrogen bonds between complementary bases.

Question 9

What does DNA helicase specifically do as it moves along the DNA strand?

Answer 9

It catalyzes reactions to break hydrogen bonds, exposing the template strands for replication.

Question 10

What is the role of DNA polymerase in replication?

Answer 10

DNA polymerase catalyzes the formation of phosphodiester bonds, linking nucleotides to form the sugar-phosphate backbone of the new strand.

Question 11

How does DNA polymerase ensure accuracy during replication?

Answer 11

It aligns nucleotides using complementary base pairing rules and has a proofreading function to correct errors.

Question 12

Why are enzymes specific in their roles during replication?

Answer 12

Enzymes have specific shapes that allow them to bind to certain molecules or regions of DNA, ensuring precise biochemical reactions like unzipping or bond formation.

Question 13

What happens during the unwinding of DNA?

Answer 13

The DNA double helix unwinds, and hydrogen bonds between base pairs are broken, exposing the bases for complementary pairing.

Question 14

What enables the unwinding of DNA?

Answer 14

The enzyme DNA helicase moves along the DNA molecule, breaking hydrogen bonds between complementary bases (A-T, C-G).

Question 15

How are free nucleotides incorporated into new DNA strands?

Answer 15

Free DNA nucleotides pair with exposed bases on the template strand using complementary base pairing (A-T, C-G). Hydrogen bonds form between these bases.

Question 16

How are adjacent nucleotides joined together?

Answer 16

DNA polymerase forms phosphodiester bonds between adjacent nucleotides, creating the sugar-phosphate backbone.

Question 17

What is the final result of DNA replication?

Answer 17

Two identical DNA molecules are formed, each with one parental strand and one newly synthesized strand, preserving the genetic sequence.

Question 18

What does it mean that DNA strands are “antiparallel”?

Answer 18

DNA strands run in opposite directions: one is oriented 5’ to 3’, and the other 3’ to 5’. This orientation affects the way replication occurs.

Question 19

Why does replication occur differently on the leading and lagging strands?

Answer 19

DNA polymerase can only add nucleotides in the 5’ to 3’ direction. On the leading strand, replication is continuous, while on the lagging strand, it is discontinuous.

Question 20

How is the lagging strand replicated?

Answer 20

The lagging strand is synthesized in short fragments, which are later joined by DNA ligase to form a continuous strand.

Question 21

What is the role of DNA ligase in replication?

Answer 21

DNA ligase joins Okazaki fragments by forming phosphodiester bonds between them, completing the sugar-phosphate backbone.

Question 22

Why is DNA replication described as semi-conservative?

Answer 22

Each new DNA molecule contains one original (parental) strand and one new strand, conserving half of the original molecule.

Question 23

How does DNA replication ensure high accuracy?

Answer 23

Complementary base pairing rules and the proofreading ability of DNA polymerase minimize errors during replication.

Question 24

What is a template strand?

Answer 24

The original DNA strand used as a guide to synthesize the complementary strand.

Question 25

What are hydrogen bonds, and how do they function in DNA replication?

Answer 25

Weak bonds between complementary bases (A-T: 2 bonds, C-G: 3 bonds) that are broken during replication to expose the bases for pairing.

Question 26

What are phosphodiester bonds?

Answer 26

Covalent bonds linking the sugar of one nucleotide to the phosphate group of the next, forming the sugar-phosphate backbone.

Question 27

What is the role of free nucleotides in replication?

Answer 27

They pair with complementary bases on the template strand and form the new DNA strand when joined by phosphodiester bonds.

Question 28

What are replication errors, and how do they occur?

Answer 28

Replication errors occur when bases are not matched correctly during DNA replication, leading to an incorrect base sequence in the new strand. These errors are random, spontaneous, and result in mutations.

Question 29

What is a mutation?

Answer 29

A mutation is a permanent change in the sequence of bases in DNA, which may alter the function or expression of a gene.

Question 30

What is the role of DNA in genetics?

Answer 30

DNA contains the genetic instructions (genetic code) needed to synthesize proteins, which are the foundation of physical and biochemical traits in living organisms.

Question 31

How does DNA determine the proteins synthesized by an organism?

Answer 31

DNA encodes the sequence of amino acids in proteins. Proteins are formed by folding polypeptides. The sequence of amino acids determines a protein’s specific structure and function.

Question 32

How is genetic information stored in DNA?

Answer 32

Genetic information is stored in a triplet code, where each codon (a sequence of three bases) codes for one amino acid.

Question 33

What is a gene?

Answer 33

A gene is a section of DNA that contains the complete sequence of codons required to code for a specific protein.

Question 34

Why is the genetic code considered universal?

Answer 34

The genetic code is universal because the same codons code for the same amino acids in almost all organisms, although the sequence of codons differs between species.

Question 35

What does it mean that the genetic code is “degenerate”?

Answer 35

The genetic code is degenerate because there are 64 possible codons but only 20 amino acids. This means that most amino acids are coded for by multiple codons.

Question 36

Why is having a degenerate code beneficial?

Answer 36

It provides redundancy, reducing the effect of mutations, as changes in the third base of a codon often do not alter the amino acid.

Question 37

What is the role of a start codon?

Answer 37

The start codon signals the beginning of the protein-coding sequence in a gene. It codes for methionine (AUG) and ensures the reading frame starts correctly.

Question 38

What are stop codons, and what do they do?

Answer 38

Stop codons (UAA, UAG, UGA) do not code for any amino acid. They signal the end of the protein-coding sequence, terminating translation.

Question 39

What are the three stop codons?

Answer 39

UAA UAG UGA

Question 40

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

Answer 40

The genetic code is non-overlapping because each base is read only once, in groups of three, ensuring codons are read sequentially without overlap.

Question 41

Why is it important that the genetic code is read “in frame”?

Answer 41

Reading the code in frame (starting from the first base of the codon) ensures that the correct amino acid sequence is produced. A shift in the reading frame (frameshift mutation) can result in a completely different and non-functional protein.