DNA replication, transcription and translation

How many hydrogen bonds between adenine and thymine?

2

What is a codon?

A sequence of nucleotides on mRNA that corresponds to an amino acid

Phosphidiester bond

Always formed between phosphate group attached to 5' of the sugar, and the OH group attached to the 3'

Definition and examples of pyrimidines

Bases with 1 ring in structure. Cytosine, thymine and uracil.

Definition and examples of purines

Bases with 2 rings in structure. Adenine, guanine.

Name the enzyme that separates the two strands of the DNA double helix during replication.

DNA Helicase

Which enzyme is responsible for joining together the nucleotides of the new DNA strand during DNA replication?

DNA Polymerase

What is involved in both replication and transcription?

DNA and RNA Explanation: Replication is when the DNA in a cell is doubled in quantity. Transcription is when the DNA is transcribed into mRNA. So DNA is involved in both. It should be noted that RNA is also involved in both.

Which enzyme is responsible for unwinding the DNA double helix in preparation for DNA replication?

DNA helicase

Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?

DNA in both daughter cells would be radioactive. Explanation when the DNA is replicated the two new DNA molecules contain both an old and a new strand of DNA. So both daughter cells would have a double-stranded DNA molecule where one strand, the old one, is not radioactive but the anti-parallel strand, which was newly formed during the replication, would contain radioactive thymine. So both daughter cells would be radioactive, therefore option #4 is the correct answer.

What are the components of a DNA nucleotide?

Deoxyribose, a phosphate and one of the bases: adenine, cytosine, guanine or thymine.

When does DNA replication occur?

During the S phase of interphase

Name the type of bond that holds the two DNA strands together in the DNA molecule.

Hydrogen Bonds between the nitrogenous strands need to be weak so that separation of the two stands is easy

How would the following DNA sequence, ACGTTGCATGGCA, be transcribed?

UGCAACGUACCGU Because it is transcribed and not replicated, Uracil would be there and not thymine, as this is RNA.

How many hydrogen bonds between guanine and cytosine?

3

If 15% of a sample of DNA is thymine, what percentage of the DNA is guanine?

35% Explanation: If there is 15% thymine, then there must be 15% adenine. So 100 - 30 = 70% is left which means that there must be 35% guanine and 35% cytosine.

If a DNA sample were composed of 10% thymine, what would be the percentage of guanine?

40 Explanation: If a DNA sample contains 10 % thymine that means there would have to be 10% adenine as well, as thymine pairs with adenine. That leaves 80% for cytosine and guanine combined; so the correct answer is half of 80 (which is 40)

Which are the correct directions of the following processes: Replication Transcription Translation

5' to 3' 5' to 3' 5' to 3' These processes always proceed in a 5' to 3' direction.

If a polypeptide consists of 240 amino acids, what is the minimum number of nucleotides needed on the sense strand of a gene to code for it?

720 Explanation: Each amino acid is coded by a 3 DNA nucleotides (a codon). If the polypeptide has 240 amino acids it requires 240 codons. So the correct answer is 3 × 240 = 720 nucleotides.

Why would base ratios between DNA and RNA differ?

DNA is made entirely of double helix but RNA is not. Explanation: DNA is a double helix with complementary base pairing. So the percentage A and T should be equal because they pair up (same is true for G and C). RNA however is usually single stranded so the percentages do not need to match.

Which of the following happens the earliest during DNA replication?

Free nucleotides base pair to original polynucleotide. Free nucleotides that base pair to original polynucleotide comes first of the choices provided, thus #1 should be picked as the correct answer. This is a stage that exists between the action of the helicase unwinding the double helix and the joining of the sugar-phosphate backbone by means of DNA polymerase.

Which of the following happens the earliest during DNA replication?

Free nucleotides base pair to original polynucleotide. Free nucleotides that base pair to original polynucleotide comes first of the choices provided. This is a stage that exists between the action of the helicase unwinding the double helix and the joining of the sugar-phosphate backbone by means of DNA polymerase.

What occurs during the initial step of DNA replication?

Helicase separates the two DNA strands. Explanation: DNA replication is semi-conservative. The first step in the process is the separation of the DNA double helix into two template strands.

What type of bond connects two DNA strands?

Hydrogen bonds Explanation: Hydrogen bonds form between a purine nitrogenous base on one strand and a pyrimidine nitrogenous base on the other. This phenomenon is known as complementary base pairing.

Which molecule is found in both DNA and RNA?

Phosphate Ribose sugar and uracil are only found in RNA whilst amino acids are found in neither DNA or RNA.

What are the three main components of a DNA nucleotide?

Phosphate, Deoxyribose sugar, Nitrogenous Base

Which of the enzyme is responsible for uncoiling and separating the DNA strands during transcription?

RNA Polymerase

Which of the following enzymes is responsible for uncoiling and separating the DNA strands during transcription?

RNA Polymerase its important to read the question correctly- in translation it would be DNA helicase, but in translation it is RNA polymerase which uncoils the DNA.

Which enzyme is responsible for uncoiling and separating the DNA strands during transcription?

RNA polymerase Explanation: RNA polymerase binds to the promoter of the antisense strand and unwinds a section of the DNA molecule during transcription. The other enzymes are all involved in DNA replication.

In a DNA deoxyribose sugar of a single nucleotide, which carbon is connected to the base?

The 1st carbon The 5th carbon makes up the 5' end and the 3rd carbon makes up the 3' end of a nucleotide. The carbons are counted clockwise starting from the carbon attached to the base and finishing on the carbon attached to the phosphate.

In a DNA deoxyribose sugar of a single nucleotide, which carbon is connected to the base?

The first carbon Explanation: The 5th carbon makes up the 5' end and the 3rd carbon makes up the 3' end of a nucleotide. The carbons are counted clockwise starting from the carbon attached to the base and finishing on the carbon attached to the phosphate.

Which carbon(s) in a DNA deoxyribose sugar of a single nucleotide is/are part of the link to an adjacent nucleotide?

The third and fifth carbon Explanation: The 5th carbon makes up the 5' end and the 3rd carbon makes up the 3' end of a nucleotide. The carbons are counted clockwise starting from the carbon attached to the base and finishing on the carbon attached to the phosphate.

How would the following DNA sequence, ACGTTGCATGGCA, be transcribed?

UGCAACGUACCGU Explanation: The DNA functions as a template and the single-stranded mRNA molecule that is made follows the complementary base pairing rules of DNA with one exception. Remember in DNA G(uanine) always pairs with C(ytosine) and A(denine) pairs with T(hymine). However, T replaces U(racil) in RNA, so in a mRNA molecule whenever there is an A in the DNA template a U will appear in the newly formed mRNA

Name the sugar present in DNA nucleotides.

deoxyribose

What occurs during translation?

tRNA with an attached amino acid binds to a complementary codon on mRNA. Explanation: During translation, the tRNA molecules attach to the complementary codons on mRNA and hold amino acids close together to allow peptide bonds to form. The peptide bond can only form when two tRNA molecules hold their amino acids close to each other.