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DNA Structure

DNAReplication Biotech TranscriptionTranslation

What are the three components of a nucleotide?

Answer

•Sugar•Phosphate

•Nitrogen base

Name the nitrogen bases in DNA

Answer

•Thymine•Adenine•Guanine•Cytosine

Indicate the type and number of bonds that hold the DNA strands

together

Answer

•Hydrogen bonds•2 between adenine and thymine•3 between guanine and cytosine

If the percentage composition of adenine in a DNA molecule is 10%

then what are the percent compositions of the other 3 bases.

Answer

•Thymine = 10%•Guanine = 40 %•Cytosine = 40%

What specific types of bond attaches the nitrogen base to the sugar?The phosphate to the sugar?

Answer

Nitrogen base + sugar = glycosylPhosphate + sugar = phosphodiester

Note: Both are covalent bonds!

What enzyme unwinds DNA at the fork by breaking hydrogen bonds

between nitrogen bases?

Answer

helicase

What enzyme relieves stress further up the fork?

Answer

DNA gyrase

What enzyme binds complimentary bases and what direction does it

move? What has to be in place first before this enzyme can bind to the

template?

Answer

DNA polymerase III which moves in a 5′ to 3′ direction. An RNA primer laid down by

RNA primase must be in place first.

What are the names of the fragments of the sections on the lagging strand

and what enzyme joins these sections?

Answer

Okazaki fragments are joined by DNA ligase.

How does the fact that DNA replicates semi-conservatively

decrease the possibility of errors made during DNA replication?

You must first explain the term semi-conservatively.

Answer

Semi-conservative replication means that each parent strand serves as a template from which a copy can be made. This template serves as the

checkpoint when DNA polymerase I and III proofread the newly synthesized strand.

What molecular biology technique would be the most appropriate for

analyzing the size of DNA fragments?

Answer

Gel electrophoresis

What are three circumstances where one might want to amplify the

amount of DNA by PCR?

Answer

Studying fossil remainsDNA found at scene of crime

Early diagnosis of disease (HIV)

Observe the following DNA fingerprint and determine who

should remain a suspect.

Answer

JOHN

What does a restriction endonuclease do?

Answer

Recognizes and cuts DNA at a specific sequence.

How are recombinant bacteria differentiated from the original

bacteria?

Answer

Recombinant bacteria also received a marker gene (eg. Antibiotic

resistance) that allows them to be easily distinguished when culturing.

Does transcription require a primer?

Answer

No

What must be recognized to initiate transcription?

Answer

Promoter

What enzyme creates the mRNA strand and what direction does it

move?

Answer

RNA polymerase synthesizes mRNA in a 5′ to 3′ direction.

What is an intron?An exon?

Which is removed by what enzyme?

Answer

Introns = non-coding regions of mRNAExons = coding regions of mRNA

Spliceosomes remove introns

What modifications must be made to the ends of the mRNA transcript

before it can leave the nucleus and why must these occur?

Answer

Cap – methyl guanineTail – Poly A tail by poly A polymerase

To prevent degradation by enzymes in the cytoplasm

Where in the cell does translation occur?

Answer

Cytoplasm at the ribosomes

What is necessary to initiate translation? Indicate the specific

sequence of this initiator.

Answer

Start codon (AUG) on mRNA is recognized by the ribosome.

Differentiate between a codon and an anticodon.

Answer

Codon = 3 nucleotide bases on mRNA that code for one amino acid

Anticodon = 3 nitrogen bases on tRNA that are complimentary to the codon on mRNA.

What are the three types of RNA and what are their functions in

translation

Answer

Messenger RNA – brings copy of gene to be readRibosomal RNA – reads or translates mRNA copy

by exposing 3 bases at a timeTransfer RNA – brings in amino acids to form

polypeptide

Which is more harmful; a substitution or a deletion?