DNA Flashcards
Describe the structure of DNA.
- Polymer of nucleotides;
- Each nucleotide formed from deoxyribose, a phosphate (group) and
an organic/nitrogenous base; - Phosphodiester bonds (between nucleotides);
- Double helix/2 strands held by hydrogen bonds;
- (Hydrogen bonds/pairing) between adenine, thymine and
cytosine, guanine;
Describe how a phosphodiester bond is formed between two nucleotides
within a DNA molecule.
- Condensation (reaction)/loss of water;
- (Between) phosphate and deoxyribose;
- (Catalysed by) DNA polymerase;
In the process of semi-conservative DNA replication, the two strands within
a DNA molecule are separated.
Each then acts as a template for the
formation of a new complementary strand.
Describe how the separation of strands occurs.
Breaks hydrogen bonds between base pairs/ AT and
GC/complementary bases
OR
Breaks hydrogen bonds between polynucleotide strands;
Name the protein associated with DNA in a chromosome.
Histone
Describe the role of DNA polymerase in the semi-conservative replication
of DNA.
- Joins (adjacent DNA) nucleotides;
- (Catalyses) condensation (reactions);
- (Catalyses formation of) phosphodiester bonds (between adjacent
nucleotides);
Name the two scientists who proposed models of the chemical structure of
DNA and of DNA replication.
Watson and Crick
Name the enzyme used in this DNA replication.
DNA polymerase
Use your knowledge of semi-conservative replication of DNA to suggest:
- the role of the single-stranded DNA fragments
- the role of the DNA nucleotides.
Role of single-stranded DNA fragments:
1.Template;
2. Determines order of nucleotides/bases;
Role of DNA nucleotides:
3. Forms complementary pairs / A – T, G - C
OR
Forms complementary (DNA) strand;
Give two features of DNA and explain how each one is important in the
semi-conservative replication of DNA.
- Weak / easily broken hydrogen bonds between bases allow two
strands to separate / unzip; - Two strands, so both can act as templates;
- Complementary base pairing allows accurate replication;
Describe the role of two named enzymes in the process of semi
conservative replication of DNA.
- (DNA) helicase causes breaking of hydrogen/H bonds (between DNA
strands); - DNA polymerase joins the (DNA) nucleotides;
- Forming phosphodiester bonds;
Adenosine triphosphate (ATP) is a nucleotide derivative.
Contrast the structures of ATP and a nucleotide found in DNA to give two
differences.
ATP has ribose and DNA nucleotide has
deoxyribose;
ATP has 3 phosphate (groups) and DNA
nucleotide has 1 phosphate (group);
ATP – base always adenine and in DNA
nucleotide base can be different / varies;
During replication, the two DNA strands separate and each acts as a
template for the production of a new strand. As new DNA strands are
produced, nucleotides can only be added in the 5’ to 3’ direction.
Use the figure in part (a) and your knowledge of enzyme action and DNA
replication to explain why new nucleotides can only be added in a 5’ to 3’
direction.
Reference to DNA polymerase;
(Which is) specific;
Only complementary with / binds to 5’ end (of strand);
Shapes of 5’ end and 3’ end are different
Describe the chemical reactions involved in the conversion of polymers to
monomers and monomers to polymers.
Give two named examples of polymers and their associated monomers to
illustrate your answer.
A condensation reaction joins monomers together and forms a (chemical) bond and releases water;
A hydrolysis reaction breaks a (chemical) bond between monomers and uses water;
A suitable example of polymers and the monomers from which
they are made;
3. and 4. Polymers must contain many monomers.
3. and 4: suitable examples include
* amino acid and polypeptide, protein, enzyme, antibody or specific
example
* nucleotide and polynucleotide, DNA or RNA
* Alpha glucose and starch/glycogen
* Beta glucose and cellulose.
