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38 Cards in this Set

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What is the function of DNA?
Store genetic information; all the instructions and organism needs to grow and develop.
What is the main function of RNA?
Transfer genetic information from the DNA to the ribosomes.
What are nucleotides?
Monomers that join together to form DNA or RNA (polymers).
What is a nucleotide made from?
A pentose sugar; a nitrogen organic base; a phosphate group.
Compare the nucleotides of DNA and RNA?

DNA contains deoxyribose sugar; RNA contains ribose sugar.




DNA contains the bases A, T, C and G; RNA replaces T with U (uracil).




DNA is made of two polynucleotide strands; RNA is only single stranded.

How do nucleotides (monomers) join together to form DNA or RNA (polymers)?
Condensation reactions between the phosphate group of one nucleotide with sugar of another.
What is the chain of sugars and phosphate known as?
The sugar-phosphate backbone.
Outline the structure of a DNA molecule?

Two DNA polynucleotides joined together; held together hydrogen bonding between bases.




A pairs with T and C pairs with G; complementary base pairing.




Two antiparallel polynucleotide strands twist to form double helix.

How does DNA replicate?
DNA replicates semi-conservatively.
Why is DNA replication described as semi-conservative?
One of the two strands in each new DNA molecule is from the original DNA.
Outline the process of semi-conservative replication?

DNA helicase breaks hydrogen bonds between complementary base pairs; helix unwinds.




Each original strand used as template; complementary base pairing free-floating DNA nucleotides attracted exposed bases on original strand.




DNA polymerase joins the nucleotides; hydrogen bonds form between complementary bases.




Each new DNA molecule contains one original and one new strand of DNA.


Why can DNA polymerase only add nucleotides to new strand at 3' (prime) end?
The active site of DNA polymerase is only complementary to the 3' (prime) end of newly forming DNA strand.
\Who provided evidence for semi-conservative replication?
Meselson and Stahl.
What did the experiment involve?
Two isotopes of nitrogen; light nitrogen (N14) and heavy nitrogen (N15).
Give the structure of water molecules?


H2O; one atom of oxygen, two atoms of hydrogen.

Why is water a polar molecule?
It has a partial negative charge on one side (O-) and a partial positive charge on the other side (H+).

The slightly negatively charged oxygen atoms attract what?

The slightly positively charged hydrogen atoms.
What is this attraction called?
Hydrogen bonding.
Why is water an important metabolite; why is this useful?

Many metabolic reactions involve condensation and hydrolysis reactions.




eg. Energy released from ATP by hydrolysis of ATP to ADP + Pi.

Water has a high latent heat of vaporisation; what does this mean and why is it useful?

It takes a lot of energy to break hydrogen bonds between water molecules; a lot of energy is used up when it evaporates.




eg. Humans sweat to cool down without losing too much water.

Water can buffer (resist) changes in temperature; why is this useful?

Hydrogen bonds can absorb a lot of energy so water has high specific heat capacity.






eg. Water inside organisms remains fairly stable temperature - helps to maintain constant body temperature.

Water is a good solvent; explain why and how this is useful?

Lot of important substances in metabolic reactions; ionic.




Water is polar; positive end attracted to negative ion and vice versa - ions totally surrounded by water; they'll dissolve.

There is strong cohesion between water molecules; why is this important?

Water molecules cohesive as they are polar; strong cohesion helps water to flow making it great for transporting substances.




eg. Water travels in columns up xylem.

What does strong cohesion also provide?

High surface tension.
What molecule is immediate source of energy in a cell?

Adenosine Triphosphate; ATP.
How is ATP made from respiration?
In respiration, energy released from glucose to make ATP.
What is the structure of ATP?

Nucleotide base - adenine; ribose sugar; three phosphate groups.
How is the energy stored in ATP?
In high energy bonds between the phosphate groups.
When energy is needed by the cell, what happens to ATP?
It is hydrolysed into ADP + Pi (inorganic phosphate); phosphate bond broken and energy is released.
ATP can be re-synthesised; how?
By a condensation reaction between ADP and Pi.

When does this condensation reaction occur?

During respiration and photosynthesis; catalysed by ATP synthase.
What is an ion?
An atom with an electrical charge.

What is an ion with a positive charge called?


A cation.

What is an ion with a negative charge called?

An anion.
Iron ions (Fe2+) are an important part of which molecule?

Haemoglobin; Fe2+ binds to the oxygen - temporarily becomes Fe3+ until oxygen released.
Why are hydrogen ions (H+) important?
H+ ions determine pH; the more H+ ions the lower the pH and more acidic.
Why are sodium ions (Na+) important?
Transport glucose and amino acids across cell membranes.

Why are phosphate ions (PO4[3-]) important in DNA/RNA and ATP?

In DNA/RNA; allows nucleotides join to form polynucleotide chains.




In ATP; bonds between phosphates that store energy.