1.5/1.6 Nucleic Acid and ATP Flashcards
Describe the basic functions of DNA and RNA in all living cells
DNA-Holds genetic information which codes for polypeptides (proteins)
RNA-Transfers genetic information from DNA to ribosomes
Name the two types of molecule from which a ribosome is made
RNA and proteins
Describe the differences between a DNA nucleotide and an RNA nucleotide
DNA nucleotide :
-Pentose sugar is deoxyribose
-Base can be thymine
RNA nucleotide:
-Pentose sugar is ribose
-Base can be uracil
Describe how nucleotides join together to form polynucleotides
● Condensation reactions, removing water molecules
● Between phosphate group of one nucleotide and deoxyribose / ribose of another
● Forming phosphodiester bonds
Why did many scientists initially doubt that DNA carried the genetic code?
The relative simplicity of DNA - chemically simple molecule with few components
Describe the structure of DNA
● Polymer of nucleotides (polynucleotide)
● Each nucleotide formed from deoxyribose, a phosphate group and a nitrogen-containing organic base
● Phosphodiester bonds join adjacent nucleotides
● 2 polynucleotide chains held together by hydrogen bonds
● Between specific complementary base pairs - adenine / thymine and cytosine / guanine
● Double helix
Describe the structure of (messenger) RNA
● Polymer of nucleotides (polynucleotide)
● Each nucleotide formed from ribose, a phosphate
group and a nitrogen-containing organic base
● Bases - uracil, adenine, cytosine, guanine
● Phosphodiester bonds join adjacent nucleotides
● Single helix
Compare and contrast the structure of DNA and (messenger) RNA
Pentose sugar is deoxyribose (DNA)
Pentose sugar is ribose (RNA)
Has the base thymine (DNA)
Has the base uracil (RNA)
Double stranded / double helix (DNA)
Single stranded / single helix (RNA)
Long (many nucleotides) (DNA)
Shorter (fewer nucleotides) (RNA)
Has hydrogen bonds / base pairing (DNA)
Does not (RNA)
Suggest how the structure of DNA relates to its functions
● Two strands → both can act as templates for semi-conservative replication
● Hydrogen bonds between bases are weak → strands can be separated for replication
● Complementary base pairing → accurate replication
● Many hydrogen bonds between bases → stable / strong molecule
● Double helix with sugar phosphate backbone → protects bases / hydrogen bonds
● Long molecule → store lots of genetic information (that codes for polypeptides)
● Double helix (coiled) → compact
Suggest how you can use incomplete information about the frequency of bases on DNA strands to find the frequency of other bases
- % of adenine in strand 1 = % of thymine in strand 2 (and vice versa) 2. % of guanine in strand 1 = % of cytosine in strand 2 (and vice versa) Because of specific complementary base pairing between 2 strands
Why is semi-conservative replication important?
Ensures genetic continuity between generations of cells
Describe the process of semi-conservative DNA replication
- DNA helicase breaks hydrogen bonds between complementary bases, unwinding the double helix
- Both strands act as templates
- Free DNA nucleotides attracted to exposed bases and join by specific complementary base pairing
- Hydrogen bonds form between adenine-thymine and guanine-cytosine
- DNA polymerase joins adjacent nucleotides on new strand by condensation reactions
- Forming phosphodiester bonds
Use your knowledge of enzyme action to suggest why DNA polymerase moves in opposite directions along DNA strands
● DNA has antiparallel strands
● So shapes / arrangements of nucleotides on two ends are different
● DNA polymerase is an enzyme with a specific shaped active site
● So can only bind to substrate with complementary shape (phosphate end of developing strand)
Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication
Watson and Crick
Describe the work of Meselson and Stahl in validating the Watson-Crick model of semi-conservative DNA replication
- Bacteria grown in medium containing heavy nitrogen (15N) so
nitrogen is incorporated into DNA bases
○ DNA extracted & centrifuged → settles near bottom, as all
DNA molecules contain 2 ‘heavy’ strands - Bacteria transferred to medium containing light nitrogen (14N)
and allowed to divide once
○ DNA extracted & centrifuged → settles in middle, as all DNA
molecules contain 1 original ‘heavy’ and 1 new ‘light’ strand - Bacteria in light nitrogen (14N) allowed to divide again
○ DNA extracted & centrifuged → half settles in middle, as
contains 1 original ‘heavy’ and 1 new ‘light’ strand; half settles
near top, as contains 2 ‘light’ strands
What is ATP?
Adenosine triphosphate
Describe the structure of ATP
● Ribose bound to a molecule of adenine
(base) and 3 phosphate groups
● Nucleotide derivative (modified nucleotide)
Describe how ATP is broken down
● ATP (+ water) → ADP (adenosine diphosphate) + Pi (inorganic phosphate)
● Hydrolysis reaction, using a water molecule
● Catalysed by ATP hydrolase (enzyme)
Give two ways in which the hydrolysis of ATP is used in cells
● Coupled to energy requiring reactions within cells (releases energy)
○ eg. active transport, protein synthesis
● Inorganic phosphate released can be used to phosphorylate
(add phosphate to) other compounds, making them more reactive
Suggest how the properties of ATP make it a suitable immediate source of energy for cells
● Releases energy in (relatively) small amounts / little energy lost as heat
● Single reaction / one bond hydrolysed to release energy (so immediate release)
● Cannot pass out of cell
