Nucleic Acids, ATP, Water & Inorganic Ions Flashcards
What is a polynucleotide
formed when many nucleotides link to form a long chain, by condensation
Nucleotides
A Nucleotide is the monomer of a nucleic acid. It is made up from 3 components.
1) Phosphate group
2) Nitrogen-containing organic base
3) Deoxyribose or Ribose sugar
DNA vs RNA
DNA:
Adenine, Thymine (2 H bonds)
Cytosine, Guanine (3 H bonds)
3 bases= triplet
RNA:
Adenine, Uracil
Cytosine, Guanine
3 bases= codon
Polynucleotide formation
2 strands of DNA run in opposite directions, which means they are antiparallel.
Each end of the molecule is labelled with a 5’-end and a 3’-end
Describe the structure of DNA
- Sugar-phosphate backbone so provides strength
- Long/large molecule so can store lots of information;
- Helical so compact;
- Base sequence allows information to be stored
- Double stranded so strands can act as templates;
- Complementary base pairing so accurate replication
- (Weak) hydrogen bonds for strand separation;
- Many weak hydrogen bonds so stable
Describe Semi-conservative replication
- DNA helicase breaks H bonds
- Strands separate
- Both strands act as a template
- (Free) nucleotides attach;
- Complementary base pairing due to H bonds forming between bases
- DNA polymerase joins nucleotides forming phosphodiester bonds by condensation;
- New DNA molecules contain one old strand and one new strand;
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
Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication.
Crick and Watson
The Meselson Stahl Experiment
Grow bacteria in nitrogen heavy medium.
Transfer some bacteria to nitrogen light medium; bacterial growth continues
Take samples after 0, 20 and 40 minutes
Before bacteria reproduce for first time in light medium, all DNA is heavy
After 2 generations, DNA was intermediate
ATP structure
consists of a nitrogenous organic (adenine) base, ribose sugar and three phosphate groups
Uses of ATP
Provides energy for:
Active transport;
Muscle contraction;
Protein synthesis.
Phosphorylation:
Of molecules to lower Ea
make substrates more reactive
ATP → ADP + Pi
- energy released (-30.6kJ)
- ATP hydrolase removes terminal phosphate
- hydrolysis reaction
ADP + Pi → ATP
- energy used (+30.6kJ)
- ATP synthase adds terminal inorganic phosphate
- condensation reaction
- creates high energy bond
Describe how an enzyme can be phosphorylated.
- Attachment of (inorganic) phosphate
- Released from hydrolysis of ATP
ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use.
- Little energy is lost as heat
- Releases energy instantaneously
- Phosphorylates other compounds, making them more reactive
- Can be rapidly re-synthesised
- Is not lost from cells
Describe how ATP is resynthesized in cells
- ADP + Pi
- By ATP synthase
- In respiration
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 and DNA nucleotide has 1 phosphate
- ATP- base always adenine and in DNA nucleotide base can be different
Explain five properties that make water important for organisms.
- A metabolite in condensation
- A solvent so (metabolic) reactions can occur
- High heat capacity so buffers changes in temperature;
- Large latent heat of vaporisation so provides a cooling effect
- Cohesion (between water molecules) so supports columns of water (in plants);
- Cohesion (between water molecules) so produces surface tension supporting (small) organisms
Suggest why water becomes lighter as it expands
- Density = mass ÷ volume;
- Ice has same mass of water but greater volume
Suggest one biological advantage of this property of water.
- Ice is colder than water;
- (Being lighter than water) ice floats on water;
Scientists looking for extra-terrestrial life are looking for planets with evidence of free water. Explain why water is considered so important for life to occur. (6)
- Life (thought to have) evolved in water;
- Water provides support (for bodies of organisms);
- Water a major component of cytoplasm;
- Water is a universal solvent
- Water is a metabolite in many cell reactions;
- Water stabilises temperature;
- Water important in cooling internal temperature (of organisms);
Describe the roles of iron ions, sodium ions, and phosphate ions in cells.
Iron ions
1. Haemoglobin binds with oxygen
Sodium ions
2. Co-transport of glucose/amino acids (into cells);
3. (Because) sodium moved out by active transport
4. Creates a diffusion gradient;
5. Affects osmosis
Phosphate ions
6. Affects osmosis
7. Joins nucleotides in backbone of DNA
8. Used to produce ATP;
9. Phosphorylates other compounds making them more reactive;
10. Hydrophilic part of phospholipid bilayer
