1.5-1.8 Flashcards
Describe the basic functions of DNA and RNA:
DNA: holds genetic info which codes for polypeptides
RNA: transfers genetic info 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:
Pentose sugar is deoxyribose in DNA but ribose in RNA
Base can be thymine in DNA but uracil in RNA
How do nucleotides join together to form polynucleotides?
Condensation reaction, 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 with few components
Describe the structure of DNA:
Polymer of nucleotides
Each nucleotide formed from deoxyribose, phosphate group and a nitrogen-containing organic base
2 polynucleotide chains held together by H bonds
Between specific complementary base pairs- adenine/thymine and cytosine/guanine
Double helix
Describe the structure of mRNA:
Polymer of nucleotides
Each nucleotide formed from ribose, phosphate group and nitrogenous base
Bases- uracil, adenine, cytosine and guanine
Phosphodiester bonds join adjacent nucleotides
Single helix
Compare and contrast the structure of DNA and mRNA:
Deoxyribose v ribose
Thymine v uracil
Double stranded v single stranded
Long v shorter
H bonds/base pairing v doesn’t
How does the structure of DNA link to its functions?
Two strands so both can act as templates for semi-conservative replication
H bonds between bases are weak- strands can be separated for replication
Complementary base pairing- accurate replication
Many H bonds- stable/strong molecule
Long molecule- contains lots of genetic info
Double helix- compact
What is semi conservative replication and why is it important?
Each new DNA molecule consists of one original/template strand and one new strand
Ensures genetic continuity between generations of cells
Describe the process of semi-conservative replicication:
- DNA helicase breaks H 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
- H bonds form between adenine-thymine and guanine-cytosine
- DNA polymerase joins adjacent nucleotides on new strand by condensation reactions
- Forming phosphodiester bonds
Why does DNA polymerase move 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 DNA replication:
Watson and Crick
Describe the work of Meselson and Stahl in validating the Watson-Crick model of semi-conservative replication:
- Bacteria grown in medium containing heavy nitrogen (15N) and nitrogen is incorporated into DNA bases
-DNA is extracted and centrifuged so settles near bottom, as all DNA molecule contains 2 heavy strands - Bacteria transferred to medium containing light nitrogen (14N) and allowed to divide once
-DNA extracted and centrifuged, so settles in middle as all DNA molecules contain 1 original and 1 new ‘light strand’ - Bacteria in light nitrogen allowed to divide again
-DNA extracted and centrifuged so half settles in middle as contains 1 original heavy strand and 1 new light strand, and 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 and 3 phosphates
Nucleotide derivative
Describe how ATP is broken down:
ATP (+water) –> ADP + Pi
Hydrolysis reaction, using a water molecule
Catalysed by ATP hydrolase
Give two ways in which the hydrolysis of ATP is used in cells:
Coupled to energy requiring reactions within cells (releases/provides energy)
Inorganic phosphate can be used to phosphorylate other compounds, making them more reactive
Describe how ATP is resynthesised in cells:
ADP + Pi –> ATP (+water)
Condensation reaction, removing a water molecule
Catalysed by ATP synthase
During respiration and photosynthesis
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) so immediate energy release
Cannot pass out of cell
How does H bonds occur between water molecules?
Water is a polar molecule
Slightly negative oxygen atoms attract slightly positive hydrogen atoms of other water molecules
Why is water being a metabolite important in biology?
Used in condensation/hydrolysis/photosynthesis/respiration
Why is water being a solvent important in biology?
Allows metabolic reactions to occur
Allows transport of substances
Why is the high specific heat capacity of water important in biology?
Buffers changes in temperature
As can gain/lose a lot of heat/energy without changing temp
Good habitat for aquatic organisms as temp more stable than land
Helps organisms maintain a constant internal body temp
Why is the high latent het of vaporisation of water important in biology?
Allows effective cooling via evaporation of a small volume
So helps organisms maintain a constant internal body temperature
Why is the strong cohesion between water molecules important in biology?
Supports columns of water
Produces surface tension, supporting small organisms
Where are inorganic ions found?
In solution in cytoplasm and body fluid, some in high conc. others in very low conc.
Describe the role of H+ ions:
Maintain pH levels in the body
- High conc= acidic/low pH
Affects enzyme rate of reaction as can cause enzymes to denature
Describe the role of Fe2+ iona
Component of haem group of haemoglobin
Allows oxygen to bind/associate for transport as oxyhaemoglobin
Describe the role of Na+ ions:
Involved in co transport of glucose/amino acids into cells
Involved in action potentials in neurons
Affects water potential of cells/osmosis
Describe the role of PO4 3- ions:
Component of nucleotides allowing phosphodiester bonds to form in DNA/RNA
Component of ATP, allowing energy release
Phosphorylates other compounds making them more reactive
Hydrophilic part of phospholipids allowing a bilayer to form
