topic 1B: more biological molecules (nucleic acids, ATP, water + inorganic ions) 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
what are both DNA AND RNA polymers of?
both DNA and RNA are polymers of nucleotides
definition of nucleotide
a nucleotide is a type of biological molecule, made from a pentose sugar (sugar with 5 carbon atoms), a nitrogen-containing organic base and a phosphate group
draw and label a DNA nucleotide
components of a DNA nucleotide
-deoxyribose
-phosphate group
-nitrogen containing organic bases adenine, cytosine, guanine or thymine
draw and label an RNA nucleotide
components of a RNA nucleotide
-ribose
-phosphate group
-nitrogen containing organic bases: adenine, cytosine, guanine or URACIL
condensation reaction between two nucleotides forms?
a condensation reaction between two nucleotides forms a phosphodiester bond
Describe the structure of DNA (5)
-double helix
-DNA is a polymer called polynucleotide made up of monomers of nucleotides joined together
-Each nucleotide is formed from a deoxyribose, a phosphate group and a nitrogen-containing organic base e.g. thymine, guamine, cytosine, adenine
-Phosphodiester bonds join adjacent nucleotides
-2 polynucleotide chains are held together by hydrogen bonds between specific complementary base pairs - adenine / thymine and cytosine / guanine
Describe the structure of (messenger) RNA (4)
-a single helix
-RNA is a polymer called polynucleotide made up of monomers of nucleotides joined together
-Each nucleotide is formed from ribose, a phosphate group and a nitrogen-containing organic base e.g.- URACIL, adenine, cytosine, guanine
-phosphodiester bonds join adjacent nucleotides
compare and contrast the structure of DNA and (messenger) RNA (5) UPTO MOCK
-DNA’s pentose sugar is deoxyribose whereas RNA’s Pentose sugar is ribose
-DNA Has the base thymine whereas RNA has the base uracil
-DNA is Double stranded / double helix whereas RNA is Single stranded / single helix
- DNA is Long (many nucleotides) whereas RNA is Shorter (fewer nucleotides)
-DNA Has hydrogen bonds / base pairing whereas RNA does not
Suggest how the structure of DNA relates to its functions (7)
REPLICATE
-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
STABLE MOLECULE
-Many hydrogen bonds between bases → stable / strong molecule
-Double helix with sugar phosphate backbone → protects bases / hydrogen bonds
STORAGE/COMPACT
-Long molecule → store lots of genetic information (that codes for polypeptides)
-Double helix (coiled) allows DNA to fit into nucelus → compact
Why did many scientists initially doubt that DNA carried the genetic code?
The relative simplicity of DNA - chemically simple molecule with few components
definition of Semi-conservative
- each new DNA molecule consists of one template (original) strand and one new strand
Why is semi-conservative replication important?
Ensures genetic continuity between generations of cells
process of semi conservative replication of DNA
- the enzyme DNA helicase BREAKS hydrogen bonds between complementary bases in the two polynucleotide strands, unwinding the double helix to form two strands
- Both strands act as TEMPLATES for new strands
- Free-floating DNA nucleotides are attracted to their complementary exposed bases and join by specific COMPLEMENTARY BASE PAIRING
- Hydrogen bonds form between the bases on the original and new strands (adenine-thymine and guanine-cytosine)
- DNA polymerase joins adjacent nucleotides on new strand by CONDENSATION reactions
- Forming phosphodiester bonds - each new DNA molecule contains one strand from the ORIGINAL DNA molecule and one new 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
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)
draw + describe structure of ATP
ATP (adenosine triphosphate) is a nucleotide derivative (modified nucleotide) and is formed from a molecule of ribose bound to a molecule of adenine (base) and 3 phosphate groups
Describe how ATP is hydrolysed
RELEASES ENERGY
-hydrolysis reaction of ATP to ADP and an inorganic phosphate group, using a water molecule catalysed by the enzyme ATP hydrolase
ATP ( + water ) —> ADP (adenosine diphosphate) + Pi (inorganic phosphate)
Give two ways in which the hydrolysis of ATP is used in cells
-the hydrolysis of ATP can provide energy for reactions and processes within cells (RELEASES ENERGY) eg. active transport, protein synthesis
-the Inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate (KEY: add phosphate to other substances, making them more reactive)
Describe how ATP is resynthesised in cells
ENERGY USED
-ATP is resynthesised by the condensation reaction of ADP and Pi, removing a water molecule
-this reaction is catalysed by the enzyme ATP synthase during photosynthesis and respiration
-ADP +Pi —> ATP (+water)
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
-can be rapidly resynthesised
water
Water is a major component of cells - it has several properties
Explain 5 properties of water that are important in biology
-METABOLITE: in many metabolic reactions, including used in condensation/ hydrolysis/ photosynthesis/ respiration
-SOLVENT (can dissolve solutes):
-allows metabolic reactions to occur (faster in solution)
-allows transport of substances e.g. nitrates in xylem, urea in blood
-RELATIVELY HIGH SPECIFIC HEAT CAPACITY: BUFFERS changes in temperature, as it can gain/ lose alot of heat/ energy without changing temperature
-good habitat for aquatic organisms as temperature is more stable than land
-helps organisms maintain a constant internal body temperature
-RELATIVELY LARGE LATENT HEAT OF VAPORISATION:
-allows effective cooling with little loss of water by evaporation of a small volume
-so helps organisms maintain a constant internal body temperature
-STRONG COHESION BETWEEN WATER MOLECULES:
-supports columns of water in tube-like transport cells of plants e.g. transpiration stream through xylem in plants
-produces surface tension where water meets air, supporting small organisms (to walk on water)
Explain how hydrogen bonds occur between water molecules
-water is a POLAR molecule
-slightly(delta) negatively charged oxygen attracts slightly positively charged hydrogen atoms of other water molecules
Where are inorganic ions found in the body?
In solution in cytoplasm and body fluid of organisms, some in high concentrations and others in very low concentrations
Describe the role of hydrogen ions
-H+
-MAINTAINS PH LEVELS in the body
-high concentration of hydrogen ions, the lower the pH and the more acidic
-pH affects enzyme-controlled reactions as it can cause enzymes to denature
describe the role of iron ions
-FE3+
-Component of haem group of haemoglobin
-Allowing oxygen to bind / associate for transport as oxyhaemoglobin
describe the role of sodium ions
-Na+
-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 phosphate 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
