T1: Biological Molecules Flashcards
Define monomer. Give three examples.
- is a small , repeating unit from which larger molecules / polymers are made.
- monosaccharides
- amino acids
- nucleotides
Define polymer. Give three examples
molecules formed when many monomers join together
- polysaccharides
- proteins
- DNA/RNA
Describe a condensation reaction.
- A chemical bond forms between 2 molecules & a molecule of water is produced
Describe a hydrolysis reaction
- a water molecule is used to break a chemical bond between 2 molecules
Name the 3 (hexose) monosaccharides
- glucose
- fructose
- galactose
Name the type of bond formed when monosaccharides react.
- glycosidic bond
Name three disaccharides and what they consist of. Describe how they form.
draw the formation of glycosidic bond between 2 monosaccharides
- condensation reaction forms glycosidic bond between 2 monosaccharides
maltose: 2 glucose
sucrose: glucose + fructose
lactose: glucose + galactose
What is the difference between an alpha glucose and beta glucose molecule?
in beta glucose, hydroxyl group on carbon 1 is facing upwards
Describe the structure and function of starch
storage polymer of alpha glucose in plant cells
- insoluble= no osmotic effect on cells / does not affect water potential
- large= does not diffuse out of cells
made from amylose:
1,4 glycosidic bonds
- helical so compact
amylopectin:
- 1,4 & 1,6 glycosidic bonds
- branched= many terminal ends for hydrolysis into glucose
Describe the structure and functions of glycogen.
- main storage polymer of alpha glucose in animal cells
- 1,4 & 1,6 glycosidic bonds
- branched = many terminal ends for hydrolysis
- insoluble= no osmotic effect and does not diffuse out of cells
- compact
Describe how the structure of glycogen is related to its function. (4)
- it has a helix and branched structure and so is compact
- Branched so more ends for faster hydrolysis;
polymer of Glucose so provides respiratory substrate for energy (release); - Insoluble so does not affect water potential/osmosis
alternatives : - Polymer of glucose so easily hydrolysed
Describe and explain how the structure of cellulose relates to its function (4)
- 1,4 glycosidic bonds
- cellulose is made up of long unbranched straight chains of beta glucose
- which interact to form microfibrils
- the chains of b glucose are joined together by hydrogen bonds
- which provide strength in cell walls
Describe the test for identifying reducing sugars in a food sample
- add an equal volume of Benedict’s reagent to a sample
- heat the mixture in an electric water bath for 100°C
- POSITIVE RESULT: colour change from blue to orange & brick-red precipitate forms
Red / orange / yellow / green (colour); Reject Add HCl
Describe the Benedict’s test for non-reducing sugars
- negative result: Benedict’s reagent remains blue
- hydrolyse non-reducing sugars e.g. sucrose into their monomers by adding 1cm3 of HCl
- heat in a boiling water bath for 5 mins
- neutralise the mixture using sodium carbonate solution
- proceed with the Benedict’s test as usual
Describe the test for starch
- Add iodine solution
- Positive result: colour change from orange to blue-black
Describe how to test for lipids in a sample
- Dissolve solid samples in ethanol . alcohol
- THAN Add an equal volume of water and shake and mix
- Positive result: milky white emulsion forms
How do triglycerides form?
draw one
- ## condensation reaction between 1 molecule of glycerol and 3 fatty acids forms ester bonds.
Compare saturated and unsaturated fatty acids
saturated:
- contain only single bonds
- higher melting point = solid at room temp
- found in animal fats
unsaturated:
- contain C=C double bonds
- lower melting point liquid at room temp
Describe how a saturated fatty acid differs in molecular structure from an unsaturated fatty acid (2)
- absence of a double bond;
- in the (hydrocarbon) chain;
- unable to accept more hydrogen / saturated with hydrogen;
characteristics of triglycerides
- insoluble hydrocarbon chain so no effect on water potential of cells and used for waterproofing
- slow conductor of heat: thermal insulation
describe the structure and function of phospholipids
- Amphipathic molecule: glycerol backbone attached 2 hydrophobic fatty acid tails & 1 hydrophilic polar phosphate head,
- forms phospholipids bilayer in water = component of membranes
- tail can splay outwards = waterproofing
Compare phospholipids and triglycerides
give 4 similarities
- both have glycerol backbone
- both may be attached to a mixture of un/mono/poly saturated fatty acids
- both contain the elements C,H,O
- both formed by condensation reactions
Contrast phospholipids and triglycerides
p:
- 2 fatty acids & 1 phosphate group attached
- hydrophilic head & hydrophobic tail
- used primarily in membrane formation
t:
- 3 fatty acids attached
- entire molecule is hydrophobic
- used primarily as a storage molecule
Are phospholipids and triglyceride polymers?
- No, they are not made from a small repeating unit
- they are macromolecules
Draw the structure of a nucleotide
- a phosphate group attached to a pentose sugar attached to a nitrogen-containing base
search up diagram - check with answer
Name the pentose sugars in DNA & RNA
DNA: deoxribose
RNA: ribose
State the role of DNA in living cells
- contains genetic information
- which determines inherited characteristics = influences structure and function of organisms
How do polynucleotides form?
- phosphodiester bonds form
- as a result of a condensation reaction between nucleotides
- leads to sugar - phosphate backbone
Describe the structure of DNA (5)
- Polymer of nucleotides;
- Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
- Phosphodiester bonds (between nucleotides);
- Double helix made up of 2 strands held by hydrogen bonds;
- (Hydrogen bonds/pairing) between adenine, thymine andcytosine, guanine;
Which bases are purine and which are pyrimidine?
Adenine and Guanine: 2-ring purine bases
Thymine, Cytosine and Uracil: 1-ring pyrimidine bases
Name the complementary base pairs in DNA and their hydrogen bonds
Adenine + thymine : 2 H-bonds
Guanine + Cytosine: 3 hydrogen bonds
Name the complementary base pairs in RNA
2 H bonds between Adenine + Uracil
3 H bonds between guanine + cytosine
Relate the structure of DNA to its functions (6)
- sugar-phosphate backbone & many H-bonds provide stability
- long molecule stores lots of information
- helix is compact for storage in nucleus
- base sequence of triplets codes for amino acids
- double-stranded for semi-conservative replication
- complementary base pairings for accurate replication
- weak H-bonds break so strands separate for replication.
Describe the structure of messenger RNA (mRNA)
give 4 features
- single stranded & linear
- long ribose polynucleotide but shorter than DNA
- contains uracil instead of thymine base
- codon sequence is complementary to exons of 1 gene from 1 DNA strand
Relate the structure of messenger RNA to its function
- breaks down quickly so no excess polypeptide forms
- ribosome can move along strand & tRNA can bind to exposed bases
- can be translated into a specific polypeptide by ribosomes
Describe the structure of transfer RNA (trna)
- tRNA molecules have a characteristic cloverleaf shape
- are composed of a single strand of RNA with several loop structures.
Order DNA, mRNA and tRNA according to increasing length
tRNA
mRNA
DNA
Why did scientists initially doubt that DNA carried the genetic code?
- chemically simple molecules with few components
Why is DNA replication described as semi-conservative?
- strands from original DNA molecule act as a template
- new DNA molecule contains 1 parent strand and one new stand
Outline the process of semi-conservative DNA replication
- DNA helicase breaks H-bonds between base pairs
- Each strand acts as a template
- Free nucleotides form nuclear sap attach to exposed bases by complementary base pairing
- DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strands.
- DNA polymerase build the new strand in one direction (5’ to 3’ direction)
- DNA ligase joins Okizaki fragments on lagging strand by catalysing the formation of phosphodiester bonds.
- H-bonds reform
Describe the Meselson-Stahl experiment
- bacteria were grown in a medium containing heavy isotope N15 for many generation
- some bacteria were moved to a medium containing light isotope 14N. Samples were extracted after 1&2 cycle of DNA replication
- centrifugation formed a pellet. Heavier DNA( bases made from 15N) settled closer to bottom of tube.
- lighter DNA bases would settle towards the top of the tube
Explain how the Meselson-Stahl experiment validated semi-conservative replication.
- Because all the DNA molecules settled in the middle of the tube. meaning they contained both the heavy 15N and light 14N nitrogen and settled in the middle of the tube.
- As one strand of each DNA molecule would be from the original DNA containing the heavier nitrogen and the other (new) strand would be made using only the lighter nitrogen).
Why is water a polar molecule?
- unevenl distribution of electrons between H and O.
- forms A slightly negative oxygen and a slightly positive hydrogen
Explain five properties that make water important for organisms. (5)
- A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
- A solvent so (metabolic) reactions can occur
- High specific heat capacity so buffers changes in temperature;
- Large latent heat of vaporisation so provides a cooling effect (through evaporation);
- Cohesion (between water molecules) so supports columns of water (transpiration stream in plants
- Cohesion (between water molecules) so produces surface tension
supporting (small) organisms
What are inorganic ions and where are they found in the body?
- ions that do not contain carbon atoms
- they are found in the cytoplasm and extracellular fluid
- either in very high or low concentrations
State and explain the property of water that helps to prevent temperature
increase in a cell.
- High (specific) heat capacity;
- Buffers changes in temperature;
State and explain the property of water that can help to buffer changes in
temperature.
- water has a high specific heat capacity
- can gain energy without changing temperature or takes a lot of heat to change temperature
Give two properties of water that are important in the cytoplasm of cells.
For each property of water, explain its importance in the cytoplasm. (4)
- polar molecule
- acts as a universal solvent
- reactive
- takes place in hydrolysis/
condensation /named reaction
What are inorganic ions and where are they found in the body?
- ions that do not contain carbon atoms
- they are found in the cytoplasm and extracellular fluid
- either in very high or low concentrations
Explain the role of hydrogen ions in the body.
- high concentration of H+ ions = low acidic pH
- it determines the pH of bodily fluids including blood pH
- H+ ions interact with H-bonDs and ionic bonds in tertiary structure of proteins, which can cause them to denature
Explain the role of iron ions in the body.
- Fe2+ bInds to porphyrin ring to form haem group in haemoglobin
- are involved in the transfer of electrons during respiration and photosynthesis, so they are key to the biological generation of energy
- Haemoglobin is made up of four polypeptide chains that each contain one Fe2+
Explain the role of sodium ions in the body.
- involved in co-transport for absorption of glucose and amino acids in lumen of gut
- involved in transmission of neurons
Explain the role of phosphate ions in the body
- it is a component of DNA , ATP , NADP , cAMP
- involved in ATP synthesis
- responsible for the phosphorylation of molecules which lowers activation energy & speeds up metabolic processes
Describe the roles of iron ions, sodium ions, and phosphate ions in cells. (5)
Iron ions:
1. Haemoglobin binds/associates with oxygen
2. involved in the transfer of electrons during respiration and photosynthesis, so they are key to the biological generation of energy
Sodium ions:
2. Co-transport of glucose/amino acids (into cells);
3. (Because) sodium moved out by active transport/Na – K pump;
4. Creates a sodium concentration/diffusion gradient;
5. Affects osmosis/water potential;
Phosphate ions:
6. Affects osmosis/water potential;
Accept 5. OR 6. – not both
- Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
8. used to produce ATP;
9. Phosphorylates other compounds (usually) making them more reactive;
10. Hydrophilic/water soluble part of phospholipid bilayer/membrane;
A high concentration of sodium in the blood can affect blood volume and
cause hypertension.
Use your knowledge of water potential to suggest how high sodium
concentrations in the medicines taken could affect blood volume.
- (Sodium ions) lower the water potential (of blood);
- Water would move into the blood by osmosis (from cells/tissue fluid);
- Increasing the blood volume;
Explain the role of ATP in cells.
- energy released is coupled to metabolic reactions
- phosphate group phosphorylates compounds to make them more reactive
Give the equation for the hydrolysis of ATP. Include named enzyme.
ATP hydrolase catalyses ATP –> ADP + Pi
How is ATP resynthesized in cells?
- ATP synthase catalyses condensation reaction between ADP + Pi
- during photosynthesis & respiration
ATP is useful in many biological processes. Explain why. (4)
- Releases energy in small /
manageable amounts. - It is broken down in one step
- It’s an immediate energy
compound. - Phosphorylates substances and makes them more reactive/ lowers activation energy;
- It can be reformed/resynthesised.
