Topic 3 - The chemistry of life Flashcards
What are the most occurring chemical elements in living things?
Carbon, hydrogen, oxygen, and nitrogen
What other elements are needed by living organisms? (besides C, H, O, N)
Sulfur, calcium, phosphorus, iron, sodium
What is the role of sulfur?
Needed to make amino acids
What is the role of calcium?
Acts as a messenger, binds to proteins that regulate processes inside cells.
What is the role of phosphorus?
A part of the phosphate groups in ATP and DNA molecules
What is the role of iron?
Needed to make cytochromes (proteins used for electron transport)
(also haemoglobin)
What is the role of sodium?
- Creating action potential in neurons
- Pumped into the cytoplasm to raise the solute concentration and cause osmosis
Draw a diagram showing the structure of water molecules to show their polarity and hydrogen bond formation
What are the thermal properties of water?
- High specific heat capacity → water can absorb or give off lots of heat without great temperature change in itself (e.g. stable body temperature
What are the cohesive properties of water?
- Causes droplets, surface tension, ability to move as a column in xylem, and high heat capacity and vaporisation (bonds need to be broken)
What is cohesion?
Attraction of kind molecules due to polar covalent bonding
What are the solvent properties of water?
- Dissolves polar molecules, including carbohydrates, proteins, nucleic acids
- Also the medium in which biochemistry of the cell occurs (cytoplasm, nucleoplasm, stroma, blood plasma)
Is water a good transport medium?
Yes. (e.g. blood)
Distinguish between organic and inorganic compounds
Compounds containing carbon that are found in living orgamisms (except hydrogencarbonates and oxides of carbon) are regarded as organic.
What is the general chemical structure of amino acids?
The R group varies
What is the chemical structure of ribose?
What is the chemical structure of glucose?
What is the general chemical structure of fatty acids?
The number of n group varies
List three examples of monosaccharides, disaccharides, and polysaccharides
Monosaccharides: glucose, galactose, fructose
Disaccharides: maltose, lactose, sucrose
Polysaccharides: starch, glycogen, cellulose
What is one function of glucoes in animals?
Chemical fuel for cell respiration
What is one function of lactose in animals?
The sugar in milk that provides energy for young animals
What is one function of glycogen in animals?
Stores glucose for short-term energy store in liver and muscles
What is one function of fructose in plants?
Makes fruits sweet, attracting animals
What is one function of sucrose in plants?
Carried by the phloem to transport energy to cells throughout the plant
What is one function of cellulose in plants?
Used to make strong fibres that construct the cell wall
What is a condensation reaction?
Joining two molecules to form a larger molecule. Water is also formed.
What are condensation reactions used for?
- Creating polypeptides from amino acids
- Creating di and polysaccharide from monosaccharides
- Creating lipids (glyceride) from fatty acids
Outline the condensation of amino acids
amino acid + amino acid → protein (dipeptide) + water
What is hydrolysis?
Breaking down large molecules into smaller molecules with the help of water. Hydrolysis is the reverse of condensation
Outline examples of hydrolysis reactions with polypeptides, polysaccharides, and glycerides
Polypeptides + water → dipeptides or amino acids
Polysaccharides + water → disaccharides or monosaccharides
Glycerides + water → fatty acids + glycerol
What are three functions of lipids?
- Energy storage in the form of fats (animals) and oils (plants)
- Heat insulation (a layer of fat under the skin)
- Buoyancy (less dense than water so help animals to float)
What are the advantages of lipids over carbohydrates in energy storage?
- Contain more energy per gram → stores of lipid are lighter than store of carbohydrate of the same amount of energy
- Insoluble in water → do not cause problems with osmosis in cells
What are the advantages of carbohydrates over lipids in energy storage?
- More easily digested than lipids → energy can be released more rapidly
- Soluble in water → easier to transport
What are the components of a DNA nucleotide? Draw a simple diagram
- A sugar (deoxyribose)
- A phosphate group
- A nitrogenous base (A,C,T,G)
What are the names of the four bases in DNA?
- Adenine
- Thymine
- Guanine
- Cytosine
How are DNA nucleotides linked together into a single strand?
By covalent bonds between the sugars and phosphate groups
How are complementary base pairings formed between bases?
- Hydrogen bonds between the bases
- Adenine and thymine are able to form only two hydrogen bonds so they’re linked
- Cytosine and guanine are able to form three hydrogen bonds so they’re linked
Draw a simple structure of the molecular structure of DNA, showing both strands and complementary base pairing
What are the three stages of DNA replication?
- Unwinding and separation
- Complementary base pairing
- Rewinding
What happens in the unwinding and separation of DNA in DNA replication?
- An enzyme called helicase unwinds and separates the two strands by breaking the hydrogen bonds between the bases
What happens in the complementary base pairing in DNA replication?
- Free nucleotides in the replication fork form hydrogen bonds with the bases on the parent strand
- DNA polymerase is the enzyme that does this
What happens in the rewinding of DNA in DNA replication?
- The new copied DNA rewinds and detaches from the parent DNA
How is complementary base pairing relevant in conserving the base sequence of DNA?
Both parent strands are bonded to their complementary bases in replication so that two identical molecules are formed.
What is meant by semi-conservative DNA replication?
Each molecule formed consists of one new strand and one old strand.
What are the differences between DNA and RNA?
DNA VS RNA
- Two strands VS one strand
- Deoxyribose VS ribose
- A, C, G, and T VS A, C, G, and U
Outline the stages of DNA transcription
- DNA unwinds and two strands separate
- Free RNA nucleotides assemble according to the DNA strand
- The nucleotides are linked and a strand of RNA (mRNA) forms
- The mRNA separates from the DNA
- The DNA goes back to its double helix
1, 2, and 3 are carried out by RNA polymerase
What is the form of genetic code?
A triplet code. Three bases code for one amino acid
What is a codon?
A group of three bases
Outline the stages of translation
- mRNA binds to the small subunit of the ribosome
- Each tRNA molecule has a special triplet of bases called an anticodon and carries the amino acids corresponding to this anticodon
- tRNA molecules bind to the ribosome, two at once. Each codon on the mRNA finds its anticodon on some tRNA. The bases on the codon and anticodon form hydrogen bonds
- The amino acids on the tRNAs are bonded together by a peptide link forming a polypeptide
- One tRNA detaches and the ribosome moves along to the next codon and another tRNA carrying another amino acid binds to it.
- Rinse and repeat until a polypeptide is formed
What is meant by the one gene-one polypeptide hypothesis?
There is almost always a single gene to code for a polypeptide, which does not code for any other polypeptide
What are exceptions to the one gene-one polypeptide hypothesis?
- Some genes code for tRNA or mRNA, not polypeptides
- Some DNA sequences act as regulators of gene expression and are not translated (introns)
- In lymphocyts, pieces of DNA from different parts are spliced together and transcribed and translated to produce antibodies. Different lymphocytes produce different antibodies by splicing their DNA in different ways.
What is an enzyme?
Globular proteins which act as catalysts of chemical reactions
What is an active site?
A region on the surface of an enzyme to which substrates bind and which catalyses a chemical reaction involving the substrates.
What is meant by enzyme-substrate specifity?
Enzymes are highly specific and catalyse very few different reactions → a very small number of possible substrates.
Specificy is due to the delicate shape of the active site, like a lock and a key.
What is denaturation?
A change in the structure of an enzyme so that it can no longer carry out its function.
What is the effect of temperature on enzyme activity?
- Activity increases exponentially as temperature increases (rate doubles with every 10°C rise)
- At high temperatures enzymes become denatured and stop working → rate drops rapidly
- Denaturation is due vibrations inside the enzyme caused by temperature → bonds inside the enzyme are broken
What is the effect of pH on enzyme activity?
- Every enzyme has its optimum pH (usually 7)
- At this pH the enzyme activity is fastest
- As pH increases or decreases from the optimum, activity is rapidly reduced
- Wrong pH alters the shape of the active site
What is the effect of substrate concentration on enzyme activity?
- At low concentrations, activity increases steeply → random collisions between substrate and active site happen more frequently
- At high concentrations the activity reaches a plateau because most of the active sites are occupied
How is lactase used in the production of lactose-free milk?
- Lactose is converted into glucose and galactose by lactase
- Lactase can be added to milk
- Lactase can also be immobilised on a surface of a porous material, milk is then allowed to flow past it → avoids contamination of the product with lactase
What are the reasons for using lactase in food processing?
- Some people are lactose intolerant
- Galactose and glucose are sweeter than lactose so less sugar needs to be added
- Glucose and galactose are more soluble than lactose, giving a smoother texture in ice cream
- Bacteria ferment glucose and galactose so the production of yoghurt etc. is faster
What is cell respiration?
The controlled release of energy, in the form of ATP, from organic compounds in cells.
What happens to glucose in cell respiration?
Glucose in the cytoplasm is broken down by glycolysis into pyruvates, with a small yield of ATP
What happens in anaerobic cell respiration?
In humans, the pyruvate is converted to lactate (lactic acid)
In yeast, the pyruvate is converted to ethanol and carbon dioxide
What happens in aerobic cell respiration?
The pyruvate is broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP
What is photosynthesis?
The conversion of light energy into chemical energy
What is sunlight composed of?
A wide range of wavelengths (colours)
What are pigments?
Substances that can absorb light
What is the main photosynthetic pigment?
Chlorophyll
What are the differences in absorption of red, blue, and green light by chlorophyll?
Red and blue are absorbed more than green. The green light that cannot be absorbed is reflected (gives the green colour of plants)
What is light energy used for in plants?
To produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen
What is carbon fixation?
The conversion of carbon in gas to carbon in solid compounds with the help of hydrogen and ATP
What factors can be used to measure the rate of photosynthesis?
- Production of oxygen
- Volume of O2 produced can be measured - Uptake of carbon dioxide
- If CO2 is absorbed from water, the pH rises - Increase in biomass
What is the effect of temperature on the rate of photosynthesis?
- As temperature increases the rate increases exponentially
- Reaches an optimum temperature
- Above the optimum temperature the rate falls steeply
What is the effect of light intensity on the rate of photosynthesis?
- The rate is directly proportional to light intensity
- At high intensity the rate reaches a plateau
What is the effect of CO2 concentration on the rate of photosynthesis?
- No photosynthesis at very low concentrations
- At low to fairly high concentration the rate is proportional to the concentration
- At very high concentration the rate reaches a plateau
