Biological Molecules Flashcards
What elements are common to all the molecules of life?
Carbon, Hydrogen and Oxygen
What are the four main groups of carbon based molecules common to all life forms?
Carbohydrates, Lipids, Proteins and Nucleic Acids
Which molecule forms part of the plasma membrane?
Phospholipids
Which biological molecule forms proteins?
Amino acids (and nucleic acids)
Which two biological molecules are the main respiratory substrates?
Lipids and Carbohydrates
What is a polymer?
A series of repeating units (monomers) joined together
What reaction joins two monomers together?
Condensation reaction
What reaction breaks down polymers?
Hydrolysis
What type of chemical bond is formed between monomers?
Covalent bond
Why is it known as a condensation reaction?
A molecule of water is produced/released
Describe the process of hydrolysis
A water molecule is used to break a covalent bond. An H and an OH group are joined to the monomers.
What type of reaction joins monosaccharides together?
Condensation reaction
What is a disaccharide and what is the bond involved?
Two monosaccharides joined together by a glycosidic bond
What type of reaction breaks down disaccharides?
Hydrolysis
What disaccharide is made by joining two glucose molecules?
Maltose
What disaccharide is made by joining fructose and glucose?
Sucrose
What disaccharide is made by joining glucose and galactose?
Lactose
What are the 3 types of polysaccharides that alpha-glucose can form?
-Amylose
-Amylopectin
-Glycogen
What type of reaction breaks polysaccharides apart?
Hydrolysis
Describe the structure of glycogen
Polymer of alpha-glucose it is highly branched
State the two structures that make up starch
Amylopectin and Amylose
Describe the structure and properties of starch
A mixture of two polysaccharides of alpha glucose. Amylose is a long branched chain of alpha glucose. The angles of the glycosidic bonds give it a coiled structure which makes it compact so it is good for storage. Amylopectin is a long branched chain of a glucose. Its side branches allow enzymes to get at the glycosidic bonds easily so glucose can be released quickly. It is insoluble in water
What’s the differences and similarities between starch and glycogen?
Glycogen is always branched, starch isn’t. Starch is found in plants, glycogen in animals. Both are energy stores, both made of alpha glucose.
How are the monosaccharides in cellulose arranged?
Alternative β-glucose molecules are turned upside down
Why are different enzymes needed to digest starch and cellulose?
Different shape molecule requires a different enzyme as they have different active site shapes. Cellulose is made of β-glucose and starch of α-glucose. 1,6 glycosidic bonds are only in starch. Starch is made of amylose and amylopectin, cellulose is linear and starch is branched
Based on the arrangement of cellulose molecules, explain why cell walls provide strength and support to plant cells.
-Cellulose molecules form hydrogen bonds with each other to make microfibrils
-Fibres are tough and flexible
1,6 glycosidic bonds are found on…
Amylopectin and Glycogen
β-glucose can be found only in…
Cellulose
Describe the structure of amylopectin, including the bonds involved and the shape
Amylopectin is a long branched chain of glucose. Its side branches, 1,4 and 1,6 glycosidic bonds, branched
What type of reaction joins nucleotides?
Condensation
What is semi conservative replication?
Half of the strands in each new DNA molecule are from the original DNA molecule
Why is it known as semi conservative replication?
Because the original strand is split in two and half of each strand comes from the original, half is conserved
What evidence do we have to prove there is two strands?
the Meselson and Stahl experiment
What enzyme breaks the hydrogen bonds between the bases?
DNA helicase
What enzyme adds new nucleotides to the new strand?
DNA polymerase
Why is one strand known as the template strand?
because it acts as a template for new nucleotides to create a new strand with the correct complimentary base pairing
State the enzymes involved in DNA replication
DNA helicase, DNA polymerase
Which enzyme separates the strands in DNA replication?
DNA helicase
State the role of DNA polymerase
joins nucleotides together in condensation reactions
State the steps of DNA replication in order
- DNA helicase separates the two strands by breaking the hydrogen bonds between bases
- Each strands acts as a template
- Free nucleotides attach to template strand through complementary base pairing
- DNA polymerase joins nucleotides by reforming hydrogen bonds between bases
- Replication is semi conservative as new DNA molecules contain one old strand and one new strand
The free nucleotides pair up with the exposed bases on the DNA strands based on which principle?
complementary base pairing
Name the 4 bases found in DNA, name the bond that form between them
Adenine - thymine (2 hydrogen bonds) Guanine - cytosine (3 hydrogen bonds)
Which molecules make up the backbone of a polynucleotide?
Phosphates and pentose/ribose sugars
Describe the difference between bacterial DNA and eukaryotic DNA
bacterial DNA is short, circular and not associated with proteins. Eukaryotic DNA is long, linear and associated with proteins to form chromosomes
What are the four differences between DNA and RNA?
thymine + uracil, deoxyribose + ribose, double stranded + single stranded, long strand + short strand
What is the structure of ATP?
it contains a ribose sugar, an adenine base but has three phosphate groups
What does the hydrolysis of ATP produce?
ADP + Pi
Give the equation for the formation of ATP
ADP + Pi = ATP (reversible reaction)
What are the differences between ATP and a DNA nucleotide?
ATP contains two more phosphate groups and is only made of adenine bases, DNA can have 4 different bases
State four roles of lipids
Source of energy, waterproofing, insulation, protection
What does a triglyceride consist of?
Glycerol and 3 fatty acids
What bonds hold a triglyceride together?
Ester bonds
How is a phospholipid different to a triglyceride and how is it similar?
Only 2 fatty acids, a phosphate head. Both have fatty acids
How many water molecules are needed when breaking down a triglyceride?
3
What is the term for the reaction that forms lipids?
Condensation reaction
Describe how phospholipids can form a bilayer arrangement
- Hydrophilic heads point outwards
- Hydrophobic tails point inwards
State the monomer of a protein
amino acids
What are the components that make up an amino acid?
central carbon - H atom - amine group - carboxyl group
What part of the amino acid is variable and how many types are there?
R group - 20
Name the bond formed between two amino acids
peptide bond
What is the primary structure of a protein?
amino acid sequence
What is the secondary structure of a protein?
alpha helix + beta pleated sheets
What is the tertiary structure of a protein?
folding into a 3D shape
What is the quaternary structure of a protein?
binding with other subunits
State the bonds in a secondary protein
Hydrogen bonds
State the bonds in the tertiary structure of proteins
Ionic, hydrogen, disulphide bridges
Name the reaction that breaks down proteins
hydrolysis
Why does increasing the temperature of a reaction increase the rate of reaction?
as temperature increases so does the rate of reaction because there is more kinetic energy so the molecules move faster increasing the number of collisions and therefore the number of ES-complexes formed
If you were to increase the concentration of substrate in a reaction but the rate of reaction did not increase, what would you suggest is the limiting factor?
enzyme concentration
How can the pH affect the rate of an enzyme controlled reaction?
Above and below the optimum pH for each enzyme the H+ ions and OH- ions disrupt the ionic and hydrogen bonds holding the enzymes tertiary structure in place.
At extremes of pH the active site changes shape and no more ES-complexes can be formed as the substrate no longer fits. The enzyme is permanently denatured, the reaction stops.
Describe the test for a reducing sugar and state the positive result
add benedict’s reagent, heat
positive result= turns from blue to orange/brown
What can be done if the test for a reducing sugar produces an negative result but sugars should be present?
Take another sample, add HCl and heat in water bath, then add NaOH to neutralise. Add benedict’s then heat
Why is the benedict’s test known as a semi-quantitative test
because it tells you how much sugar there is but not exactly how much (not fully quantitative
How can we use a colorimeter to do a quantitative benedict’s test?
-Colorimeters measure the absorbance or transmission of light by a coloured solution
-More concentrated solution, more light absorbed/less light transmitted
-Compare to data table (known concentrations vs abs/trans value)
Describe the test for starch and state the positive result
add iodine solution, if starch is present it will change from orange/brown to blue/black
Describe the test for protein and state the positive result
add biuret solution, if proteins are present then the solution will turn from blue to purple
Describe the test for lipids and state the positive result
mix the sample with ethanol, mix solution with water then shake,
white emulsion layer forms if a lipid is present
