2.2 Biological molecules Flashcards
What is a covalent bond?
when 2 atoms share a pair of electrons
What is an ion?
an atom/molecule in which the total number of electrons is not equal to the total number of protons
What is an ion that has a net positive charge and has lost electrons called?
a cation
What is an ion that has a net negative charge and has gained electrons?
an anion
What is Ca2+ necessary for?
nerve impulse transmission and muscle contraction
What is HCO3- necessary for?
maintenance of blood pH
Define polarity
When the electrons shared in a covalent bond are not shared equally between the 2 atoms in the bond
Is the atom in a covalent bond with the greater share of electrons delta positive or delta negative?
delta negative
What bonds form between polar molecules?
Hydrogen bonds
Name 3 characteristics of water
- unusually high boiling point
- ice is less dense than water
- has cohesive and adhesive properties
Name 4 properties of water that make it critical in sustaining life
- water acts as a solvent
- water is an effective transport medium due to cohesive/adhesive properties
- water acts as a coolant
- water is stable
What is the general formula of carbohydrates?
Cx(H2O)y
Name 3 types of carbohydrate
- monosaccharide
- disaccharide
- polysaccharide
Name 3 examples of monosaccharides
- glucose (hexose)
- fructose (hexose)
- ribose (pentose)
Name 2 examples of disaccharides
- lactose
- sucrose
Name 3 examples of polysaccharides
- glycogen
- cellulose
- starch
What is the chemical formula of glucose?
C6H12O6
What is a condensation reaction?
when 2 OH groups react and a covalent bond is formed and a water molecule is formed
How is starch formed?
When many alpha-glucose molecules join by glycosidic bonds to form 2 different polysaccharides (amylose and amylopectin) collectively known as starch
What is the difference between amylose and amylopectin?
amylose is formed of alpha-glucose molecules joined only by 1,4-glycosidic bonds and is a straight chain whereas amylopectin also has 1,6-glycosidic bonds and is branched
What is glycogen?
The functionally equivalent energy storage molecules to starch in animals and fungi
How does glycogen differ from amylopectin?
Glycogen forms more branches so is more compact - important as animals are mobile
Key properties of amylopectin and glycogen that make them suitable for storage
- insoluble
- branched
- compact
What is a hydrolysis reaction?
the addition of H2O to break covalent bonds
How is cellulose formed?
beta-glucose molecules join with each alternate molecule being turned upside down, forming a straight chain
How are microfibrils formed?
Cellulose molecules make H-bonds with each other forming microfibrils
How are macrofibrils formed?
microfibrils join together to form macrofibrils
How are cellulose fibres formed?
Macrofibrils joining together
What properties make cellulose good for forming cell walls?
cellulose fibres are insoluble and strong
What is the test for reducing sugars?
Benedict’s test
What colour indicates a positive result in Benedict’s test for reducing sugars?
brick red, depending on the concentration - negative result is blue
What is the iodine test used for?
to detect the presence of starch
How can carbohydrate concentration be quantitatively determined?
using a colorimeter
What are lipids more commonly known as?
fats or oils
Are lipids polar or non-polar?
non-polar
How is a triglyceride made?
combining 1 glycerol molecule with 3 fatty acids
What is a fatty acid?
Carboxylic acids with a hydrocarbon chain attached
What is the name of the reaction that forms triglycerides?
esterification which is a type of condensation reaction
What does saturated mean?
all the carbon atoms in the hydrocarbon chain form the maximum number of bonds with hydrogen atoms
What are phospholipids?
modified triglycerides with a phosphate group replacing one of the fatty acid groups
How is a phospholipid bilayer formed?
the hydrophilic head of the phospholipids will be attracted to the water and the hydrophobic tails will point towards the centre of the sheet
What are sterols?
steroid alcohols based on a 4-C ring structure with an OH group at one end
Name one example of a sterol
cholesterol
What is the function of cholesterol?
plays an important role in the formation of cell membranes
Name 5 biological roles of lipids
- membrane formation
- hormone production
- electrical insulation
- waterproofing
- buoyancy
How are lipids identified?
emulsion test
What are peptides?
polymers made up of amino acid molecules
What do proteins consist of?
one or more polypeptides arranged as complex macromolecules
How many essential amino acids are there that can only be obtained from diet?
9
How are peptides synthesised?
condensation reaction of amino acids to form peptide bonds
What catalyses the reaction that forms polypeptides?
Peptidyl transferase
What technique is used to separate different amino acids?
Thin layer chromatography
What are the 4 levels of protein structure?
primary, secondary, tertiary and quaternary
What is the primary structure of a protein?
the sequence of amino acids
What is the secondary structure of a protein?
The interaction of the O, H and N atoms in the basic repeating structure of the amino acids (not R groups) forming alpha helices and beta pleated sheets
What is the tertiary structure of a protein?
the folding of the protein into its final shape involving a number of different interactions
What are the interactions involved in the tertiary structure of a protein?
- Hydrophobic and hydrophilic interactions
- Hydrogen bonds
- Ionic bonds
- Disulphide bonds/bridges
What reaction is responsible for the breakdown of proteins?
Hydrolysis
How are proteins identified?
Biuret test - purple result is positive, blue result is negative
What are the 2 different types of proteins?
globular and fibrous
What are 3 properties of globular proteins?
- Compact
- Water soluble
- Roughly spherical in shape
What is an example of a globular protein?
Insulin
What is a conjugated protein?
A type of globular protein that contains a prosthetic group
What is a prosthetic group?
a non protein component
What are the 2 types of prosthetic groups?
- Lipids/carbohydrates forming lipoproteins/glycoproteins
- Metal ions/molecules derived from vitamins forming cofactors
What is are 2 examples of conjugated proteins?
Haemoglobin and catalase
What does catalase do?
catalyses the breakdown of hydrogen peroxide
What are 3 properties of fibrous proteins?
- long
- insoluble
- strong and stable
What are 3 examples of fibrous proteins?
- Keratin
- Collagen
- Elastin
Where is keratin found in the body?
hair, skin and nails
What makes keratin so strong?
presence of many disulphide bonds
Where is elastin found in the body?
walls of blood vessels and alveoli
What is elastin made up of?
lots of molecules of tropoelastin
Why can elastin stretch?
The tropoelastin molecules contain alternate hydrophobic and lysine-rich areas and get are able to stretch and recoil without breaking
What is collagen?
a connective tissue found in skin, tendons, ligaments and the nervous system
Describe the structure of collagen
3 polypeptides wound together in a long, strong rope-like structure in a triple helix. It is flexible. It is strong due to tropocollagen fibrils cross-linking to produce strong fibres.
What are nucleic acids?
large polymers formed from nucleotides
two types - DNA and RNA
What are the 3 components of a nucleotide?
- a pentose sugar
- a phosphate group
- a nitrogenous base
What is the name of the bond between the phosphate group of one pentose sugar and the hydroxyl group on another pentose sugar?
Phosphodiester bond
What are the 4 possible bases on a DNA nucleotide?
- Cytosine
- Guanine
- Adenine
- Thymine
What are the 2 groups that the DNA bases can be classed as?
- Pyrimidines
- Purines
What is complementary base pairing?
A and T can form 2 H-bonds and always join with each other and C and G can form 3 H-bonds so also join with each other
What is RNA?
Ribonucleic acid
What essential role does RNA play?
- transfer of genetic information from DNA to the proteins that make up the enzymes and tissues of the body
How does RNA differ from DNA?
- ribose sugar
- uracil instead of thymine
Why is RNA required?
DNA is too large to leave the nucleus so a gene is transcribed to a mRNA molecule which is small enough to leave the nucleus
What is semi-conservative replication?
Double helix unwinds and separates into 2 strands and free DNA nucleotides then pair with their complementary bases via H-bonds. The new nucleotides join to their adjacent nucleotides with phosphodiester bonds. Each new molecule of DNA consists of 1 new strand and 1 old strand.
What are the 2 enzymes involved in replication?
- DNA helicase unwinds DNA double helix
- DNA polymerase catalyses the formation of phosphodiester bonds
What is continuous replication?
The strand that is unzipped from the 3’ end can be continuously replicated as the strands unzip.
What is discontinuous replication?
The other strand that is unzipped from the 5’ end so DNA polymerase has to wait until a section of the strand has unzipped and then work back along the strand producing Okazaki fragments
What is the genetic code?
DNA carries ‘instructions’ needed to synthesise the many different proteins required by organisms. These proteins are made up of a sequence of amino acids, folded into complex structure, therefore DNA must code for a sequence of amino acids
What is a codon?
a sequence of 3 bases that code for an amino acid
How many different base codons are possible?
64
How many stop codons are there and how many amino acids do they code for?
- 3 stop codons that do not code for any amino acids and signal the end of the sequence
What does degenerate code mean?
There are only 2o different amino acids that regularly occur in biological proteins and there are a lot more codons, therefore many amino acids can be coded for by more than one codon which makes the code degenerate.
What is transcription?
The copying of the base sequences of genes and transporting them to the ribosome.
What is translation?
The decoding of the mRNA into a sequence of amino acids
What are the 3 main types of activity that cells require energy for?
- Synthesis
- Transport
- Movement
What is ATP made up of?
- a nitrogenous base - always adenine
- a pentose sugar - always ribose
- 3 phosphate groups
How much energy is released by ATP?
30.6 kJ/mol
How does ATP release energy?
hydrolysis to form ADP and Pi
What are the properties of ATP that make it ideally suited to carry out its function in energy transfer?
- small
- water soluble
- contains bonds between phosphates with intermediate energy
- releases energy in small packets
- easily regenerated by phosphorylation of ADP
