1.1- Molecules Flashcards
What elements are present in the largest proportion of living organisms
Carbon, hydrogen, nitrogen, phosphorus, sulfur
What type of bonding is present in water
Covalent bonds
Describe the term polar
Molecules with an uneven distribution of charge
What does the polar nature of water cause?
Hydrogen bonds are formed between adjacent water molecules, between the oxygen in water molecule and the hydrogen on another.
What kinds of molecules dissolve in water?
Molecules with charged groups and ions
What is waters value as a solvent?
Most of a cells reactions take place in an aqueous solution
It acts as a transport medium in living organisms
It has different effects on hydrophilic and hydrophobic molecules
What does the term ‘hydrophilic’ mean
It describes molecules which are ‘water loving’ ( dissolve in water )
How does pH affect protein shape and function?
When a protein is not in its optimal pH it will work much slower
What is a Buffer?
A chemical or substance that resist changes to pH and ensure that an environment maintains a particular pH
When would a buffer be used?
In practical investigations involving enzymes. They help to regulate the pH
Importance of calcium ions.
Mammals- essential component of bones and teeth, essential in blood clotting
Plants- essential component of the middle lamella of plant cell walls
Importance of Iron (Fe2+) ions.
Part of the haem group in haemoglobin
Importance of magnesium ions.
Gives chlorophyll its light-absorbing properties
Importance of potassium ions
Maintains electrical gradients across neurones
Importance of Nitrate ions.
Component in amino acids, nucleic acids and chlorophyll
Importance of phosphate ions
Important component in cell membranes, also a major component in other molecules such as nucleic acids
Importance of hydrogencarbonate ions
Acts as a natural buffer
What elements do carbohydrates contain?
Carbon,hydrogen,oxygen
What are the three main groups of carbohydrates?
Monosaccharides
Disaccharides
Polysaccharides
What are monosaccharides?
Basic carbohydrate monomers (sugars)
What are disaccharides?
Double sugars formed from two monosaccharides monomers
What are Polysaccharides?
Complex molecules usually consisting of many monosaccharide monomers
What are the three monosaccharides to remember.
alpha-glucose
Beta-glucose
Fructose
How does beta glucose differ from alpha glucose?
The hydroxyl group is reversed in beta glucose
Molecular formula of glucose/fructose
C6H1206
What is an isomer?
Substances with the same molecular formula but different structural formula
How are disaccharides formed?
When two monomers ( usually hexoses ) react together via condensation
How can a condensation reaction be reversed?
A hydrolysis reaction
What is the difference in a condensation reaction and hydrolysis reaction
Condensation- loses a water molecule
Hydrolysis- gains a water molecule
What is the bond that forms between two hexose sugars?
A glycosidic bond
What is the bond between the two alpha glucose in maltose called?
A 1-4 glycosidic bond
General formula for disaccharides
C12H22O11
What is sucrose made up of?
An alpha glucose and fructose monomer
Function of maltose
Formed when starch is digested, further digestion forms glucose
Function of sucrose
Form in which carbohydrates are transported through phloem in plants
What are polysaccharides and how are they formed?
Complex carbohydrates often forming very long chains.
Formed through condensation reactions joining a large number of monomers together, forming a polymer
What is the general formula of a polysaccharide?
(C6H10O5)n
What is the monomers of starch?
Alpha glucose
What two types of chains is starch made up of?
Amylose
Amylopectin
Describe the structure of Amylose
Alpha- 1-4 glycosidic bonds, forms an unbranched chain in a coiled configuration
How does the structure of amylopectin differ from amylose?
On top of the alpha - 1-4 glycosidic bonds it contains alpha 1-6 glycosidic bonds producing a branched molecule
How often do branches occur in amylopectin?
Every 1-10 alpha-glucose monomers
Why is starch such a good storage molecule?
Their structures are very compact ( aided by coiled configuration )
Insoluble therefore will not affect water relations in the cell
As its large it can be retained in the cell
The branching nature of amylopectin creates many terminal ends that can be easily hydrolysed ( this aids rapid breakdown into glucose during times of high respiratory demand)
Where is starch located?
Chloroplasts in plants
How does the structure of Glycogen differ from amylopectin?
They both have 1-4 and 1-6 glycosidic bonds but the chains are more branched in glycogen and shorter than amylopectin chains
Where is glycogen stored?
Liver and muscle cells
How is glycogen a better storage molecule than starch
As it has no unbranched chains and shorter chains it has proportionally more terminal ends enabling faster hydrolysis
What is the role of cellulose?
Structural
What monomers is cellulose made up of?
Beta glucose
What bonds are present in cellulose ?
Beta - 1-4 glycosidic bonds
Hydrogen bonds between each chain in microfibrils
Why must every other monomer be inverted in cellulose?
Beta glucose has a different structure than alpha glucose therefore needs to be flipped
What two effects come from flipping adjacent beta glucose monomers?
Unbranched chains are straighter ( bulky CH2OH side groups alternate between above and below the chain )
Hydrogen bonds are able to form cross linkages between adjacent chains ( as there is oxygen and the side groups available on both sides )
What elements do lipids contain?
Carbon, Hydrogen and oxygen
What are the main types of lipids?
Triglycerides, phospholipids, waxes and steroids
State the structure of a triglyceride
A glycerol and three fatty acids
What reaction occurs to join the glycerol with the three fatty acids?
Three condensation reactions
What bond is formed between the glycerol and fatty acids after condensation?
An ester bond.
Define the term unsaturated
have at least one C=C double bond in the chain
What is the difference in monounsaturated and polyunsaturated
Mono describes when there’s only 1 C=C double bond
Poly is more than one
How are triglycerides an excellent energy store? What else are they used for?
They release more energy per unit mass than carbohydrates
Insulation
Many body organs use fat as a protective layer
How do phospholipids differ from triglycerides?
A fatty acid molecule is replaces by a phosphate group
What part of a phospholipid is hydrophilic?
The phosphate group ( head )
What elements does proteins contain?
Carbon hydrogen oxygen and nitrogen ( usually contains sulfur )
How do amino acids differ from each other?
They have different ‘R’ groups
What bonds link together amino acids?
Peptide bonds
Where does the condensation reaction occur in proteins?
Between the amino group of one acid and the carboxyl group of another
What is the primary structure in proteins
The sequence of amino acids
What is the secondary structure of proteins?
The twisting of the primary structure due to the formation of hydrogen bonds to create an alpha helix
OR
The formation of pleated sheets due to the formation of hydrogen bonds to create beta pleated sheets.
How do proteins differ from each other?
The order of their amino acids
What is the Tertiary structure?
The further folding of the secondary structure giving it a unique 3D shape
What bonds are involved in the tertiary structure?
Hydrogen bonds
Ionic bonds - formed between the amino and carboxyl groups in some R groups
Disulfide bonds- covalent bonds formed between R-groups of sulfur containing amino acids.
What is the importance of disulphide bonds?
Very strong and provide strength to structural (fibrous) proteins such as collagen
How does hydrophobic interactions affect the tertiary structure?
Amino acids with hydrophobic R groups tend to take up positions of the molecule surrounded by other parts of the polypeptide
What is the Quaternary structure?
Proteins which consist of two or more polypeptides bonded together
What are conjugated proteins?
A quaternary structure that has a prosthetic group
Describe the structure of haemoglobin
Four polypeptides ( two each from two different polypeptides ) each attached to an iron-rich haem group.
What is a fibrous protein?
One which consists of chains that form fibres/sheets. Parallel chains are linked by cross bridges
What is a fibrous protein?
One which consists of chains that form fibres/sheets. Parable chains are linked by cross bridges
What is the role of a fibrous protein?
Structural
Describe the structure of collagen
Three identical alpha-helix polypeptides intertwined, held together by hydrogen bonds.
Where is collagen found, what is its role?
Tendons that link muscle to bone, it’s very strong and doesn’t stretch when tension is applied
What role do globular proteins have?
Metabolic
List some examples of globular proteins
Enzymes, antibodies, haemoglobin
What are prions?
A type of protein found in mammals and some other animal groups.
Where are prions found?
In the nervous system
Short hand for the normal form of a prion
PrP or PrP^c
Short hand for a disease-causing prion
PrP^Sc
What happens when one disease-causing prion is present in an individual
It can act as a template for other prions to convert to the disease causing prion
What can be caused when too many disease-causing prions are present?
Neurodegenerative disorders in the brain, eventually causing death
What are two key features of disease causing prions
The can replicate
They are infectious
How can diseases associated with PrP^Sc arise?
Normal proteins can Spontaneously adopt the PrP^Sc form
Mutations in the DNA that codes for the prion protein. This can cause the disease-causing prion to be passed from parent to offspring.
Through eating prion-rich contaminated food
What type of diseases can prions cause.
Scrapie- affects sheep
bovine spongiform encephalopathy- BSE or ‘ mad cow disease ‘
Variant Creutzfeldt-Jakob disease- vCJD, this is a human version of BSE normally through eating contaminated beef
What are the sub-units of nucleic acids, what are their components?
A nucleotide.
A pentode sugar
A phosphate group
A nitrogenous base
What reaction bonds the components in nucleic acids? What bonds link the pentose sugars to the phosphates?
Condensation reaction.
Phosphodiester bonds
What is a nucleic acid?
A chain of nucleotides ( polynucleotide ) with a free 5’ end ( phosphate ) and a free 3’ end (sugar)
What are the two types of nucleic acids?
Deoxyribonucleic acid ( DNA ) and ribonucleic acid ( RNA )
Describe the structure of DNA
two anti-parallel strands held together by hydrogen bonds between adjacent bases
anti-parallel - the two strands are running in opposite directions
Organised in a double helix with there being 10 base pairs for each complete turn of the helix
What are the base pairings in DNA?
Adenine - Thymine
Guanine- Cytosine
How does the structure of RNA differ from DNA?
It has a ribose sugar rather than a deoxyribose ( both are Pentose )
It is single stranded rather than double stranded
It’s much shorter than DNA
Uracil replaces thymine , A U C G
What are the three types of RNA?
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
What is the function of DNA?
They regulate development of living organisms through protein synthesis. I.e the regulation of enzymes. The sequence of bases in DNA determines the amino acid sequence of polypeptides.
One of the strands is the ‘template’ functioning as the genetic code, each base triplet e.g AGT codes for ONE amino acid.
What is a gene?
A sequence of DNA that codes for a polypeptide
Describe the role of messenger RNA
Carries the code from the DNA in the nucleus to a ribosome in the cytoplasm
Describe the role and structure of Transfer RNA, How many types of tRNA are there?
Carries the amino acids to the mRNA where protein synthesis takes place.
They have a similar structure except for the part that links with the appropriate amino acid.
There are as many different types as there are amino acids.
Describe the function of Ribosomal RNA
Made in the nucleolus and it forms over half the mass of each ribosome
When does DNA replication take place?
BEFORE chromosome duplication in the process of mitosis and meiosis
What enzyme ‘unzips’ ( breaks the hydrogen bonds ) in DNA replication?
DNA helicase
What enzyme joins the new nucleotides of each strand in DNA replication?
DNA polymerase
What does DNA polymerase do?
Reforms the phosphodiester bonds between the phosphate and deoxyribose sugar
Outline the process of DNA replication
DNA helicase breaks the hydrogen bonds between the bases in DNA
Each of the original strands become templates where free nucleotides are linked following base pairing rules
These nucleotides are joined together by DNA polymerase which forms phosphodiester bonds between the phosphate and deoxyribose sugar.
Why is DNA replication described as ‘ semi-conservative replication ‘
Each of the new molecules contains one original and one new strand
What experiment proved the semi-conservative model ?
The Meselson and Stahl experiment ( 1958 )
Outline the Meselson and Stahl experiment.
They cultured the bacterium - Escherichia coil - using the heavy nitrogen (15) isotope
The bacteria were transferred to a medium containing light nitrogen (14)
Describe the results obtained from the Meselson and Stahl experiment
After one generation- the intermediate band is explained as all DNA have one light and one heavy strands I.e medium weight
After two generations- Half the DNA was light and half was medium as the light strands gained another light strand and the heavy strands gained another light strand
