biological molecules Flashcards
1
Q
What is a molecule?
A
The complex formed when two or
more atoms bond together
2
Q
What are covalent bonds?
A
Bond that occur when two atoms share a pair of electrons. The electrons used to form bonds are unpaired and present in the outer orbitals of the atoms
3
Q
What are covalent bonds?
A
Bond that occur when two atoms share a pair of electrons. The electrons used to form bonds are unpaired and present in the outer orbitals of the atoms
4
Q
What are the bonding rules for
carbon, nitrogen, oxygen and
hydrogen atoms?
A
- Carbon atoms form 4 bonds
- Nitrogen atoms form 3 bonds
- Oxygen atoms form 2 bonds
- Hydrogen atoms form 1 bonds
5
Q
What is an ion?
A
An atom or molecule with an overall
electric charge because the total
number of electrons is not equal to
the total number of protons
6
Q
What is an ionic bond?
A
A chemical bond that involves the donating of an electron from one atom to another, forming positive and negative ions held together by the attraction of the opposite charges
7
Q
What is a cation?
A
An atom or molecule that loses one
or more electrons giving it a net
positive charge
8
Q
What is an anion?
A
An atom or molecule that gains one
or more electrons giving it a net
negative charge
9
Q
What are ions in solution
called?
A
Electrolytes
10
Q
List all of the important cations
in living organisms
A
- Calcium ions (Ca2+)
- Sodium ions (Na+)
- Potassium ions (K+)
- Hydrogen ions (H+)
- Ammonium ions (NH4+
11
Q
List all of the important anions
in living organisms
A
- Nitrate ions (NO3-)
- Hydrogen carbonate ions (HCO3-)
- Chloride ions (Cl-)
- Phosphate ions (PO43-)
- Hydroxide ions (OH-)
12
Q
What are the following cations necessary for? 1. Calcium ions 2. Sodium ions 3. Potassium ions 4. Hydrogen ions 5. Ammonium ions
A
1. Nerve impulse transmission and muscle contractions 2. Nerve impulse transmission and kidney function 3. Nerve impulse transmission and stomatal opening 4. Catalysis of reactions and pH determination 5. Production of nitrate ions by bacteria
13
Q
What are the following anions necessary for? 1. Nitrate ions 2. Hydrogen carbonate ions 3. Chloride ions 4. Phosphate ions 5. Hydroxide ions
A
1. Nitrogen supply to plants for amino acid and protein formation 2. Maintenance of blood pH 3. Balance positive charge of sodium and potassium ions in cells 4. Cell membrane formation, nucleic acid and ATP formation, bone formation 5. Catalysis of reactions and pH determination
14
Q
List the 4 biological molecules
and the element present in
each of them
A
• Carbohydrates - carbon, hydrogen, and oxygen usually in the ration Cx(H2O)x • Lipids - carbon, hydrogen, and oxygen • Proteins - carbon, hydrogen, oxygen, nitrogen, and sulphur • Nucleic acids - carbon, hydrogen, oxygen, nitrogen, and phosphorus
15
Q
What are the monomers in
carbohydrates and proteins
called?
A
In carbohydrates the monomers
are sugars (saccharides) monosaccharides
• In proteins the monomers are
amino acids
16
Q
What are the monomers in
carbohydrates and proteins
called?
A
In carbohydrates the monomers
are sugars (saccharides)
• In proteins the monomers are
amino acids
17
Q
Why are some molecules
polar?
A
• In covalent bonds the electrons are not always shared equally by the atoms of different elements • The atoms with the greater share of negative electrons will be slightly negative compared with the other atom in the bond, which will be slightly positive • Polar molecules have regions of negativity and regions of positivity
18
Q
Why is water a polar
molecule?
A
• Oxygen always has a much greater share of electrons in an OH bond • Many organic molecules contain hydroxyl (OH) groups, and so are slightly polar; water is an example
19
Q
What are hydrogen bonds, and
what causes them?
A
Hydrogen bonds are relatively weak interactions • They are caused by polar molecules interacting with each other and forming bonds - hydrogen bonds
20
Q
List the properties of water
A
- Liquid
- Density
- Solvent
- Cohesion and surface tension
- High specific heat capacity
- High latent heat of vaporization
21
Q
Why is water a liquid at room
temperature?
A
• The hydrogen bonds between
water molecules make it more
difficult for them to escape to
become a gas
22
Q
What is the importance of
water being a liquid at room
temperature, to living
organisms?
A
• Provides habitats for living things in rivers, lakes and seas • Forms a major component of the tissues in living organisms • Provides a reaction medium for chemical reactions • Provides an effective transport medium e.g. in blood and vascular tissue
23
Q
Describe how the density of
water changes, as H2O
changes state
A
Usually the solid is more dense than the liquid form of a substance. However ice is less dense than water because as water goes from 4C to freezing point, the water molecules form a structure that is less dense than liquid water
24
Q
What is the importance of
water’s density to living
organisms?
A
If water was less dense, aquatic organisms would find it very difficult to float Ice floats on water so: • Aquatic organisms have a stable environment to live through in winter • Ponds are insulated against extreme cold because the ice layer reduces heat loss from the pond
25
Why is water a good solvent?
```
• As it is polar, the positive and
negative parts of the water
molecules are attracted to the
oppositely charged parts of the
solute
• Water molecules cluster around
the charged parts of the solute
molecules or ions, which helps to
separate them and keep them
apar
```
26
What is the importance of
water being a good solvent to
living organisms?
```
• Molecules and ions can move
around and react together in water
e.g. as in the cytoplasm of cells,
which is >70% water
• molecules and ions can be
transported around living things
whilst dissolved in water
```
27
Describe cohesion and surface
| tension of water
```
• Water molecules demonstrate
cohesion because hydrogen
bonding between the molecules
pulls them together
• Water molecules demonstrate
surface tension because they are
more attracted to the water
molecules beneath them than air
molecules above, so the water
contacts, giving the surface of the
water the ability to resist a force
applied to it
```
28
What is the importance of
cohesion and surface tension
of water to living organisms?
```
Columns of water in plant vascular
tissue are pulled up the xylem
tissue together from the roots due
to cohesion
• Insects like pond-skaters can walk
on water due to surface tension
```
29
Why does water have a high
| specific heat capacity?
```
• Water molecules are held together
quite tightly by hydrogen bonds
• Therefore you need to put in a lot
of heat energy to increase their
kinetic energy and temperature
• This means that water doesn’t
heat up or cool down easily
```
30
What is the importance of the
high specific heat capacity of
water to living organisms?
```
• Living things need a stable
temperature for enzyme-controlled
reactions to happen properly
• Aquatic organisms need a stable
environment in which to live
```
31
Why does water have a high
| latent heat of vaporisation?
```
Because the water molecules are
held together by hydrogen bonds, a
relatively large amount of energy is
needed for water molecules to
evaporate
```
32
what is the importance of the
high latent heat of
vaporisation of water to living
organisms?
```
Water can help to cool living things
and keep their temperature stable
e.g.
• Mammals are cooled when sweat
evaporates
• Plants are cooled when water
evaporates from mesophyll cells
```
33
What is the importance of
water’s role as a reactant to
living organisms
```
It is a reactant in reactions such as
photosynthesis, and in hydrolysis
reactions such as digestion of
starch, proteins and lipids
• Plays a very important role in the
digestion and synthesis of large
biological molecules
```
34
What are carbohydrates?
```
Organic polymers composed of the
elements carbon, hydrogen and
oxygen, usually in the ration
Cx(H2O)y. Also known as
saccharides or sugars
```
35
# Define the following:
1. Monosaccharide
2. Disaccharide
3. Polysaccharide
```
1. A single sugar molecule e.g.
glucose, fructose and ribose
2. A molecule comprising two
monosaccharides joined
together by a glycosidic bond
3. A polymer made up of many
monosaccharides e.g. glycogen,
cellulose and starch
```
36
Describe glucose
```
• C6H12O6
• Hexose monosaccharide (because
it has 6 carbons)
• Polar and soluble in water due to
the hydrogen bonds that form
between the OH group and water
molecules
• Means glucose is dissolved in the
cytosol of the cell
2 variations
• Alpha glucose - OH group is
below carbon 1
• Beta glucose - OH group is above
carbon 1
```
37
How do alpha glucose
molecules react with each
other?
```
• The OH groups on C1 and C4
reacted forming a 1,4 glycosidic
bond (covalent)
• Condensation reaction because a
water molecule is formed (lost)
```
38
```
What do the following
combinations form?
1. a-glucose + a-glucose
2. a-glucose + fructose
3. B-galactose + a-glucose
4. B-glucose+ B-glucose
```
1. Maltose
2. Sucrose
3. Lactose
4. Cellobiose
39
What are pentose
monosaccharides? Give
examples
```
• Sugars that contain 5 carbon
atoms
• e.g. ribose which is the sugar
present in RNA nucleotides
• e.g. deoxyribose which is the
sugar present in DNA nucleotides
```
40
What is starch?
A polysaccharide formed from alpha
glucose molecules either joined to
form amylose or amylopectin. Found
in plants
41
Describe amylose
```
• Found in plants
• Alpha glucose
• Glycosidic bonds between C1
andC4
• Coils into a spiral shape held
together by hydrogen bonds
• OH groups on C2 inside of the
coil, making the molecule less
soluble and allowing hydrogen
bonds to form to maintain the
coil’s structure
```
42
Describe amylopectin
```
• Found in plants
• Alpha glucose
• Has glycosidic bonds between C1
and C4, and also has branches
formed by glycosidic bonds
between C1 and C6
• Coils into a spiral shape held
together by hydrogen bonds, but
with branches coming out of the
spiral
```
43
What is glycogen?
A branched polysaccharide formed
from alpha glucose. A chemical
energy store in animal cells
44
Describe glycogen
```
• Found in animals
• Like amylopectin with glycosidic
bonds between C1 and C4, and
branches formed by glycosidic
bonds between C1 and C6
• The C1 C4 bonded chains are
smaller than in amylopectin so
glycogen has less tendency to coil
• Has more branches than
amylopectin making it more
compact
• Easier to remove monomer units
as there are more ends
```
45
How do beta-glucose
molecules react with each
other?
```
• The OH groups on C1 and C4 are
to far away to react, so each
alternate beta glucose molecule
must be turned upside down to
reach
• It is unable to could or form
branches
• A straight chain molecule called
cellulose is formed
```
46
Describe cellulose
```
• Cellulose molecules make
hydrogen bonds with each other
forming microfibrils
• Microfibrils join together to form
macrofibrils that combine to
produce fibres
• The fibres are strong and insoluble
and are used to make cell walls
```
47
Why is cellulose a good
| material for cell walls?
```
Microfibrils and macrofibrils have
very high tensile strength because
of the glycosidic bonds and
hydrogen bonds
• macrofibrils run in all directions,
criss-crossing the wall for extra
strength
• Space between macrofibrils for
water and mineral ions to pass in
and out of the cell, making the cell
wall full permeable
```
48
What are lipids?
```
Non-polar macromolecules contains
the elements carbon, hydrogen and
oxygen. Soluble in alcohol rather
than water. Include triglycerides,
phospholipids and sterols
```
49
Formation of a triglyceride
50
What are triglycerides?
```
Lipids composed of one glycerol
(C3H8O3) molecule and three fatty
acids. Fatty acids are carboxylic
acids that consist of a carboxyl
group (-COOH) which a hydrocarbon
chain attached.
```
51
How are triglycerides formed?
```
• The hydroxyl groups in the fatty
acid molecule and glycerol
molecule react
• This leads to the formation of 3
water molecules and bonds
between the fatty acid and
glycerol molecule
• The bonds are called ester bonds,
and the reaction is called
esterification
• Esterification is an example of a
condensation reaction
```
52
What is the difference between
saturated and unsaturated
triglycerides?
```
• Fatty acid chains that have no
double bonds between the carbon
atoms are saturated, and vice
versa
• If there’s 1 double bond =
monounsaturated
• If there’s 2 or more double bonds
= polyunsaturated
```
53
How does the presence of
double bonds in unsaturated
triglycerides cause?
```
• Changes the bond angle and
causes the molecule to kink or
bend
• Therefore the molecules cannot
pack so closely together
• Makes them liquid at rtp rather
than solid, so they are oils rather
than fats
```
54
What type of triglycerides do
| plants contain?
Unsaturated triglycerides, which
| normally occur as oils
55
Which type of triglycerides are
| healthier?
Unsaturated triglycerides are
healthier for human than
triglycerides or (solid) fats
56
What are phospholipids?
Modified triglycerides, where one
fatty acid has been replaced with a
phosphate group. They are found in
the cytoplasm of very cell
57
Phospholipid
58
What are the characteristics of
| phospholipids?
```
• Have a non-polar end (the fatty
acid chains) which are
hydrophobic and repelled by water
• Have a charged head (the
phosphate PO43-) which are
hydrophilic and attracted to water
```
59
How do phospholipids interact
| with water?
When phospholipids are mixed with water, they form a phospholipid bilayer or double layer due to their amphipathic nature. The polar hydrophilic head group will interact with water to form hydrogen bonds with water but the two hydrophobic tails made of non-polar hydrocarbon tails repel water
60
How do the characteristics of
phospholipids help in the
formation of cell membranes?
```
• The bilayer arrangement means
that they can separate the aqueous
environment in which cells usually
exist, from the aqueous cytosol
within the cells
```
61
What are sterols?
Steroid alcohols. Complex alcohol
molecules based on a 4 carbon ring
structure with a hydroxyl (OH) group
at one end
62
Describe the characteristics of
| sterols
```
Have a dual hydrophilic/hydrophobic
characteristics. The hydroxyl group
is polar and therefore hydrophilic,
and the rest of the molecule is
hydrophobic.
```
63
What is cholesterol?
```
• A type of sterol
• The body primarily manufactures it
in the liver and intestines
• Vitamin D, steroid hormones and
bile are all manufactured using
cholestero
```
64
What is the importance of
cholesterol in the formation of
cell membranes?
```
Positioned between the
phospholipids with the hydroxyl
group at the periphery of the
membrane
• Adds to the stability of cell
membranes
```
65
What is the importance of
cholesterol in regulating the
fluidity of cell membranes?
Keeps membranes fluid at low
temperatures and stops them
becoming too fluid at high
temperatures
66
What are the roles of lipids?
| Due to their non-polar nature
```
• Membrane formation and the
creation of hydrophobic barriers
• Hormone production
• Electrical insulation necessary for
impulse transmission
• Waterproofing, e.g. in birds’
feathers and on plant leaves
```
67
What are the roles of
| triglycerides in particular
```
• Long-term energy storage
Stored under the skin and around
vital organs where they provide:
• Thermal insulation to reduce heat
loss, e.g. in penguins
• Cushioning to protect vital organs
e.g. heart and kidneys
• Buoyancy for aquatic animals like
whales
```
68
# Define the following:
1. Proteins
2. Peptides
3. Peptide bond
4. Amino acid
```
1. One or more polypeptides
arranged as a complex
macromolecule
2. Chains of two or more amino
acid molecules
3. Bond formed between two
amino acids
4. Monomer used to build
polypeptides and thus proteins
```
69
Amino acid
70
Describe what happens when
| two amino acids react together
```
• The hydroxyl in the carboxylic acid
group of one amino acid reacts
with a hydrogen in the amine
group of another amino acid
• A peptide bond is formed between
the amino acids and water is
produced (condensation reaction)
• The resulting compound is a
dipeptide
```
71
When is a polypeptide formed?
```
• When many amino acids are joined
together by peptide bonds
• This reaction sis catalysed by the
enzyme peptide transferase
present in ribosomes, the sites of
protein synthesis
```
72
What happens to the R-groups
of the amino acids when the
amino acids react?
```
• Different R-groups interact with
each other (R-group interactions)
forming different types of bond
• These bonds lead to polypeptides
folding into complex structures
(proteins)
```
73
What does the presence of
different sequences of amino
acids lead to?
```
Different structures with different
shapes being produced
The very specific shapes of proteins
are vital for the many functions
proteins have within living organisms
```
74
What is the primary structure
| of proteins?
```
• The sequence in which the amino
acids are joined
• Directed by information carried
within DNA
• The amino acids in the sequence
will influence how the
polypeptide’s fold to give the
proteins final shape, and
determine its function
• The only bonds here are peptide
bonds
```
75
What is the secondary
| structure of proteins?
```
• The oxygen, hydrogen, and
nitrogen atoms of the amino acids
(excluding R groups) interact
• A result of hydrogen bonds and
forms at regions along long protein
molecules depending on the
amino sequences
```
76
What are the two types of
| secondary structure?
```
• Alpha Helix - Hydrogen bonds
form within the amino acid chain,
pulling it into a coil shape called
an alpha-helix
• Beta Pleated Sheet - Polypeptide
bonds lie parallel to each other
joined by hydrogen bonds, forming
sheet-like structures.The pattern
formed by individual amino acids
makes the structure appear
pleated
```
77
What is tertiary structure?
```
• The folding of a protein into its
final shape
• Often includes sections of
secondary structure
• The coiling or folding of sections
of proteins into their secondary
structures brings R-groups of
different amino acids closer
together so they can interact
```
78
List the interactions that occur
| between R-group
```
Hydrophobic and
hydrophilicinteractioncs - weak
interactions between polar and
non-polar R-groups
• Hydrogen bonds - these are the
weakest of bonds formed
• Ionic bonds - stronger than
hydrogen bonds and form
between oppositely charged Rgroups
• Disulfide bonds/bridges - covalent
and the strongest of the bonds but
only form between R-groups that
contain sulphur atoms
```
79
What is quaternary structure?
```
• Protein structure where a protein
consists of more than 1
polypeptide chain, e.g insulin has
a quaternary structure
• Results from the association of 2
or more individual proteins called
subunits
• The interaction between subunits
are the same as in tertiary
structure except between different
protein molecules rather than
within one molecule
• The protein subunits can be
identical or different
```
80
Describe hydrophilic and
hydrophobic interactions in
proteins
```
• Proteins are assembled in the
aqueous environment of the
cytoplasm
• The way a protein will fold also
depends on whether the R-groups
are hydrophilic or hydrophobic
• Hydrophilic groups arena the
outside, whilst hydrophobic are on
the inside of the molecule (away
from the cytoplasm
```
81
List the types of proteins
* Globular proteins
* Conjugated proteins
* Fibrous proteins
82
What are globular proteins?
```
Compact, spherical, water-soluble
proteins
• Form when proteins fold into their
tertiary structures so that the
hydrophobic R-groups on the
amino acid are kept away from the
aqueous environment
• Hydrophilic R-groups on the
outside of the protein meaning the
proteins are soluble in water
• e.g. Insulin
```
83
Describe how the structure of
| Insulin is suited to its function
```
• Globular protein
• Hormone involved in regulation of
blood glucose concentration
• Hormones are transported in the
bloodstream so need to soluble
• Hormones have to fit into specific
receptor on cell-surface
membranes to work, therefore
need to have precise shapes
```
84
What are conjugated proteins?
```
Globular proteins that contain a
prosthetic group.
Lipids or carbohydrates can
combine with proteins forming
lipoproteins or glycoproteins. Metal
ions and molecules derived from
vitamins also form prosthetic groups
• e.g. Haemoglobin and Catalase
both contain prosthetic harm groups
(Fe2+)
```
85
Describe how the structure of
haemoglobin makes it suited
to its function
```
Red, oxygen-carrying pigment in
red blood cells
• Quaternary protein made from 4
polypeptides (2 alpha and 2 beta
subunits)
• Each subunit contains a prosthetic
hem group
• The Fe2+ ions in the haem groups
are each able to combine
reversibly with an oxygen molecule
which enables haemoglobin to
transport oxygen around the body
```
86
Describe how the structure of
catalase makes it suited to its
function
```
• An enzyme
• A quaternary protein containing 4
prosthetic harm groups
• The presence of Fe2+ ions in the
haem groups allow catalase to
interact with hydrogen peroxide
and speed up its breakdown
• Hydrogen peroxide is a common
byproduct of metabolism but
damaging to cells and cell
components, so catalase makes
sure it doesn’t accumulate
```
87
What are fibrous proteins?
```
Long insoluble, structural proteins
• Due to the presence of a high
proportion of amino acids with
hydrophobic R-groups in their
primary structures
• Amino acid sequence in primary
structure is usually very repetitive
leading to very organised
structures
• Are NOT folded into complex 3D
shapes like globular proteins
• E.g. Keratin, Elastin and Collagen
```
88
Describe how the structure of
| keratin is suited to its function
```
• Group of fibrous proteins
presenting hair, skin and nails
• Large proportion of the sulfurcontaining amino acid cysteine
leading to many strong disulphide
bonds forming strong, inflexible,
insoluble materials
• Hair contains fewer disulphide
bonds than nails, so is more
flexible
```
89
Describe how the structure of
| elastin is suited to its function
```
• Fibrous protein found in elastic
fibres
• Elastic fibres are present in the
walls of blood vessels and in the
alveoli of the lungs
• Give these structures flexibility to
expand when needed but also to
return to their normal size
• Quaternary protein made from
many stretch molecules called
tropoelastin
```
90
Describe how the structure of
collagen makes it suited to its
function
```
• Fibrous protein
• Connective tissue found in skin,
tendons, ligaments and the
nervous systems
• Many different forms but all are
made up of 3 polypeptides wound
together in a long and strong ropelike structure
• Like rope, collagen has flexibility
```
91
Describe the test for starch
```
1. Add iodine solution (in
potassium iodide) to a sample
2. If starch is present, you will see a
colour change from yellowbrown to blueback
• When dissolved in potassium
iodide, the iodine (I2) forms a
triiodide I3-, which slips into the
middle of the amylose helix,
causing a colour change
```
92
Describe the test for reducing
sugars (all monosaccharides
and some disaccharides)
1. Place the sample in a boiling
tube. If its not liquid, grind it up
or lend it in water
2. Add an equal volume fo
Benedict’s solution
3. Heat the mixture gently in a
boiling water bath for 5 minutes
Blue > Green > Yellow > Orange >
Red
• Benedict’s reagent is an alkaline
solution of copper (II) sulphate
• The more reducing sugar present,
the more brick-red precipitate
formed and the less blue Cu2+
ions left in solution
93
Describe the test for nonreducing sugars
```
1. Do Benedict’s test for reducing
sugars, the result will be
negative
2. Sucrose is the most common
non-reducing sugar
3. If sucrose is first boiled with
dilute hydrochloric acid then it’ll
give a positive result when
warmed with Benedict’s solution
• This is because the sucrose has
been hydrolysed by the acid to
glucose and fructose, both
reducing sugars
```
94
Describe the test for lipids
1. Mix the sample with ethanol
2. The resulting solution is mixed
with water and shaken
3. If a white emulsion forms as a
layer on top the solution, this
indicated the presence of a lipid
4. If the solution remains clear, the
test is negative
95
Describe the test for proteins
```
1. Add Biuret A (sodium hydroxide)
and then Biuret B (copper
sulphate) to the sample
2. If a protein is present, the colour
changes from light blue to lilac/
mauve
```
96
What are nucleic acids?
Large polymers formed from
nucleotides. Contain the elements
carbon, nitrogen, hydrogen,
phosphorus, and oxygen
97
Describe the composition of
| nucleotides
```
• A pentose monosaccharide
containing 5 carbon atoms
• A phosphate group, (PO42-) and
inorganic molecule that is acidic
and negatively charged
• A nitrogenous base - a complex
organic molecule containing 1 or 2
carbon rings in its structure, as
well as nitrogen
```
98
How do nucleotides link
together to form a
polynucleotide?
```
By condensation reactions
• Phosphate group at the 5th carbon
of the pentose sugar (5’) of one
nucleotide forms a covalent bond
with the hydroxyl (OH) group at the
3rd carbon (3’) of the pentose
sugar of another nucleotide
• These bonds are called
phosphodiester bonds
• Forms a long, strong sugarphosphate ‘backbone’
• Phosphodiester bonds are broken
by hydrolysis
```
99
What is Deoxyribonucleic acid
| (DNA) ?
```
The molecule responsible for the
storage of genetic information
• The sugar is deoxyribose, which
has 1 less oxygen atoms than a
ribose sugar
• The nucleotides each have 1 of 4
different bases: Adenide, Thymine,
Guanine, or Cytosine
```
100
What are pyrimidines?
• Single-ringed, nitrogenous bases
that form part of a nucleotide
• Smaller bases
• Thymine (T) and Cytosine (C
101
What are purines?
• Double-ringed, nitrogenous bases
that form part of a nucleotide
• Larger bases
• Adenine (A) and Guanine (G
102
Describe the double helix
| structure of DNA
```
Made up of 2 strands of
polynucleotides coiled into a helix
• The 2 strands are held together by
hydrogen bonds between the
bases
• Each strand has a phosphate
group (5’) at one end, and a
hydroxyl group (3’)at the other end
• The 2 parallel strands run in
opposite directions - antiparallel
```
103
What is complementary base
| pairing?
```
Specific hydrogen bonding between
nucleic acid bases. A binds to T or
U, C binds to G
• A and T form 2 hydrogen bonds so
always join with each other
• C and G form 3 hydrogen bonds
so always join with each other
```
104
What are the consequences of
| complimentary base pairing?
```
• A small pyrimidine base always
binds to a larger purine base; this
arrangement keeps a constant
distance between the DNA
backbones, resulting in parallel
polynucleotide chains
• DNA always has equal amounts of
adenine and thymine, and cytosine
and guanine
```
105
What is Ribonucleic acid?
| (RNA
```
Polynucleotide molecules involved in
the copying and transfer of genetic
information from DNA.
The monomers are nucleotides
consisting of a ribose sugar and 1 of
four bases: Adenine, Uracil,
Cytosine, or Guanine
```
106
What are the similarities and
differences between DNA and
RNA?
```
Similarities:
• RNA nucleotides form polymers in
the same way as DNA nucleotides
- by the formation of
phosphodiester bonds
Differences:
• In RNA the pentose sugar is
ribose, meanwhile in DNA it’s
deoxyribose
• In RNA, the thymine base is
replaced with Uracil
```
107
What is DNA replication?
The semi-conservative process of
the production of identical copies of
DNA molecules
108
What is semi-conservative
| replication?
DNA replication results in one old
strand and one new strand present
in each daughter DNA molecules
109
Describe the process of semiconservative replicatio
```
1. The enzyme DNA helicase
travels along the DNA backbone,
catalysing reactions that breaks
the hydrogen bonds between
complimentary base pairs
2. After the ‘unzipping’, free DNA
nucleotides will then pair with
their complimentary bases,
which have been exposed as the
strands separate
3. Hydrogen bonds are formed
between the new complimentary
bases
4. The enzyme DNA polymerase
catalyses the formation of
phosphodiester bonds between
adjacent new nucleotides
```
110
What is a mutation?
```
A change in the genetic material
which may affect the phenotype of
the organism.
Happen due to random error in the
replication of DNA that lead to a
change in the sequence of bases
```
111
What is the genetic code?
The sequences of baes in DNA are
the ‘instructions’ for the sequences
of amino acids in the production of
proteins
112
What is a triplet code?
```
The genetic code is a sequence of
three nucleic acids bases, called a
codon. Each codon codes for one
amino acids.
A section of DNA that contains the
complete sequence of baes
(codons) to ode for an entire protein
is called a gene
```
113
What is a triplet code?
```
The genetic code is a sequence of
three nucleic acids bases, called a
codon. Each codon codes for one
amino acids.
A section of DNA that contains the
complete sequence of baes
(codons) to ode for an entire protein
is called a gene
```
114
Why is the genetic code a
| degenerate code?
```
• There are 64 different base triplets
or codons possible, but there are
only 20 amino acids
• Therefore, many amino acids can
be coded for by more than one
codon
```
115
How are genes read?
```
• There’s a start codon (ATG) that
signals the start of a sequence
that codes for a protein (if it’s in
the middle of a gene it codes for
methionine)
• Having a start codon means that
codons are read ‘in frame’, so the
genetic code is non-overlapping
• There are 3 stop codons that don’t
code for any amino acids, and
signal the end of the sequence
```
116
What is transcription?
```
The process of copying smaller
sections of DNA base sequence to
produce smaller molecules of
mRNA, which can be transported
out of the nucleus via the nuclear
pores, to the site of protein
synthesis
```
117
Describe the process of
| transcription
```
1. A gene unwinds and unzips,
aided by DNA helicase, and the
hydrogen bonds between
complimentary nucleotide bases
break
2. The sense strand (5’ to 3’) codes
for the protein, whilst the
antisense strand (3’ to 5’)acts as
the template strand during
transcription
3. RNA polymerase catalyses the
formation of temporary hydrogen
bonds between RNA nucleotides
and their complimentary DNA
bases on the template strand
4. The strand of RNA produced is
complimentary to the template
strand, so is a copy of the
sense/ coding strand
5. Messenger RNA (mRNA) passes
out of the nucleus, through the
nuclear envelope, whilst the DNA
double helix reforms
```
118
What are ribosomes made up
| of? (eukaryotic cells)
2 subunits, one large and one
small
• Almost equal amounts of protein
and ribosomal RNA (rRNA)
119
What is the role of rRNA?
• Maintaining the structural stability
of the protein synthesis sequence
• Biochemical role in catalysing the
reaction
120
What happens to mRNA after it
| has left the nucleus?
```
• Binds to a specific site on the
small subunit of a ribosome
• The ribosome holds mRNA in
position while it is translated into a
sequence of amino acids
• This process is called translation
```
121
What is translation?
```
The process by which the
complementary code carried by
mRNA is decoded by tRNA into
sequence of amino acids. This
occurs at a ribosome
```
122
What is transfer RNA (tRNA)?
```
Form of RNA that carries an amino
acid specific to its anticodon to the
correct position along mRNA during
translation
• Single stranded polynucleotides,
but can twist into a hairpin shape
• At one end is a trio of nucleotide
bases that recognises and
attaches to a specific amino acid
• At the loop is another triplet of
bases called an anticodon that is
complementary to a specific
codon of bases on the mRNA
```
123
Describe how translation
| happens at a ribosome
```
1. mRNA binds to the small subunit
of the ribosome at its start
codon (AUG)
2. A tRNA with the complementary
anticodon (UAC) binds to the
mRNA start codon. This tRNA
carries the amino acid
methionine
3. Another tRNA with the
complementary anticodon, and
carrying an amino acid, binds to
the next codon on the mRNA. A
maximum of 2 tRNAs can be
bound at the same time
4. The 1st amino acid (methionine)
is transferred to the amino acid
on the 2nd tRNA by the
formation of a peptide bond.
This is catalysed by the enzyme
peptidyl transferase, which is an
rRNA component of the
ribosome
5. The ribosome then moves along
the mRNA, releasing the 1st
tRNA. The 2nd tRNA becomes
the 1st
6. Stages 3-5 are repeated until the
ribosome reaches the end of the
mRNA at a stop codon, and the
polypeptide is released
```
124
What is ATP?
```
Adenosine triphosphate
A nucleotide composed of a
nitrogenous adenine base, a
pentose sugar, and 3 phosphate
groups. The ‘universal energy
currency’ for cells, because it is
used for energy transfer in all cells.
```
125
What are the 3 main types of
activity cells require energy
for?
```
• Synthesis - e.g. of large molecules
such as proteins
• Transport - e.g. pumping
molecules or ions across cell
membranes by active transport
• Movement - e.g. protein fibres in
muscle cells that cause muscle
contraction
```
126
What is ADP?
```
Adenosine diphosphate
A nucleotide composed of a
nitrogenous adenine base, a
pentose sugar and 2 phosphate
groups
Formed by the hydrolysis of ATP,
releasing a phosphate ion and
energy
```
127
Why is ATP not a good longterm energy sto
```
• The instability of the phosphate
bonds
• Fats and carbohydrates are better
long-term energy stores
• Energy released in the breakdown
of these molecules (a process
called cellular respiration) is used
to create ATP
• A phosphate group is reattached
to an ADP molecule
(phosphorylation which is an
example of a condensation
reaction)
```
128
Why do cells not store large
| amounts of ATP?
```
• Due to the instability of ATP
• Instead ATP is rapidly reformed by
the phosphorylation of ADP
• Interconversion of ATP and ADP is
happening constantly in all living
cells, so cells don’t need a large
store of ATP
• ATPis a good immediate energy
store
```
129
How does ATP carry energy?
```
1. When a cell needs energy, ATP is
broken down to ADP and Pi
2. In the hydrolysis reaction, a
phosphate bond is broken and
energy released to be catalysed
by the enzyme ATP hydrolase
3. ATP hydrolysis can be couple to
other reactions in the cell - the
energy can be used directly to
make the coupled reaction
happen (instead of being lost as
heat)
4. The released phosphate can be
added to another compound
(phosphorylation) which often
makes the compound more
reactive
5. ATP can be re-synthesised in a
condensation reaction between
ADP and Pi. The enzyme ATP
synthase catalyses it during both
respiration and photosynthesis
```
130
What are the properties of ATP
that make it suited to carry out
its function in energy transfer?
```
• Small - moves easily into, out of,
and within cells
• Water soluble - energy requiring
processes happen in aqueous
environments
• Contains bonds between
phosphates with immediate
energy: large enough to be useful
for cellular reactions, but not so
large that energy is wasted as heat
• Releases energy in small quantities
- quantities are suitable to most
cellular needs, so that energy is
not wasted as heat
• Easily regenerated - can be
recharged with energy
```
