3 - Biological molecules Flashcards
1
Q
What are the six most abundant elements in living organisms?
A
Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), and Sulfur (S).
2
Q
What role does hydrogen (H+) play in biological molecules?
A
- Catalysis of reactions
- pH determination
3
Q
What is the role of calcium (Ca+) in biological systems?
A
- nerve impulse transmission
- muscle contraction
4
Q
What is the role of sodium ions in biological systems?
A
- nerve impulse transmission
- kidney function
5
Q
What is the role of ammonium (NH4-) ions in biological systems?
A
production of nitrate ions by bacteria
6
Q
What is an anion?
A
a positive ion
7
Q
What is a cation?
A
a negative ion
8
Q
What is the role of nitrate ions (NO3-) in biological systems?
A
- nitrogen supply to plants for amino acid and protein formation
9
Q
What is the role of hydrogen carbonate ions (HCO3-)in biological systems?
A
maintenance of blood pH
10
Q
What is the role of Chloride ions (Cl-) in biological systems?
A
balance the positive charge of sodium ions and potassium ions in cells
11
Q
What is the role of phosphate ion (PO4 3-)s in biological systems?
A
- cell membrane formation
- nucleic acid and ATP formation
- bone formation
12
Q
What is the role of hydroxide ions (OH-) in biological systems?
A
- catalysis of reactions
- pH determination
13
Q
What elements are in carbohydrates?
A
carbon, hydrogen and oxygen
14
Q
What elements are in lipids?
A
carbon, hydrogen, oxygen, nitrogen and sulphur
15
Q
What elements are in nucleic acids?
A
carbon, hydrogen, oxygen, nitrogen and phosphorus
16
Q
Explain the structure of a water molecule?
A
-Water is composed of atoms of hydrogen and oxygen. One atom of oxygen combines with two atoms of hydrogen by sharing electrons (covalent bonding)
-Although water as a whole is electrically neutral the sharing of the electrons is uneven between the oxygen and hydrogen atoms
-The oxygen atom attracts the electrons more strongly than the hydrogen atoms, resulting in a weak negatively charged region on the oxygen atom (δ-) and a weak positively charged region on the hydrogen atoms(δ+), this also results in the asymmetrical shape
-This separation of charge due to the electrons in the covalent bonds being unevenly shared is called a dipole. When a molecule has one end that is negatively charged and one end that is positively charged it is also a polar molecule
-Water is a polar molecule
17
Q
What is a hydrogen bond?
A
-Hydrogen bonds form between water molecules
-As a result of the polarity of water hydrogen bonds form between the positive and negatively charged regions of adjacent water molecules
-Hydrogen bonds are weak, when there are few, so they are constantly breaking and reforming. However when there are large numbers present they form a strong structure
18
Q
What do hydrogen bonds contribute to?
A
-An excellent solvent – many substances can dissolve in water
-A relatively high specific heat capacity
-A relatively high latent heat of vaporisation
-Water is less dense when a solid
-Water has high surface tension and cohesion
-It acts as a reagent
19
Q
How does water act as a solvent?
A
- when water is mixed with other polar molecules, it will orient itself so that its slightly negatively charge area is facing and attracted to the positively charged solute molecules.
- this strong attracting is enough to break the solutes bond and separate it into its components
20
Q
How is water being a solvent important for life?
A
-Chemical Reactions: Water serves as the medium for chemical reactions in biological systems, facilitating processes like digestion, photosynthesis, and cellular respiration.
-Transport of Nutrients: Water dissolves essential nutrients and minerals, allowing them to be transported within living organisms, providing nourishment to cells.
-Metabolic Reactions: Water is involved in metabolic reactions, serving as a solvent for reactants and products, aiding in the regulation of metabolic processes.
-Ecological Importance: In ecosystems, water serves as a universal solvent, playing a crucial role in nutrient cycling and supporting aquatic life.
-Waste Removal: Water dissolves metabolic waste products, allowing for their elimination from the body, maintaining proper functioning.
21
Q
water and its High specific heat capacity.
A
- SHC is the amount of thermal energy needed to raise the temperature of 1kg by 1’C
- waters is 4200j/kg’c which is high. it is due to many hydrogen bonds in water where lots of energy is needed to overcome them, thus the temperature of water does not fluctuate greatly
22
Q
How is water having a high specific heat capacity important for life?
A
-Temperature Regulation: Water’s high specific heat capacity allows it to absorb and store a large amount of heat energy without a significant temperature increase. This property helps stabilize temperature in living organisms.
-Environmental Stability: Bodies of water, such as oceans and lakes, have relatively stable temperatures due to water’s high specific heat. This stability provides a more hospitable environment for aquatic life
-Cellular Function: Water’s temperature stability is essential for maintaining consistent conditions within cells. This stability is crucial for the proper functioning of enzymes and other cellular processes.
23
Q
What is latent heat of vaporisation in water?
A
In order to change state (from liquid to gas) a large amount of thermal energy must be absorbed by water to break the hydrogen bonds and evaporate
24
Q
How is water having a latent heat of vaporization important for life?
A
Temperature Regulation: When water evaporates, it absorbs a significant amount of heat energy from its surroundings. This cooling effect is essential for regulating temperature in living organisms.
Heat Dissipation/Thermoregulation: The ability to release heat through evaporation, such as through sweating in humans or transpiration in plants, helps prevent overheating and maintain optimal internal temperatures.
Water Cycle: The latent heat of vaporization plays a key role in the water cycle, as it powers the evaporation of surface water, cloud formation, and precipitation, ensuring the availability of fresh water for all living organisms.
25
What is cohesion in the context of water?
-Cohesion refers to the tendency of water molecules to be attracted to and stick to each other due to hydrogen bonding.
-Water is a polar molecule with a partial positive charge on hydrogen and a partial negative charge on oxygen, allowing water molecules to form hydrogen bonds and stick together.
26
What is the significance of cohesion in water's role in plant biology?
-This allows columns of water to move through the xylem of plants and through blood vessels in animals
-This also enables surface tension where a body of water meets the air, these hydrogen bonds occur between the top layer of water molecules to create a sort of film on the body of water (this is what allows insects such as pond skaters to float)
27
What is adhesion in the context of water?
Adhesion refers to the attraction of water molecules to other substances or surfaces due to hydrogen bonding
28
What is capillary action?
where water can rise up a narro tube against the forve of gravity
29
Why is water less dense in its solid form?
Hydrogen Bonding: Water molecules are polar, with a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. This polarity allows water molecules to form hydrogen bonds with each other.
Liquid Water: In the liquid state, water molecules are in constant motion, and they are relatively densely packed, held together by hydrogen bonds. These bonds are dynamic and constantly breaking and reforming.
Formation of Ice: When water freezes, the temperature decreases, causing the water molecules to slow down. As a result, the hydrogen bonds between the molecules become more stable and rigid.
Hexagonal Lattice Structure: The stable hydrogen bonds between water molecules in ice force them into a hexagonal lattice structure. In this structure, each water molecule is bonded to four others, creating open spaces between them.
Lower Density: The open spaces in the hexagonal lattice structure mean that a given volume of ice contains fewer water molecules compared to the same volume of liquid water. This results in a lower density for ice.
30
what doe carbohydrates contain?
what is the general formula?
carbon hydrogen and oxygen
C6H12O6
31
monosaccharide
single sugar unit
32
structure of an alpha glucose
hexose- six carbons
- OH is above the carbon one
33
beta glucose structure
- OH is below carbon one
34
are glucose polar or soluble? why?
- they are polar and soluble
- hydrogen bonds form between OH group and water
- so glucose can dissolve in the cytoplasm
35
condensation reaction of two glucose molecules
- when two alpha glucose are side by side the OH groups interact
- two hydrogens and one oxgen is removed from the glucose molecules to form a water molecule
- a glycosidic bond is formed (1,4)
36
fructose + glucose
sucrose
37
galactose + glucose
lactose
38
what is a pentose monosaccharide
contains five carbon atoms
39
what are the two components of starch?
amylose
amylopectin
40
what is amylose?
- it is a polysaccharide in starch
- monomer is alpha glucose
- it contains only 1-4 glycosidic bonds between alpha glucose molecules
- the long chain twists to form a helix further stabilised by hydrogen bonds within the molecule
-> making it compact and less soluble than individual glucose molecules
41
what is amylopectin?
- it is a polysaccharide in starch
- contains 1-4 and 1-6 glycosidic bonds
- it has a branched structure because of the 1-6 bonds
42
what is glycogen?
compare its structure to amylopectin?
- it is an energy storage molecule in animals an fungi
- it has both 1-4 and 1-6 glycosidic bonds
- it has more 1-6 than amylopectin so it has more branches
-> therefore it is more compact and need less space for storage
43
why are the features of glycogen important for its function as a energy store for animals?
- insoluble
- compact
- highly branched
-> the branching and coiling makes them compact which is good for storage as less space is needed
-> many free ends where molecules can be hydrolysed and added speeding up the process of storing r releasing glucose required by the cell
44
what is cellulose
explain its structure
- a polysaccharide made of beta glucose
- every alternate beta glucose is flipped so that the hydroxyl groups on carbon one and carbon 4 are close enough to react
- it is unable to coil or form branches so a straight chain is formed
45
explain the structure of cellulose fibres
- cellulose molecules form H bonds with others to form microfibrils
- microfibrils join to form macrofibrils
- macrofibrils join to form fibres
- the fibres are strong and insoluble
- used to make cell walls
46
explain a method to test for reducing sugars?
- Add Benedict's reagent (which is blue as it contains copper (II) sulfate ions. and an alkaline solution) to a sample solution in a test tube
- Heat the test tube in a water bath or beaker of water that has been brought to a boil for a few minutes
- If a reducing sugar is present, a coloured precipitate will form as copper (II) sulfate is reduced to copper (I) oxide which is insoluble in water
- It is important that an excess of Benedict’s solution is used so that there is more than enough copper (II) sulfate present to react with any sugar present
blue -> brick red
Cu2+ -> Cu+
A positive test result is a colour change scale from blue (no reducing sugar), through green, yellow and orange (low to medium concentration of reducing sugar) to brown/brick-red (a high concentration of reducing sugar)
This test is semi-quantitative as the degree of the colour change can give an indication of how much (the concentration of) reducing sugar present
47
what is a reducing sugar?
a sugar that acts as a reducing agent
- it donates electrons in a reaction and reduce another molecule
- all monosaccharides and some disaccharides are reducing sugars
48
how to test for non-reducing sugars?
what happens if you add HCl
- they dot react with benedict's solution so the solution will remain blue as the copper ions have not been reduced
- if sucrose is boiled with HCl then it will give a positive result. because if has been hydrolysed to form to reducing sugars (glucose and fructose)
49
what is iodine used to test
the presence of starch
50
how do you test for starch?
- add a few drops of yellow/brown iodine in potassium iodide solution to the sample
-The iodine is in potassium iodide solution as iodine is insoluble in water
- If starch is present, iodide ions in the solution interact with the centre of starch molecules, producing a complex with a distinctive blue-black colour
| hi
51
what do lipids contain
C, H., O
52
compare the states of fats and oils ate at RTP
fats are solid
oils are liquids
53
are lipids polar?
no
- they are non-polar as electrons in bonds are shared evenly between bonded atoms
- have no delta + or delta -
54
are lipids soluble, why?
no
- they are non-polar molecules
55
what is the structure of a triglyceride
- contains one glycerol (alcohol) molecule bonded to 3 fatty acids (carboxylic acid)
- the H from three hydroxyl groups of the glycerol molecule reacts with the OH from three fatty acids COOH group
- this forms an ester
+ 3H2O
56
what is a saturated fatty acid
fatty acid chain with no carbon carbon double bonds
57
what is an unsaturated fatty acid
how does this effect the molecule
contains carbon carbon double bonds
- is causes it to bend or kink, therefore they cannot pack closely together - so the are liquid at RTP and called oils
58
what are phospholipids
instead of a fatty acid chain they have a phosphate group
- contains two fatty acids one glycerol molecule and a pphosphate group
PO4 3-
- they have a non-polar end/tail (the fatty acid chains) which are hydrophobic
- polar end/head (the phosphate group) they are hydrophilic
59
what is a sterol?
- a lipid that contains four carbon rings
- they have an OH- at one end
- so they have one polar and hydrophilic and and hydrophobic for the rest of the molecule
60
what is cholesterol
it is a sterol
- manufactured in the liver and intestines
- it is important for the formation of cell membranes
61
lipid roles
- membrane formation and the creation of hydrophilic barriers
- hormone production
electrical insulation for nerve impulse transmission
- waterproofing
62
roles of triglycerides
- thermal insulation to reduce heat loss
- cushioning to protect vital organs such as hearts
- buoyancy for aquatic animals
63
how to identify lipids
- emulsion test
- mix sample with ethanol
then mix with water and shake
- if white emulsion forms as a layer on top then sample contains lipids
64
what are amino acids?
- made of C,H, O and N
- monomer of proteins/peptides
R
|
COOH--C----NH2
|
H
- has a carboxylic acid group and an amine group
- the variable group changes depending on AA
65
how are peptides made
the amine and the carboxylic acid group react, specifically the hydrogen and OH respectively
-a peptide bond is formed and a water molecule is lost
66
what is a polypeptide
when many AA are joined together by peptide bonds
67
what is peptidyl transferase
an enzyme that catalyses the reaction of formng a peptide bond
- it is present in ribosomes
68
what is the enzyme that catalyses the formation of a peptide chain
peptidyl transferase
69
state the levels of protein structure
primary
secondary
tertiary
quaternary
70
Secondary structure
The secondary structure of a protein occurs when the weak negatively charged nitrogen and oxygen atoms interact with the weak positively charged hydrogen atoms to form hydrogen bonds
There are two shapes that can form within proteins due to the hydrogen bonds:
α-helix
β-pleated sheet
The secondary structure only relates to hydrogen bonds forming between the amino group and the carboxyl group (the ‘protein backbone’)
The hydrogen bonds can be broken by high temperatures and pH changes
70
Primary structure
- The sequence of amino acids bonded by peptide bonds
- The DNA of a cell determines the primary structure of a protein by instructing the cell to add certain amino acids in a certain sequence. This affects the shape and therefore the function of the protein
71
α-helix
The α-helix shape occurs when the hydrogen bonds form between every fourth peptide bond (between the oxygen of the carboxyl group and the hydrogen of the amine group)
A coil shape is formed
72
β-pleated sheet
- when polypeptide chains lie next to each other they can join by hydrogen bonds between the molecules
- forming sheet like structures that are pleated
73
Tertiary structure
the final folding of the protein
additional bonds form between the R groups (side chains)
The additional bonds are:
Hydrogen (these are the weakest)
Disulphide (only occurs between R-groups containing sulfur. They are covalent and are the strongest bond)
Ionic (occurs between oppositely charged R groups)
Weak hydrophobic interactions (between non-polar and polar R groups)
74
Quaternary
the association of two or more individual proteins known as subunits
-> have the same interactions as the tertiary structure but are between different protein molecules
- haemoglobin is an example
75
Globular Proteins feautures
Globular proteins are compact, roughly spherical (circular) in shape and soluble in water
76
globular proteins structure
- Globular proteins form a spherical shape when folding into their tertiary structure because:
-their non-polar hydrophobic R groups are orientated towards the centre of the protein away from the aqueous surroundings and
-their polar hydrophilic R groups orientate themselves on the outside of the protein
- This orientation enables globular proteins to be (generally) soluble in water as the water molecules can surround the polar hydrophilic R groups
77
Globular proteins functions
give an example
The solubility of globular proteins in water means they play important physiological roles as they can be easily transported around organisms and be involved in metabolic reactions
78
Insulin as a protein
- Insulin is a globular protein produced in the pancreas. It plays an important role in the control of blood glucose concentration
- needs to be transported in the blood so is a soluble molecule
79
conjugated proteins structures
give an examples
- are globular proteins that contain a non-protein component a prosthetic group
- prosthetic groups can be lipids or carbohydrates that combine to form lipoproteins or glycoproteins
- metal ions or molecules from vitamins can be prosthetic groups
haemoglobin
80
Haemoglobin
- is an oxygen-carrying pigment found in red blood cells (it is globular and conjugated protein)
- It has a quaternary structure as there are four polypeptide chains. These subunits are globin proteins (two α–globins and two β–globins) and each subunit has a prosthetic haem group
- The prosthetic haem group contains an iron II ion (Fe2+) which is able to reversibly combine with an oxygen molecule forming oxyhaemoglobin and results in the haemoglobin appearing bright red
81
Catalase as a protein
- it is a conjugate protein
- it is a quaternary protein with 4 haem subunits
- Iron II allows catalase to interact with H2O2 hydrogen peroxide
- H2O2 is a by-product of metabolism and damaging to cells
82
Fibrous Proteins
formed from long insoluble molecules due to a large number of hydrophobic R groups
They contain a limited range of AA, usually with small R-groups
The AA sequences is quite repetitive so it forms very organised structures
they tend to make strong long molecules that arent usually folded into 3D shapes like globular
83
Keratin
- a group of fibrous proteins
- present in hair, skin and nails
- has a large proportion of sulphur containing AAs like cysteine
-> this forms many disulphide bonds forming strong inflexible materials
- more disulphide bonds the less flexible
84
Elastin
- a fibrous protein found in elastic fibres
- present in blood vessels and alveoli
- give structures flexibility to expand if needed but also can return to normal size
- it is a quaternary protein made of stretchy molecules called tropoelastin
85
Collagen
- a fibrous protein
- a connective tissue found in skin, tendons, ligaments and nervous system
- made of 3 polypeptides wound in a long rope like structure
86
types of nucleic acid
DNA and RNA
87
what are nucleic acids
contain C, H, O, N and P
- they are large polymers formed from many nucleotides joined together by a phosphodiester bond
88
Nucleotide structure
A pentose sugar (a sugar with 5 carbon atoms)
A nitrogen-containing organic base (one or two carbon rings)
A phosphate group PO4 2-
89
structure of nucleic acids
- Separate nucleotides are joined together via condensation reactions
- the phosphate group on carbon 5 covalently bonds with the OH group of carbon 3 on another nucleotide
- this forms a phosphodiester bond
- this forms a long strong sugar-phosphate backbone with a base attached to each sugar
90
DNA vs RNA
the pentose sugar has one fewer oxygen atoms than ribose
91
types of bases
ATCG
pyrimidines
Purines
92
what are pyrimidines
bases with one carbon ring
- it is the smaller base
- thymine and cytosine
93
what are purines
bases with two carbon rings
- the larger bases
- adenine and guanine
94
how do bases bond to each other
pyrimidines always bond with purines
- A (2) & T (1)
- G (2) & C (1)
- A and T form two hydrogen bonds
- C and G form three hydrogen bonds
95
what is the double helix
- it is made of two polynucleotides oiled into a helix (DNA double helix)
- the strands are held by hydrogen bonds between bases
- strands run in opposite directions parallel, therefore they are anti-parallel (5' and 3')
96
explain base pairing rules
- adenine and thymine always bond together by 2 hydrogen bonds
- cytosine and guanine bond together by 3 hydrogen bonds
- so pyrimidines always bond with purines
- so the distance between the DNA backbone has a constant distance resulting in parallel chains
- it also means that there are equal amounts of A and T aswell as G and C
97
what is RNA
- it has a role in transferring genetic info from DNA to proteins
- DNA is too large so is converted to RNA
- RNA is different to RNA as its sugar is ribose not deoxyribose and thymine is replaced with uracil
- uracil also forms 2 hydrogen bonds with adenine
98
what is DNA replication?
Before a (parent) cell divides, it needs to copy the DNA contained within it
Doubling the DNA ensures that the two new (daughter) cells produced will both receive full copies of the parental DNA
DNA replication occurs in preparation for mitosis, when a parent cell divides to produce two genetically identical daughter cells – as each daughter cell contains the same number of chromosomes as the parent cell, the number of DNA molecules in the parent cell must be doubled before mitosis takes place
99
what is semi-conservative replication
The DNA is copied via a process known as semi-conservative replication (semi = half)
The process is called this because in each new DNA molecule produced, one of the polynucleotide DNA strands (half of the new DNA molecule) is from the original DNA molecule being copied
The other polynucleotide DNA strand (the other half of the new DNA molecule) has to be newly created by the cell (free nucleotides binding to complimentary bases)
Therefore, the new DNA molecule has conserved half of the original DNA and then used this to create a new strand
100
when does DNA replication occur
during the S phase of the cell cycle (which occurs during interphase, when a cell is not dividing)
101
steps of DNA replication
- The enzyme helicase unwinds the DNA double helix by breaking the hydrogen bonds between the base pairs on the two antiparallel polynucleotide DNA strands to form two single polynucleotide DNA strands
- Each of these single polynucleotide DNA strands acts as a template for the formation of a new strand made from free nucleotides that are attracted to the exposed DNA bases by base pairing
- The new nucleotides are then joined together by the enzyme DNA polymerase which catalyses condensation reactions to form a new strand
- The original strand and the new strand join together through hydrogen bonding between base pairs to form the new DNA molecule
- This method of replicating DNA is known as semi-conservative replication because half of the original DNA molecule is kept (conserved) in each of the two new DNA molecules
102
what is DNA polymerase
The new nucleotides are then joined together by the enzyme DNA polymerase which catalyses condensation reactions to form a new strand
it can only bind onto the 3' end, so travels in the 3' to 5' end
103
what happens because DNA polymerase only acts in one direction
- it can only bind to the 3' and travel towards the 5'
- this is an issue as DNA polymerase has to replicate both strands
- it is continuous replication f the strand that is unzipped from the 3' end - the leading strand
- the strand unzipped from the 5' end undergoes discontinuous replication. DNA polymerase waits until a section of the strand is unzipped and works backwards along the strand. so DNA is produced in sections called Okazaki fragments and have to be joined together - the lagging strand
104
Nature of the Genetic Code
- A gene is a sequence of nucleotides that forms part of a DNA molecule (one DNA molecule contains many genes)
- This sequence of nucleotides (the gene) codes for the production of a specific polypeptide (protein)
- Protein molecules are made up of a series of amino acids bonded together
- The shape and behaviour of a protein molecule depends on the exact sequence of these amino acids (the initial sequence of amino acids is known as the primary structure of the protein molecule)
- The genes in DNA molecules, therefore, control protein structure (and as a result, protein function) as they determine the exact sequence in which the amino acids join together when proteins are synthesised in a cell
105
the triplet code
- Each sequence of three bases (i.e. each triplet of bases) in a gene codes for one amino acid
- These triplets codes for different amino acids – there are 20 different amino acids that cells use to make up different proteins
- the genetic code is universal - all organisms use the same code
106
what is a gene
a section of DNA that contains the complete sequence of bases that code for an entire protein
107
degenerate code meaning
- multiple codons can code for the same amino acids
108
non-overlapping
The non-overlapping nature of the genetic code means that each base is only read once
The adjacent codons do not overlap
A non-overlapping code means that the same letter is not used for two different codons; in other words, no single base can take part in the formation of more than one codon
109
what is transcription
- in order for a protein to be synthesised, genetic information must leave the nucleus, through the cytoplasm to the ribosome. However DNA is too big to leave through the nuclear pores
- so, by transcription, the section of DNA that contains the gene is transferred to mRNA
110
explain the process of transcription
- Part of a DNA molecule unwinds (the hydrogen bonds between the complementary base pairs break)
- The exposed gene can then be transcribed (the gene from which a particular polypeptide will be produced)
- A complimentary copy of the code from the gene is made by building a single-stranded nucleic acid molecule known as mRNA (messenger RNA)
- Free RNA nucleotides pair up (via hydrogen bonds) with their complementary (now exposed) bases on one strand (the template strand) of the ‘unzipped’ DNA molecule
- The sugar-phosphate groups of these RNA nucleotides are then bonded together (by phosphodiester bonds) by the enzyme RNA polymerase to form the sugar-phosphate backbone of the mRNA molecule
- When the gene has been transcribed (when the mRNA molecule is complete), the hydrogen bonds between the mRNA and DNA strands break and the double-stranded DNA molecule re-forms
The mRNA molecule then leaves the nucleus via a pore in the nuclear envelope
110
what strand is copied during transcription
In the transcription stage of protein synthesis, free RNA nucleotides pair up with the exposed bases on the DNA molecule
RNA nucleotides only pair with the bases on one strand of the DNA molecule
This strand of the DNA molecule is known as the template strand (or the transcribed strand) and it is used to produce the mRNA molecule
The other strand is known as the coding strand (or the non-template or non-transcribed strand)
RNA polymerase moves along the template strand in the 3' to 5' direction
This means that the mRNA molecule grows in the 5' to 3' direction
Because the mRNA is formed by complementary pairing with the DNA template strand, the mRNA molecule contains the exact same sequence of nucleotides as the DNA coding strand (although the mRNA will contain uracil instead of thymine)
111
sense and antisense strand
- sense strand contains the gene it runs 5' to 3'
- antisense strand is a complementary copy of the sense strand and runs 3' to 5'
- the antisense is the template, so that the complementary RNA strand formed carried the same base sequences of the sense strand
112
Structure and Role of tRNA
- tRNA is single stranded. Like mRNA, tRNA is a single strand with the bases U, A, C, and G.
- tRNA is a cloverleaf shape. tRNA has a slightly different structure to mRNA. The single strand of tRNA is folded up into a cloverleaf shape.
-tRNA has two attachment sites. At one end of tRNA, there is an attachment site for amino acids. At the opposite end of tRNA, there is an attachment site for anti-codons.
- tRNA carries amino acids. We’ve seen that tRNA has attachment site for amino acids. During the process of translation, tRNA carries and transfers these amino acids to ribosomes
113
Steps of Translation
1. mRNA binds to the ribosome. mRNA binds to the ribosome. This binding is helped by the 5’ cap of the mRNA, which the ribosomes recognise and bind to.
2. The ribosome reads the first codons. The ribosome reads the codons on the mRNA, beginning with the start codon
3. A tRNA will bring the complementary amino acid for the first codon. Amino acids are found in the cytoplasm. Each specific tRNA has a complementary amino acid, and can bring it over. This is an ATP driven process.
4. Another tRNA brings the second amino acid. The ribosome continues to read the next codon, and another tRNA brings the correct amino acid.
5. The first tRNA leaves. The first tRNA is then released from the ribosome, and the second tRNA takes its place. This process is repeated for each codon that the ribosome reads.
6. A peptide bond forms. A peptide bond forms between the two amino acids. An enzyme called peptidyl transferase catalyses this
7. The process continues until a stop codon is reached.
8. After translation, the polypeptide chains are folded.
9. Polypeptides can also undergo post-translational modifications.
10. Proteins destined to leave the cell go to the rough ER.
11. Proteins destined to stay in the cell go to the cytoplasm.
114
The Need for Energy
Active transport
Exocytosis
Endocytosis
Anabolism
Cell division
Movement
115
structure of ATP
- a nitrogenous base (adenine)
- a pentose sugar (ribose)
- three phosphate groups
116
how does ATP release energy
- energy is needed to break bonds, but released when they are made
- small amounts of energy is needed to break the PO4 3- but a large amount of energy is released when the liberated phosphate undergoes bond forming reactions
- a hydrolysis reaction forming ADP
- this reaction happens in association with energy requiring reactions, they are coupled
117
Is ATP a good long term energy store
- the phosphate bonds are unstable
- fats and lipids are good long term store
118
ADP + Pi
condensation reaction
phosphorylation
119
why is ATP a good immediate energy store
- although not much atp is stored because of its instability, it can be constantly interconverted between ATP and ADP
120
properties of ATP
- small - can move easily between cells
- water soluble - energy requiring processes happen in aqueous solution
- contains bonds between phosphates with intermediate energy - energy isn't wasted
- releases energy in small quantities
- easily regenerated
