aqa a level biology topic 1

What is a monomer?

Monomers are the smaller units from which larger molecules are made.

What is a polymer?

Polymers are molecules made from a large number of monomers joined together.

what are the polymers of glucose?

starch, glycogen, cellulose

what is the polymer of amino acid?

protein

what are the polymers of nucleotides?

DNA and RNA

Name 3 monosaccharides

glucose, fructose, galactose

Name 3 dissacharides.

sucrose, lactose, maltose

Name 3 polysaccharides

starch, glycogen, cellulose

How are dissacharides formed?

made of two monosaccharides

joined together by a glycosidic bond

formed via a condensation reaction

How is maltose formed?

maltose is a disaccharide formed by condensation of two glucose molecules

How is sucrose formed?

sucrose is a disaccharide formed by condensation of a glucose molecule and a fructose molecule

How is lactose formed?

lactose is a disaccharide formed by condensation of a glucose molecule and a galactose molecule.

What is a condensation reaction?

A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water.

What is hydrolysis?

A hydrolysis reaction breaks a chemical bond between two molecules and involves the use of a water molecule.

How are polysaccharides formed?

Polysaccharides are formed by the condensation of many glucose units.

how are glycogen and starch formed?

Glycogen and starch are formed by the condensation of α-glucose.

How is cellulose formed?

Cellulose is formed by the condensation of β-glucose.

describe the structure and function of glycogen?

- animals cells get energy from glucose too, but animals, store excess glucose as glycogen.

Its structure has loads of side branches. This means that stored glucose can be released quickly, which is important for energy release in animals.

It's also very compact.

describe the structure and function of starch?

Cells get energy from glucose. Plants store excess glucose as starch. When it needs more glucose, it breaks down starch to release the glucose.

describe the structure and function of starch?

Amylose: long, unbranched chain of alpha-glucose arranged in a coiled structure. This makes the molecule compact, so it's really good for the storage of energy

describe the structure and function of starch?

Amylopectin: highly branched molecule that allows for the fast release of energy, as there are many points available for enzymes to act on

-Starch is insoluble, too large to leave the cell and good for storage

describe the structure and function of cellulose?

1} Cellulose is made of long, unbranched chains of beta glucose.

2) When beta-glucose molecules bond, they form straight cellulose chains.

describe the structure and function of cellulose?

3) The cellulose chains are linked together by hydrogen bonds to form strong fibres called microfibrils. The strong fibres mean cellulose provides structural support for cells (e.g. in plant cell walls).

Name and outline the test for reducing sugars

- Add Benedict's reagent (which is blue) to a sample, and heat it in a water bath that's been brought to the boil

- If the tests positive it will form a coloured precipitate

- it should change from blue to green, yellow, orange and red

- Reducing sugar a include all monocharides and some disaccharides (maltose and lactose)

Outline the test for non- reducing sugars

- break it down into monosaccharides

- to do this you get a new sample of the test solution, add dilute hydrochloride acid and heat it it in a water batht that's been brough to the boil.

Outline the test for non- reducing sugars

You then neutralise it with sodium hydrogen carbonate.

The carry out the Benedict's test. It the test positive it will form a coloured precipitate. If negative the solution will stay blue, so it doesn't contain any sugar.

Outline the test for starch

A chemical test for starch is to add iodine solution to food (yellow/brown) and look for a colour change. In the presence of starch, iodine turns a blue/black colour

How are triglycerides formed?

Triglycerides are formed by the condensation of one molecule of glycerol and three molecules of fatty acid.

A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond.

What is a saturated fatty acid?

The hydrocarbon chain has only single bonds between carbons

What is a unsaturated fatty acid?

the hydrocarbon chain has at least one double bond between carbons.

describe the properties of triglycerides?

•High ratio of energy storing carbon-hydrogen bonds to carbon atoms and therefore they are an excellent energy store.

• A low mass to energy ratio meaning that they are a good storage molecule, with a lot of energy being stored in a small volume. This is beneficial for animals as it is less mass to move around.

describe the properties of triglycerides?

• Being large and non-polar lipids are insoluble in water and therefore their storage does not affect the water potential of cells.

describe the properties of triglycerides?

• A high ratio of hydrogen-oxygen atoms means that triglycerides release water when they are oxidised and therefore provide and important source of water for organisms to live in dry environments.

Describe the emulsion test.

The procedure is for the sample (food) to be suspended in ethanol, allowing lipids present to dissolve (lipids are soluble in alcohols). The liquid (alcohol with dissolved fat) is then decanted into water.

What is a phospholipid?

In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-containing group.

describe the properties of phospholipids?

Phosphate heads are hydrophilic (loves water) and the tails are hydrophobic (hates water)

hydrophilic head can attract water as its charged

due to the phosphate being charged it repels other fats

describe the properties of phospholipids?

the fatty acid chain is not charged, its known as the hydrophobic tail and it repels water but will mix with fats.

2 charged regions so they are polar

• In an aqueous environment being polar means a bilayer can be formed which make up the plasma membrane around the cells

What are proteins?

- The monomers of proteins are amino acids

- A dipeptide is formed when two amino acids join together

- A polypeptide is formed when more than two amino acids join together

- Proteins are made up of one or more polypeptides

describe how amino acids are joined together to form a dipeptide?

Dipeptides are formed by the condensation of two amino acids. peptide bond forms between OH of carboxyl group and H of amine group.

Describe the primary structure of a protein

order and number of amino acids in a protein.

Describe the secondary structure of a protein

The polypeptide the amino acids in the chain. This makes it automatically coil into an alpha (a) helix or fold into a (b) pleaded sheet.

Describe the tertiary structure of a protein

Tertiary structure

- is when the coiled or folded chain of amino acids is often coiled and folded further. More binds form between different parts of the polypeptide chain, including hydrogen bonds and ionic bonds (attractions between negative and positive charges on different parts of the molecule)

Describe the tertiary structure of a protein

Disulfide bridges also form whenever two molecules of the amino acid cysteine come closer- the sulcus atom in one cysteine bonds to the soulful atom in the other. For proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure.

Describe the quaternary structure of a protein

Some proteins are made of several polypeptide chains held together by bonds. The quaternary structure is The way these polypeptide chains are assembled together. For proteins made from more than one polypeptide (haemoglobin, insulin, collagen), the quaternary structure is the proteins final 3D structure.

functions of proteins

1. Structural Support:

Proteins form the structural framework of cells and tissues, providing shape and support.

Examples include collagen in skin and tendons, and keratin in hair and nails.

functions of proteins

5. Antibodies:

Antibodies are proteins that recognize and neutralize foreign invaders, like bacteria and viruses, as part of the immune system.

Functions of proteins

Transport:

Proteins transport substances across cell membranes and throughout the body.

Examples include hemoglobin, which carries oxygen in the blood, and ferritin, which transports and stores iron.

Functions of proteins

Proteins called enzymes act as biological catalysts, speeding up chemical reactions within the body.

They are essential for digestion, breaking down food into smaller molecules that can be absorbed.

Enzymes are involved in a wide range of metabolic processes.

what is the test for proteins

The Biuret test

1. Place the sample to be tested in a test tube and add an equal volume of sodium hydroxide at room temperature.

2. Add a few drops of very dilute (0.05%) copper (II) sulfate soliton and mix gently.

what is the test for proteins

3. A purple colouration indicates the presence of a peptide bond and hence a protein. A negative result would mean the solution remains blue.

What are enzymes and describe the specificity and properties relating to the tertiary structure.

1) Enzymes catalyse metabolic reactions-

2) they can affect structures in an organism (e.g. enzymes are involved in the production of collagen, an important protein in the connective tissues of animals) as well as functions of animals (like respirations)

3) they can be intracellular- within cells or extracelluar (outside cells)

What are enzymes and describe the specificity and properties relating to the tertiary structure.

4) they are proteins

5) they have an active site, which has an specific shape. The active site is the part of the enzyme where the substrate molecules (the substance that the enzyme interacts with) binds to.

6) enzymes are highly specific due to their tertiary structure

How do enzymes speed up chemical reactions?

Enzymes increase rate of reaction by lowering the activation energy of the reaction they catalyse.

Describe the lock and key model

1. Substrate collides with the active site of an enzyme

2. Substrate binds, enzyme-substrate complex forms

3. Substrate converted to products

4. Products released from the active site which is now free to bind to another substrate

Describe the induced fit model of enzyme action

Active site / enzyme not complementary;

Active site changes (shape) / is flexible;

(Change in enzyme allows) substrate to fit / E-S complex to form;

what factors affect the rate of enzyme controlled reactions?

Temperature

ph

substrate and enzyme concentration

inhibitors

what is the effect of temperature on enzymes?

1) The rise in temperature makes the enzyme's molecules vibrate more.

2) If the temperature goes above a certain level, this vibration breaks some of the bonds that hold the enzyme in shape.

what is the effect of temperature on enzymes?

3) The active site changes shape and the enzyme and substrate no longer fit together.

4) At this point, the enzyme is denatured — it no longer functions as a catalyst.

what is the effect on ph on enzymes?

pH affects the enzymes shape as it can disrupt the bonds in the tertiary structure of the enzyme which changes the active site

enzyme denatures and fewer E-S complexes form

what are the effects of substrate concentration on enzymes?

as concentration of substrate increases, rate of reaction increases as more enzyme-substrate complexes are formed. However, beyond a certain point the rate of reaction no longer increases as enzyme concentration becomes the limiting factor.

the rate of reaction increases as enzyme concentration increases as there are more active sites for substrates to bind to, however increasing the enzyme concentration beyond a certain point has no effect on the rate of reaction

what are the effects of enzyme concentration on enzymes?

as there are more active sites than substrates so substrate concentration becomes the limiting factor.

What are competitive inhibitors?

Competitive inhibitors are molecules that are similar to substrates and bind to the active site. this prevents substrate from binding, a higher substrate concentration can override this.

What are non-competitive inhibitors?

bind to enzymes away from active sites, the allosteric site.

this causes the active site to change shape so substrate cannot bind regardless of substrate concentration

What is DNA? Describe its function

A DNA molecule is a double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs.

deoxyribonucleic acid codes for the sequence of amino acids in the primary structure of a protein which determines the final 3D structure and function of a protein

What is the structure of DNA nucleotide?

DNA is a polymer of a nucleotide.

The components of a DNA nucleotide are deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine.

What are polynucleotides?

polymers of nucleotides

created via a condensation reaction between the deoxyribose sugar and the phosphate group creating a phosphodiester bond.

phosphodiester bond are strong covalent bonds and therefore ensures the genetic code isn't broken down

How is the double helix formed?

hydrogen bonding occurs between complementary bases

A-T forms two hydrogen bonds

C-G forms three hydrogen bonds

this is important as it helps maintains the order of the genetic code when DNA replicates

how does the structure of DNA relates to its function?

stable structure due to sugar phosphate backbone

double stranded so replication can occur using one strand as template

how does the structure of DNA relates to its function?

weak hydrogen bonds for easy unzipping of the two strands in a double helix during replication

large molecule to carry lots of information

complementary base pairing which allows identical copies to be made

What is RNA? Describe its structure.

ribonucleic acid is a polymer of a nucleotide formed of a ribose sugar, nitrogenous base and a phosphate group.

it has the same bases as dna except the thymine is replaced with uracil

An RNA molecule is a relatively short polynucleotide chain.

what is the function of RNA

to copy and transfer the genetic code for DNA in the nucleus to the ribosomes

Ribosomes are formed from RNA and proteins.

what are the three types of RNA?

mRNA, tRNA, rRNA

What is mRNA and what does it do?

copy of a gene from DNA

created in the nucleus and then leaves to carry the copy of the genetic code of one gene to a ribosome in the cytoplasm

Why is mRNA necessary rather than DNA?

DNA is too large to leave the nucleus and would be at risk of being damaged by enzymes.

mRNA is much shorter as it only has the length of one gene and can leave the nucleus

mRNA is short lived and single stranded and has codons

what tRNA and describe its structure and function

found in cytoplasm

it is single stranded but folds into a clover leaf which is held by hydrogen bonds

the function of tRNA is to attach to one of the 20 amino acids and transfer the amino acid to the ribosome to create a polypeptide chain

What is an anticodon?

specific amino acids attach to specific tRNA molecules and this is determine by 3 bases found on tRNA which is complementary to the 3 bases found on mRNA

these are called anticodons as they are complementary to the codon on mRNA

What is rRNA?

Ribosomal RNA

What are the differences between DNA and RNA monomers?

DNA contains thymine but RNA contains uracil

DNA contains deoxyribose but RNA contains ribose

what are the differences between DNA and RNA polymers?

DNA is much longer

DNA is double stranded, RNA is single stranded

What is DNA replication?

the process of dna replication semi conservative

before cells divide all the DNA must replicate

describe the process of semi conservative replication?

DNA helicase breaks the hydrogen bonds between between complementary bases in the polynucleotide strands. this causes the double helix to unwind

each strand acts as a template

free floating nucleotides are attracted to their complementary bases

adjacent nucleotides are joined together by DNA polymerase by condensation reaction forming a phosphodiester bond.

how does DNA polymerase move oppositely along an antiparallel strand?

The active site of DNA polymerase is only complementary to the 3' end of the newly forming DNA strand — so the enzyme can only add nucleotides to the new strand at the 3' end. This means that the new strand is made in a 5' to 3' direction and that 3'- DNA polymerase moves down the template strand in a 3' to 5' direction.

Because the strands in the double -helix are antiparallel, the D N A polymerase working on one of the template strands moves in the opposite direction to the DNA polymerase working on the other template strand.

who discovered the structure of DNA

Watson and Crick

What was the Meselson-Stahl experiment?

1) Two samples of bacteria were grown — one in a nutrient broth containing light nitrogen, and one in a broth with heavy nitrogen. As the bacteria reproduced, they took up nitrogen from the broth to help make nucleotides for new DNA. So the nitrogen gradually became part of the bacteria's DNA.

2) A sample of DNA was taken from each batch of bacteria, and spun in a centrifuge. The DNA from the heavy nitrogen bacteria settled lower down the centrifuge tube than the DNA from the light nitrogen bacteria — because it's heavier.

3) Then the bacteria grown in the heavy nitrogen broth were taken out and put in a broth containing only light nitrogen. The bacteria were left for one round of DNA replication, and then another DNA sample was taken out and spun in the centrifuge.

4) If re plication was conservative, the original heavy DNA, which would still be together, would settle at the bottom and the new light DNA would settle at the top.

5) If replication was semi-conservative, the new bacterial DNA molecules would contain one strand of the old DNA containing heavy nitrogen and one strand of new DNA containing light nitrogen. So the DNA would settle out between where the light nitrogen DNA settled out and where the heavy nitrogen DNA settled out.

6) As it turned out, the DNA settled out in the middle, showing that the DNA molecules contained a mixture of heavy and light nitrogen. The bacterial DNA had replicated semi-conservatively in the light nitrogen.

What is ATP?

A single molecule of adenosine triphosphate (ATP) is a nucleotide derivative and is formed from a molecule of ribose, a molecule of adenine and three phosphate groups.

How is ATP made?

during respiration from ADP+pi using ATP synthase

can be hydrolysed by ATP hydrolyase

1) W hen energy is needed by a cell, ATP is broken down into ADP and Pi .

2) This is a hydrolysis reaction. A phosphate bond is broken and energy is released. The reaction is catalysed by the enzyme ATP hydrolase.

How is ATP made?

3) ATP hydrolysis can be 'coupled' to other energy-requiring reactions in the cell — this means the energy released can be used directly to make the coupled reaction happen, rather than being lost as heat.

How is ATP made?

4) The released inorganic phosphate can also be put to use — it can be added to another compound (this is known as phosphorylation), which often makes the compound more reactive.

How is ATP made?

5) ATP can be re-synthesised in a condensation reaction between ADP and Pi This happens during both respiration and photosynthesis, and is catalysed by the enzyme ATP synthase

how does ATP act as an immediate source of energy

hydrolysis of ATP releases a small amount of energy by breaking a single bond in the phosphate group

The inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate other compounds, often making them more reactive.

what are the properties of ATP?

releases small manageable amounts of energy

small and soluble so easily transported around the cell

releases energy immediately

can phosphorylate other substances making the more reactive by transferring one of its phosphate groups

cant pass out of the cell so the cell has an immediately supply of energy