Biological molecules

Question 1

What are monomers?

Answer 1

Monomers are the smaller units from which larger molecules are made

Question 2

what are polymers?

Answer 2

Polymers are multiple repeating units of monomers

Question 3

what is a condensation reaction?

Answer 3

the joining of two monomers with the formation of a covelant bond involving the elimination of a molecule of water

Question 4

what is a hydrolysis reaction?

Answer 4

the breaking of a covenant bond between two monomers using a molecule water

Question 5

what are disaccharides and how are they formed?

Answer 5

Two monosaccharides joined together with a glycosidic bond, formed by a condensation reaction therefore releasing a molecule of water

Question 6

What is the special bond that is formed during the condensation reaction between two monosaccharides?

Answer 6

A glycosidic bond

Question 7

what are monosaccharides and give 3 examples?

Answer 7

monomers form which larger molecules form carbohydrates: glucose, galactose and fructose

Question 8

what are disaccharides and how are they formed?

Answer 8

two monosaccharides joined together with a glycosidic bond, formed by a condensation reaction, therefore releasing a molecule of water

Question 9

list 3 disaccharides and the monomers from which they are formed

Answer 9

Maltose = glucose ×2
Lactose = glucose + galactose
Sucrose = glucose + fructose

Question 10

What are polysaccharides and how are they formed

Answer 10

Many monosaccharides joined together with glycosidic bonds formed by a condensation reaction

Question 11

describe the structure of starch

Answer 11

-Made of alpha glucose
Amylose= is lo g and unbranded and forms a coiled shape
Amylopectin= is long and branched due to the 1-6 glycosidic bonds

Question 12

what is the properties of starch?

Answer 12

Amylose- the coiling makes it compact and acts as storage in smaller places
Amylopectin- branches increase the surface are for enzymes to hydrolyse glycosidic bonds allowing glucose to be releases quickly

Question 13

what are the uses for starch?

Answer 13

.plants use starch to store excess glucose as it is too large to leave cells and it is insoluble
.starch can be hydrolysed to release glucose for respiration

Question 14

describe the structure to glycogen

Answer 14

Made of alpha glucose
-is long and branched with side branches with 1-6 glycosidic bonds

Question 15

what are the properties of glycogen?

Answer 15

losts of branches increase the surface area for enzymes to hydrolyse glycosidic bonds allowing a faster release of glucose. It also is a compact molecule and so allows for storage

Question 16

what is the use for glycogen?

Answer 16

Animals store excess glucose as glycogen in muscles and in the liver and is therefore an energy store as it can be hydrolysed to release glucose quickly when needed for respiration

Question 17

describe the structure of cellulose

Answer 17

Made from beta glucose
-long unbranded straight chains with 1-4 glycosidic bonds and the chains are linked together by hydrogen bonds between the glucose molecules which form microfibrills

Question 18

what are the properties of cellulose

Answer 18

the hydrogen bonds between the cellulose chains make the microfibrills strong and flexible allowing them to provide support

Question 19

what are the uses of cellulose?

Answer 19

provides structural support in the cell walls of plants allowing them to become turgid

Question 20

what can polysaccharides be formed from?

Answer 20

glucose monomers that ate joined by 1-4 or 1-6 glycosidic bonds

Question 21

describe the test for reducing sugars

Answer 21

reducing sugars= monosaccharides, maltose and Lactose

1, add benedicts solution to sample
2, heat in a water bath
3, positive result = green, yellow, orange, red precipitate

Question 22

describe the test for non reducing sugars

Answer 22

non reducing sugars = sucrose

1, do benedicts test an stays blue
2, heat in water bath with acid
3, neutralise with an alkaline
4, heat in water bath with benedicts solution
5, positive= green, yellow, orange, red precipitate

Question 23

suggest the method to measure the quantity of sugar in a solution

Answer 23

carry out the benedicts test then filter and dry the precipitate then find the mass

Question 24

What is the structure of both α-glucose and β glucose?

Answer 24

They both have 6 carbon atoms, α-glucose has its OH group attached at the bottom right and β glucose has its OH group attached at the top right.

Question 25

What is the test for reducing sugars?

Answer 25

- Add test sample to Benedict's Reagent. - Heat it gently - If solution turns brick red, then a reducing sugar is present. - If the solution stays blue, then no reducing sugar is present.

Question 26

What is the test for non-reducing sugars?

Answer 26

After the test for reducing sugars, you should: - Add dilute hydrochloric acid to the test sample (hydrolyse the polysaccharides/disaccharides into its constituent monosaccharides) - Then add sodium hydrogencarbonate to neutralise the acid. (Benedict's reagent does not work in acidic conditions) - Add the sample to Benedict's reagent and then heat the sample. -If the solution turns brick red then a non-reducing sure is present. If the solution stays blue then there isn't a non-reducing or reducing sugar present.

Question 27

describe the structure of a fatty acid (RCOOH)

Answer 27

variable R group- hydrocarbon chain (saturated or unsaturated) COOH- carboxyll group

Question 28

describe how a triglyceride is formed

Answer 28

a condensation reaction between 1 glycerol molecule and 3 fatty acids which removes 3 molecules of water forming 3 ester bonds

Question 29

explain of the properties of triglycerides link to their function

Answer 29

-high ratio of C-H bonds to carbon atoms in hydrocarbon chain so they are used in respirationas they release more energy -hydrophobic / non-polar fatty acids so they are insoluble in water so they have no effect on water potential of cell or can be used as waterproofing

Question 30

describe the formation of a phospholipid

Answer 30

A condensation reaction reaction between a glycerol molecule, a phosphate group and 2 fatty acids forming an ester bond between the glycerol molecule and 2 fatty acid chains

Question 31

describe how the properties of phospholipids relate to their function

Answer 31

they form a bilayer in the cell membrane allowing for diffusion of lipid soluble or very small substances and restrict the movement of larger molecules and water soluble substances -phosphate heads are hydrophilic and so attract water -fatty acid tails are hydrophobic so repell the water

Question 32

describe the test for lipids

Answer 32

1, add ethanol, shake then add water 2, positive test is a milky emulsion

Question 33

What is a saturated fatty acid?

Answer 33

They dont contain any double bonds between their carbon atoms

Question 34

What are lipids?

Answer 34

they are not polymers, they contain hydrogen and carbon atoms. Lipids are a source of energy that help to insulate organisms and act as waterproofing

Question 35

What is an unsaturated fatty acid?

Answer 35

THey contaain a carbon-carbon double bond, meaning they contain fewer hydrogen atoms

Question 36

What bond is formed in triglycerides?

Answer 36

ester bond formed between each of the three OH groupson the glycerol and OH group on each fatty acid chain

Question 37

what bond is formed in phospholipids?

Answer 37

ester bond between two OH groups n the glycerol and OH group of each fatty acid chain.

Question 38

Describe the role of micelles in the absorption of fats into the cells lining the ileum.

Answer 38

Micelles include bile salts and fatty acids which make the fatty acids soluble in water For lipids to carry fatty acids to the lining of the ileum, maintaining a higher concentration of fatty acids to the lining of the ileum for the fatty acids to be absorbed by diffusion

Question 39

Expalin the arrangement of phospholipids in a cell surface membrane.

Answer 39

It forms a bilayer, with hyrophillic phosphate heads that are attracted to water, hydrophobic tails that face way from the water

Question 40

Describe how amino acids join together

Answer 40

● Condensation reaction ● Removing a water molecule ● Between carboxyl / COOH group of one and amine / NH2 group of another ● Forming a peptide bond

Question 41

What are dipeptides and polypeptides?

Answer 41

● Dipeptide - 2 amino acids joined together ● Polypeptide - many amino acids joined together

Question 42

Describe the primary structure of a protein

Answer 42

Sequence of amino acids in a polypeptide chain, joined by peptide bonds

Question 43

Describe the secondary structure of a protein

Answer 43

● Folding (repeating patterns) of polypeptide chain eg. alpha helix / beta pleated sheets ● Due to hydrogen bonding between amino acids ● Between NH (group of one amino acid) and C=O (group)

Question 44

Describe the tertiary structure of a protein

Answer 44

● 3D folding of polypeptide chain ● Due to interactions between amino acid R groups (dependent on sequence of amino acids) ● Forming hydrogen bonds, ionic bonds and disulfide bridges

Question 45

Describe the quaternary structure of a protein

Answer 45

● More than one polypeptide chain ● Formed by interactions between polypeptides (hydrogen bonds, ionic bonds, disulfide bridges)

Question 46

How do enzymes act as biological catalysts?

Answer 46

● Each enzyme lowers activation energy of reaction it catalyses ● To speed up rate of reaction

Question 47

Describe the induced-fit model of enzyme action

Answer 47

1. Substrate binds to (not completely complementary) active site of enzyme 2. Causing active site to change shape (slightly) so it is complementary to substrate 3. So enzyme-substrate complex forms 4. Causing bonds in substrate to bend / distort, lowering activation energy

Question 48

Describe how models of enzyme action have changed over time

Answer 48

● Initially lock and key model (now outdated) ○ Active site a fixed shape, complementary to one substrate ● Now induced-fit model

Question 49

Explain the specificity of enzymes

Answer 49

● Specific tertiary structure determines shape of active site ○ Dependent on sequence of amino acids (primary structure) ● Active site is complementary to a specific substrate ● Only this substrate can bind to active site, inducing fit and forming an enzyme-substrate complex

Question 50

Describe and explain the effect of enzyme concentration on the rate of enzyme-controlled reactions

Answer 50

● As enzyme conc. increases, rate of reaction increases ○ Enzyme conc. = limiting factor (excess substrate) ○ More enzymes so more available active sites ○ So more enzyme-substrate (E-S) complexes form ● At a certain point, rate of reaction stops increasing / levels off ○ Substrate conc. = limiting factor (all substrates in use)

Question 51

Describe and explain the effect of substrate concentration on the rate of enzyme-controlled reactions

Answer 51

● As substrate conc. increases, rate of reaction increases ○ Substrate conc. = limiting factor (too few enzyme molecules to occupy all active sites) ○ More E-S complexes form ● At a certain point, rate of reaction stops increasing / levels off ○ Enzyme conc. = limiting factor ○ As all active sites saturated / occupied (at a given time)

Question 52

Describe and explain the effect of temperature on the rate of enzyme-controlled reactions

Answer 52

● As temp. increases up to optimum, rate of reaction increases ○ More kinetic energy ○ So more E-S complexes form ● As temp. increases above optimum, rate of reaction decreases ○ Enzymes denature - tertiary structure and active site change shape ○ As hydrogen / ionic bonds break ○ So active site no longer complementary ○ So fewer E-S complexes form

Question 53

Describe and explain the effect of pH on the rate of enzyme-controlled reactions

Answer 53

● As pH increases / decreases above / below an optimum, rate of reaction decreases ○ Enzymes denature - tertiary structure and active site change shape ○ As hydrogen / ionic bonds break ○ So active site no longer complementary ○ So fewer E-S complexes form

Question 54

Describe and explain the effect of concentration of competitive inhibitors on the rate of enzyme-controlled reactions

Answer 54

● As concentration of competitive inhibitor increases, rate of reaction decreases ○ Similar shape to substrate ○ Competes for / binds to / blocks active site ○ So substrates can’t bind and fewer E-S complexes form ● Increasing substrate conc. reduces effect of inhibitors (dependent on relative concentrations of substrate and inhibitor)

Question 55

Describe and explain the effect of concentration of non-competitive inhibitors on the rate of enzyme-controlled reactions

Answer 55

● As concentration of non-competitive inhibitor increases, rate of reaction decreases ○ Binds to site other than the active site (allosteric site) ○ Changes enzyme tertiary structure / active site shape ○ So active site no longer complementary to substrate ○ So substrates can’t bind so fewer E-S complexes form ● Increasing substrate conc. has no effect on rate of reaction as change to active site is permanent

Question 56

Describe the basic functions of DNA

Answer 56

Holds genetic information which codes for polypeptides (proteins)

Question 57

Describe the basic functions of RNA

Answer 57

Transfers genetic information from DNA to ribosomes

Question 58

Describe how nucleotides join together to form polynucleotides

Answer 58

● Condensation reactions, removing water molecules ● Between phosphate group of one nucleotide and deoxyribose/ribose of another ● Forming phosphodiester bonds

Question 59

Describe the structure of DNA

Answer 59

● Polymer of nucleotides (polynucleotide) ● Each nucleotide formed from deoxyribose, a phosphate group and a nitrogen-containing organic base ● Phosphodiester bonds join adjacent nucleotides ● 2 polynucleotide chains held together by hydrogen bonds ● Between specific complementary basepairs - adenine / thymine and cytosine / guanine ● Double helix

Question 60

Describe the structure of (messenger) RNA

Answer 60

● Polymer of nucleotides (polynucleotide) ● Each nucleotide formed from ribose, a phosphate group and a nitrogen-containing organic base ● Bases - uracil, adenine, cytosine, guanine ● Phosphodiester bonds join adjacent nucleotides ● Single helix

Question 61

Suggest how the structure of DNA relates to its functions

Answer 61

● Two strands → both can act as templates for semi-conservative replication ● Hydrogen bonds between bases are weak → strands can be separated for replication ● Complementary base pairing → accurate replication ● Many hydrogen bonds between bases → stable / strong molecule ● Double helix with sugar phosphate backbone → protects bases / hydrogen bonds ● Long molecule → store lots of genetic information (that codes for polypeptides) ● Double helix (coiled) → compact

Question 62

Why is semi-conservative replication important?

Answer 62

ensures genetic continuity between generations of cells.

Question 63

Describe the process of semi-conservative DNA replication

Answer 63

1. DNA helicase breaks hydrogen bonds between complementary bases, unwinding the double helix 2. Both strands act as templates 3. Free DNA nucleotides attracted to exposed bases and join by specific complementary base pairing 4. Hydrogen bonds form between adenine-thymine and guanine-cytosine 5. DNA polymerase joins adjacent nucleotides on new strand by condensation reactions 6. Forming phosphodiester bonds

Question 64

Use your knowledge of enzyme action to suggest why DNA polymerase moves in opposite directions along DNA strands

Answer 64

● DNA has antiparallel strands ● So shapes / arrangements of nucleotides on two ends are different ● DNA polymerase is an enzyme with a specific shaped active site ● So can only bind to substrate with complementary shape (phosphate end of developing strand)

Question 65

Describe the work of Meselson and Stahl in validating the Watson-Crick model of semi-conservative DNA replication

Answer 65

1. Bacteria grown in medium containing heavy nitrogen (15N) and nitrogen is incorporated into DNA bases ● DNA extracted & centrifuged → settles near bottom, as all DNA molecules contain 2 ‘heavy’ strands 2. Bacteria transferred to medium containing light nitrogen (14N) and allowed to divide once ● DNA extracted & centrifuged → settles in middle, as all DNA molecules contain 1 original ‘heavy’ and 1 new ‘light’ strand 3. Bacteria in light nitrogen (14N) allowed to divide again ● DNA extracted & centrifuged → half settles in middle, as contains 1 original ‘heavy’ and 1 new ‘light’ strand; half settles near top, as contains 2 ‘light’ strands

Question 66

Describe the structure of ATP

Answer 66

● Ribose bound to a molecule of adenine (base) and 3 phosphate groups ● Nucleotide derivative (modified nucleotide)

Question 67

Describe how ATP is broken down

Answer 67

● ATP (+ water) → ADP (adenosine diphosphate) + Pi (inorganic phosphate) ● Hydrolysis reaction, using a water molecule ● Catalysed by ATP hydrolase (enzyme)

Question 68

Give two ways in which the hydrolysis of ATP is used in cells

Answer 68

● Coupled to energy requiring reactions within cells (releases / provides energy) ○ Eg. active transport, protein synthesis ● Inorganic phosphate released can be used to phosphorylate (add phosphate to) other compounds, making them more reactive

Question 69

describe how ATP is resynthesised in cells

Answer 69

● ADP + Pi → ATP (+ water) ● Condensation reaction, removing a water molecule ● Catalysed by ATP synthase (enzyme) ● During respiration and photosynthesis

Question 70

Suggest how the properties of ATP make it a suitable immediate source of energy for cells

Answer 70

● Releases energy in (relatively) small amounts / little energy lost as heat ● Single reaction / one bond hydrolysed to release energy (so immediate release) ● Cannot pass out of cell

Question 71

Explain how hydrogen bonds occur between water molecules

Answer 71

● Water is polar molecule ● Slightly negatively charged oxygen atoms attract slightly positively charged hydrogen atoms of other water molecules

Question 72

Explain 5 properties of water that are important in biology

Answer 72

-Metabolite-Used in condensation / hydrolysis / photosynthesis / respiration -Solvent (can dissolve solutes)-1. Allows metabolic reactions to occur (faster in solution) and allows transport of substances eg. nitrates in xylem, urea in blood -High specific heat capacity- ● Buffers changes in temperature ● As can gain / lose a lot of heat / energy without changing temperature 1. Good habitat for aquatic organisms as temperature more stable than land 2. Helps organisms maintain a constant internal body temperature -High latent heat of vaporisation- ● Allows effective cooling via evaporation of a small volume (eg. sweat) ● So helps organisms maintain a constant internal body temperature -Strong cohesion between water molecules-1. Supports columns of water eg. transpiration stream through xylem in plants and produces surface tension, supporting small organisms (to walk on water)

Question 73

Describe the role of hydrogen ions.

Answer 73

● Maintain pH levels in the body → high conc. = acidic / low pH ● Affects enzyme rate of reaction as can cause enzymes to denature (topic 1.4.2)

Question 74

Describe the role of iron ions.

Answer 74

● Component of haem group of haemoglobin ● Allowing oxygen to bind / associate for transport as oxyhaemoglobin (topic 3.4.1)

Question 75

Describe the role of sodium ions.

Answer 75

1. Involved in co-transport of glucose / amino acids into cells (topic 2.3 / 3.3) 2. Involved in action potentials in neurons (topic 6.2) 3. Affects water potential of cells / osmosis (topic 2.3)

Question 76

Describe the role of phosphate ions.

Answer 76

1. Component of nucleotides, allowing phosphodiester bonds to form in DNA / RNA 2. Component of ATP, allowing energy release 3. Phosphorylates other compounds making them more reactive (topic 1.6) 4. Hydrophilic part of phospholipids, allowing a bilayer to form (topic 1.3 / 2.3)