chapter 3 - biological molecules Flashcards
(79 cards)
1
Q
elements found in water
A
H and O
2
Q
elements found in carbohydrates
A
C, H and O: usually in the ratio Cx(H20)x
3
Q
elements found in lipids
A
C, H and O
4
Q
elements found in proteins
A
C, H, O, N and S
5
Q
elements found in nucleic acids ie DNA
A
C, H, O, N and P
6
Q
polymers
A
long-chain molecules made up of repeating units called monomers
7
Q
condensation reaction
A
removal of water to join molecules
8
Q
hydrolysis reaction
A
water is used to split a molecule
9
Q
inorganic ions
A
atoms or molecules that have an uneven charge (through the loss or gain of electrons)
10
Q
cations
A
ions where electrons have been lost giving a positive (+ve) charge
11
Q
anions
A
ions where electrons have been gained giving a negative (-ve) charge
12
Q
electrolytes
A
inorganic ions dissolved in water
13
Q
roles of electrolytes
A
controls:
- osmosis
- nerve impulses
- muscle contraction
- activating enzymes
- pH
14
Q
explain how water is a polar molecule
A
oxygen nucleus has more protons and therefore more positive charge than hydrogen nucleus; attracts the negative electrons more; electrons spend more time closer to oxygen; more electrons near oxygen gives it a slightly negative charge; lack of electrons near hydrogen gives it a slightly positive charge
15
Q
properties of water (LILACSS)
A
- liquid
- ice is less dense than water
- (high) latent heat of vaporisation
- adhesion
- cohesion
- solvent
- (high) specific heat capacity
16
Q
carbohydrates
A
- hydrated carbon
- contains C, H and O
- general formula (CH2O)n
17
Q
functions of carbohydrates
A
- source of energy eg glucose
- store of energy eg starch, glycogen
- structural units eg cellulose and chitin
- components of nucleic acids and glycolipids
18
Q
properties of monosaccharides
A
- sweet
- soluble in water
- form crystals
19
Q
disaccharides
A
two monosaccharides join to form a disaccharide
20
Q
properties of disaccharides
A
- sweet
- soluble in water
- form crystals
21
Q
(alpha) glucose + (alpha) glucose ->
A
maltose
22
Q
(alpha) glucose + fructose ->
A
sucrose
23
Q
(alpha) glucose + galactose ->
A
lactose
24
Q
polysaccharides
A
polymers that are made of repeating monosaccharides that have undergone condensation reactions to join together
25
properties of polysaccharides
- not sweet
- insoluble in water
- cannot be crystalised
26
starch
polysaccharide of amylose and amylopectin which are polysaccharides of alpha glucose
27
amylose
formed when (alpha) glucose molecules are joined by 1-4 glycosidic bonds and form a coiled structure; hydroxyl groups of carbon 2 are inside the coil making the molecules less soluble and hydrogen bonds maintain the coiled structure
28
amylopectin
formed when (alpha) glucose molecules are joined by 1-4 glycosidic bonds and form a coiled structure. there are also some branches formed by 1-6 glycosidic bonds
29
glycogen
polysaccharide of alpha glucose joined by 1-4 and some 1-6 glycosidic bonds
30
1-4 glycosidic bonds
a type of covalent bond formed in condensation reactions of monosaccharides between carbon 1 and carbon 4 on the molecules
31
cellulose
polysaccharide of beta glucose joined by 1-4 glycosidic bonds with hydrogen bonds between layers
32
formation of cellulose
to form the glycosidic bonds, alternate beta glucose molecules are rotated through 180 degrees (3d) forming straight chains. the straight chains have lots of hydroxyl groups projecting from carbon 2 which form hydrogen bonds with adjacent cellulose molecules
33
lipids
macromolecules that contain large amounts of carbon and hydrogen atoms with fewer oxygen atoms - they are soluble in organic solvents only (ie alcohol)
34
functions of lipids
- energy store
- thermal insulation
- protection/cushioning
- buoyancy
35
structure of glycerol
alcohol with 3 carbons and 3 OH groups
36
structure of fatty acids
has:
- carboxyl group COOH
- hydrocarbon tail; carbon and hydrogen varies in length and structure (2-20 carbons long)
are hydrophobic making lipids insoluble in water
37
saturated fatty acids
there are no double bonds between carbon atoms
38
unsaturated fatty acids
there is at least one double bond between carbon atoms. this causes the chain to kink
39
monounsaturated
there is just one double bond
40
polyunsaturated
there are double bonds
41
synthesis and breakdown of triglycerides
- a condensation reaction occurs between the COOH group of the fatty acid and the OH group of the glycerol
- the bond formed is an ester bond
- the reaction can be termed esterification
- ester bonds can be broken by hydrolysis reactions
42
triglyceride functions
mainly used as a compact energy store as they contain a high proportion of C-H bonds and therefore release about twice as much energy per gram compared to carbohydrates
43
test for starch
1. add a couple of drops of iodine solution to test the sample
2. if starch is present, the sample will change to a blue-black colour
3. if there's no starch, the iodine solution will stay brown
44
test for reducing sugars
1. to test the sample, add an equal volume of Benedict's solution
2. heat in a water bath
3. a brick-red precipitate forms
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test for non-reducing sugars
1. add hydrochloric acid to the test solution and boil in water bath
2. cool the tube and neutralise the acid by adding alkali then test with universal indicator
3. repeat the Benedict's test again. if sucrose was present it will have hydrolysed to glucose and fructose and give a positive result
46
functions of phospholipids
form a key role in cell membranes, are selectively permeable
47
cholesterol
a sterol: a lipid not made from fatty acids and glycerol
48
functions of cholesterol
regulates fluidity and manufactures vitamin D and steroid hormones
49
emulsion test for lipids
1. crush material and mix well with ethanol
2. decant or filter the suspension to remove any solid particles
3. carefully pour the ethanol solution onto some water in a calean test tube - don't mix them
positive result - a milky white emulsion forms on the top of the water
negative result - solution remains clear
50
peptide bond
covalent bonds that form between amino acids (formed between C and N)
51
testing for proteins - biuret test
1. mix 1cm3 of suspention or solution with an equal volume of biuret solution
2. swirl the tube and look for a colour change (from blue to lilac)
3. the chemicals in the biuret solution react with the peptide bonds in a protein
52
primary structure of proteins
the specific sequence of amino acids which is determined by the genetic code (DNA)
53
secondary structure
how a polypeptide folds, it forms one of two structures: α-helix and β-pleated sheet and are stabilised by hydrogen bonds
54
tertiary structure
the way the secondary structure folds and is held together by disulfide bonds, ionic bonds, hydrogen bonds and hydrophobic/hydrophilic interactions
55
quanternary structure
if a protein is made of two or more polypeptide chains then it has a quanternary strucutre which is the way the tertiary structures are held together. they are held together by the same bonds as the tertiary structure
56
globular proteins (structure, solubility, role)
3D feature - roll up to form balls
primary structure - very precise, usually a non-repeating amino acid sequence
secondary and tertiary structure - complex
solubility in water - usually soluble
role - usually metabolic; enzymes, hormones, transport
57
fibrous proteins (structure, solubility, role)
3D structure - form long, narrow fibres
primary structure - often long molecules with simple, repeating amino acid sequence
secondary and tertiary structure - simple
solubility in water - usually insoluble
role - usually structural
58
examples of globular proteins
haemoglobin, insulin, pepsin
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examples of fibrous proteins
collagen, keratin, elastin
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conjugated proteins
proteins that contain a non-protein part, eg haem groups in haemoglobin
61
nucleic acids
polymers made of monomer units called nucleotides
examples: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)
62
structure of nucleotides
includes a phosphate group, pentose sugar and a nitrogenous base
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nitrogenous bases
adenine, thymine, cytosine and guanine
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phosphorylated nucleotides
contain more than one phosphate group eg adenosine triphosphate (ATP)
65
formation of DNA
nucleotides join up between the phosphate group on one nucleotide and the carbon 3 of the sugar of another via a condensation reaction; this forms a phosphodiester bond
DNA consists of two polynucleotide strands that are made of a sugar-phosphate backbone attatched to nitrogenous bases forming a twisted double helix
66
the bases of DNA are complementary so the pairings are always:
A-T (ademine to thymine) forming 2 hydrogen bonds
C-G (cytosine to guanine) forming 3 hydrogen bonds
67
DNA in eukaryotes
the majority of DNA is in the nucleus
DNA is wound around histone proteins, making chromosomes
there are also loops of DNA without histones inside mitochondria and chloroplasts
68
DNA in prokaryotes
DNA is a loop within the cytoplasm -
no nulceus it is 'naked' -
not wound around histone proteins small loops called plasmids often present
69
when does DNA replication take place?
interphase
70
stages of DNA replication
1. DNA untwists and unzips by DNA helicase
2. free nucleotides bind at the exposed complementary bases
3. hydrolysis releases the extra phosphate groups from nucleotides and supplies the energy to form the phosphodiester bonds between the sugar of one nucleotide and the phosphate of the adjacent nucleotide which is catalysed by DNA polymerase
71
leading strand
synthesised continuously by DNA polymerase
72
lagging strand
synthesised in fragments (Okazaki fragments) by DNA ligase ("top" strand)
73
triplet
a sequence of 3 bases
74
gene
a sequence of nucleotide bases that codes for a whole protein
75
protein synthesis
- DNA is found in chromosomes and cannot pass our through the nuclear pores
- a copy of each gene has to be transcribed into a length of mRNA (messenger ribonucleic acid)
- this can pass out of the nucleus and moves to a ribosome where it is translated to make a protein
76
differences of RNA and DNA
- RNA has a ribose sugar; DNA has a deoxyribose sugar
- RNA is single stranded; DNA is double stranded
- uracil in RNA replaced thymine in DNA
77
main forms of RNA
mRNA - transfers information to ribosome
rRNA - provides site of protein assembly
tRNA - carries amino acids to ribosomes
78
transcription
- a section of DNA (gene) unzips
- RNA nucleotides forms bases with exposed complementary bases on template strand
- RNA polymerase checks for mistakes and catalyses formation of phosphodiester bonds
- at a stop triplet, the mRNA breaks off and leaves the nucleus
79
translation
- mRNA attaches to ribosome
- tRNA has specific amino acids attached to it
- tRNA anticodon joins onto the mRNA CODON
- the process repeats and a peptide bond forms between amino acids and the ribosome moves along
- this continues down the length of the mRNA strand until it reaches a stop codon
