Topic 1.1-4 Biological molecules Flashcards
(97 cards)
1
Q
What is a saccharide?
A
Sugar units which make up carbohydrates
2
Q
How many units in a monosaccharide?
A
One
3
Q
How many units in a disaccharide?
A
Two
4
Q
How many units in a poly saccharide?
A
More than two
5
Q
Give three examples of a monosaccharide?
A
- α-glucose
- β-glucose
- ribose
6
Q
What is a hexose suger?
A
A sugar with six carbons - they have a ring structure
7
Q
What is a pentose sugar?
A
A sugar with five carbons - it has a ring structure
8
Q
How do you remember the different arrangement of OH groups in α and β glucose
A
α = down, down, up ,down
β = up, down, up, down
Refering to the OH group, H is opposite
9
Q
Explain how to remember the structure of ribose
A
Similar to glucose, but one less carbon.
OH groups all go down
10
Q
How are disaccharides made from monosaccharides?
A
Monosaccharides join by losing water in a condensation reaction
11
Q
Which carbons in α-glucose form a glycosidic bond, whats the bond called?
A
The α-glucoses are joined at carbons 1 and 4 to produce an α-1,4 glycosidic bond
12
Q
How are disaccharides separated to produce two monosaccharides?
A
Disaccharides are split by adding water in a hydrolysis reaction to break the glycosidic bond
13
Q
Give three examples of disaccharides
A
- Maltose
- Sucrose
- Lactose
14
Q
What two monosaccharides bond to form maltose?
A
Two α-glucose
15
Q
What two monosaccharides bond to form sucrose?
A
Glucose and fructose
16
Q
What two monosaccharides bond to form lactose, what type of bond is formed?
A
β-glucose and galactose joined with a β-1,4 glycosidic bond
17
Q
Describe the structure of polysaccharides
A
Polysaccharides have many sugar units. They can be unbranched, as i amylose, or branched, as in amylopectin and gylcogen.
18
Q
What is starch?
A
Starch is a mixture of amylopectin and amylose. It is used as a important energy store in plants.
19
Q
What is glycogen?
A
The carbohydrate energy store found in animals
20
Q
Give examples of α-glucose polymers
A
- Starch and glycogen
21
Q
Describe the structure of amylose and how it releates to its function?
A
Amylose has α-1,4 glycosidic bonds, this means its a straight chain. Due to hydrogen bonding the chain coils.
This makes it a compact store of glucose and therefore energy.
22
Q
Describe the structure of amylopectin and how it relates to its function
A
Amylopectin branches due to 1,6 glycosidic bonds, therefore there is less coiling.
Despite being able to store energy as densely as amylose, it has more points at which it can be broken down by enzymes, therefore energy can be released quickly
23
Q
Describe the structure of glycogen and how its related to its function
A
Gylcogen, like amylopectin has 1,6 glycosidic bonds so has branching, however this branching is more frequent than amylopectin.
This there are more points at which glycogen can be broken down, so energy can be released faster than in amylose or amylopectin, this is needed in animals.
Glycogen is less energy dense
24
Q
Describe the structure of cellulose and how its related to its function
A
β-glucose monomers join with β-1,4 glycosidic bonds, due to alternating β-glucoses being inverted. This means that hydrogen bonds can form between the OH and O atoms on another chain. This causes cellulose chains to lie flat instead of coiling. The hydrogen bonds hold the chains together to form strong microfibrils, which is needed as cellulose is used to give the plant structure.
25
What are lipids?
Lipids (fats and oils) are all hydrophobic molecules. They are all made up of fatty acids and glycerol.
26
What is a trigylceride?
Trigylcerides are lipids made of three fatty acids and a glycerol molecule.
27
How are trigylceride formed?
It is synthesised during three condensation reactions between the hydroxyl group on the glycerol and the carboxyl group on the fatty acid an ester bonds is formed between each fatty acid and the glycerol
28
In what ways may lipids vary?
* The fatty acids can be of varying lengths
* In mixed triglycerides, the fatty acids are different from each other
* Fatty acids may be saturated or unsaturated
29
What is a saturated molecule?
One that has no double bonds so is completely surrounded by hydrogens.
30
What is an unsaturated molecule?
Unsaturated molecules have double bonds between some carbons so are not completely surrounded by hydrogens.
| They have kinks
31
How does saturation affect the charecteristics of lipid?
Saturated lipids have straight chains, unsaturated lipids have a kink at each double bond. This makes cell membranes with more unsaturated lipids more fluid.
32
Give functions of lipids
* Energy storage
* Water proofing
* Insulation
* Cell membranes
33
Explain why lipids are good for water proofing
* Lipids are water repellent beacause they are hydrophobic
34
Explain why lipids are good for insulation
They are good electrical and heat insulators because water-soluble substances, like charged ions, cannot get through a polar lipid layer
35
Explain why lipids are good for energy storage
| How do they compare to carbohydrates?
Lipids are ideal as a large and long-term energy store of energy, whereas carbohydrates are better suited to short term storage. This is because per gram lipids yeild more energy than carbohydrates or protein.
Energy is released when bonds form, and more C-O bonds are made when a lipid is respired than when a carbohydrate is respired.
Lipids are also insoluble in water so travel easier in the body.
36
What is a phospholipid?
Phospholipids are closely related in structure to trigylcerides. Instead of the three fatty acids there are just two fatty acids and a phosphate group.
This means that a phospholipid has a hydrophillic head and a hydrophobic tail.
37
Explain why phospholipids are used in membranes
Due to their hydrophobic nature, in contact with water, phospholipids form a layer of film on the surface.
In living cells, where water is all around, for energetic reasons phospholipids form double layers, or bilayers, with the hydrophobic "tails"protected from the water on the inside of the layer. Biological membranes are made up of a bilayer of phospholipids.
38
How do phospholipids arranged themselves in a monolayer?
The hydrophobic tails stick up and away from the water
39
What functions do lipids serve in the cell membrane?
* Delimit the cell (the structure which determines the boundries of the cell)
* Form the main barrier to movement in and out of the cell
* Allow embedding of membrane proteins, which allows movement of molecules
* Give the membrane fluidity, allowing it to change shape. More fluid membranes contain more unsaturated fats
40
Describe the structure of an amino acid?
All amino acids share a common structure; they all have a central C atom joined to:
* A hydrogen
* An amino group
* A carboxyl group
* An R group, this vaires between amino acids (the R group effects how the amino acid bonds with other amino acids
41
Explain how a dipeptide is formed
Amino acids join by peptide bonds. This happens in a condensation, where water is lost.
The formation of a peptide bond occurs between the amino group and the carboxyl group of two amino acids. This results in a dipeptide.
42
How are poly peptides formed?
Dipeptides have a carboxyl group at one end and a amino group at the other. This means that they can join to more amino acids at either end to form a single chain. This chain is a polypeptide.
## Footnote
There are about 20 different amino acids that occur naturally, they combine in long chains so there are a vast variety of possible polypeptides
43
What is a peptide bond?
A bond between the N on an amino group and the C on a carboxyl group
| Its formed by the loss of water in a condensation reaction
44
What are the four levels of organisation of a protien?
1. Primary
2. Secondary
3. Tertiary
4. Quarternary
45
What is the primary structure of a protein?
The primary structure of a protein is the sequence of amino acids forming the polypeptide
46
How does hydrogen bonding occur between amino acids in a polypeptide chain?
Amino and carboxylic acids groups in the amino acid chain carry small amount of charge. This is negative (δ-) on the CO of the carboxylic group and positive (δ+) on the NH of the amino gorup.
These charges result in hydrogen bonds forming between parts of the chain, which stabalise the structure.
47
What is the secondary structure of a protein?
The secondary structure is where polypeptide chains are held together by many hydrogen bonds. There are two types:
* An α-helix. peptide bonds form the back bone, R groups stick out (looks like a spring)
* A β-pleated sheet. Two or more parrellel polypeptide chains form regular pleats (looks like corrgated tin roofs)
48
What is the tertiary structure of a protein?
The α-helix or β-pleated sheet structure folds further, to give unique tertiary structure.
A protein folded into its tertiary structure is held together by hydrogen bonds, ionic bonds and disulfide bonds all between R groups.
49
What is a proteins quarternary structure?
Folded chains join together to form the quarternary structure. Each folded chain is held together by hydrogen bonds, ionic bonds and disulfide bonds.
It may involve addition of a prosthetic groups.
50
What are the two main types of protein?
Fibrous and globular
51
Why is a proteins shape important?
The structure of a protein determines its properties and therefore function. This applies to all biological proteins, including enzymes, antibodies, muscle proteins, hormones, structural proteins, and transport proteins.
52
Describe the structure and functions of globular protiens
* Spherical and compact
* Hydrophillic R groups face outwars and hydrophobic R groups face inwards = usually water-soluble (form colloids in water)
* Involved in metabolic processes e.g. enzymes and haemoglobin
53
Give the structure of haemoglobin
Has four polypetide chains: two α and two β, associated with four haem prosthetic groups
54
Give the structures of haemoglobin and how they are related to it's function
Haemoglobin (Hb) is found in red blood cells. It's responsible for the binding and release of oxygen.
* Globular - can be soluble
* polypetide joined to a haem group - haem groups bind to oxygen
* Four polypeptide and haem groups - binds to four more oxygen than one haem would
55
What is co-operative binding?
| In haemoglobin
The binding of each succesive O2 to Hb alteres the tertiary structure, therefore dissociation of some O2 is harder than others, this explains the shape of oxygen dissociation curves.
56
Describe the structure and function of fibrous proteins
* Can form long chains or fibres
* Sequences of amino acids repeat
* Insoluble in water
* Useful for structure and support e.g. collagen
57
Give the structure of collagen
A fibrous protein with three polypeptide chains: two α1 and one α2
The polypeptide chains are intertwined (like rope) into a triple helix
58
Explain how the structure of collagen is related to its function
Collagen gives strength to body tissues including tendons and skin. Its structure provides this functionality:
* The three α- helices are held by are large number of hydrogen bonds and bind very tightly because every third amino acid is a glycine, which can fit into the very small space on the inside of the triple helix
* On either side of the glycines are proline and hydroxyproline, which have R groups. These maintain the strong, insoluble, fibrous structure
* Collagen molecules cross link with each other provideing further strength
| Collagen has a high tensile strength
59
Describe the structure of a nucleotide
A phosphate group is binded to a pentose sugar, the pentose sugar is bonded to a organic nitrogenous base
60
Name the pentose sugar and the bases present in DNA
The pentose sugar is deoxyribose (ribose with one less oxygen)
Adenine
Thymine
Guanine
Cytosine
61
What are the bases present in DNA
The Purine bases are adenine (A) and guanine (G)
The Pyrimidine bases are cytosine (C) and thymine (T)
62
How can you remember which are purine and which are pyrimidines
Purine: AG - Adenine, Guanine
Pyrimidines: CUT - tirangles have a sharp point so cut - Cytosine, Uracil Thymine
63
What are the base pairing rules?
Hydrogen bonds can form between amino and carbonyl groups on complementary bases.
The base pair rules are:
* A purine and always bonds with a pyrimidine base
* A always bonds with T - two H bonds
* G always bonds with C or U (RNA) - three hydrogen bonds
The hydrogen bonding hold pairs of nucelotides in seperate strands together
64
Explain why DNA structure is a double helix
In DNA:
* two poly nucleotide strands twist around each other
* One strand runs in the 3' to 5' direction, the other in the opposite direction
This results in a the double helix structure of DNA. There are 10 base pairs for each complete twist. The structure of DNA is very important for its ability to replicate and its function in protein synthesis
65
What is a phosphodiester bond, and how does it enable nucelotides to be bonded together into a polynucleotide?
Nucleotides join together to form nucleic acids through condensation reactions between thier phosphate group on C atom 5 of one nucleotide and C atom 1 of the sugar of another nucleotide. This forms a phosphodiester bond.
These bonds can link multiple nucleotides, so unlimited length chains can be formed. The repeating sugar-phosphate group links in a polynucleotide form the sugar phosphate backbone, which has:
* the bases C,G,A and T sticking out
* a hydroxyl group at one end (3') and a phosphate group at the other (5')
66
Describe the structure of nucleotides in RNA
In RNA:
* The pentose is ribose
* The purine bases are adenine (A) and guanine (G) - like in DNA
* The pyrimidine bases are cytosine (C) (as in DNA) and uracil (U)
67
Describe the structure of RNA, why is it important
RNA's structure is similar to DNA; its polynucleotides form in the same way. However, unlike DNA they are single polynucleotide strands that can:
* fold into complex shapes, held by hydrogen bonding
* remain as long thread-like molecules
The structure of RNA is important to its roles in protein synthesis. Unlike DNA, the relitively small molecules of RNA can pass out of the nucleus into the the cytoplasm to the sites of protein synthesis.
68
Describe the structure of mRNA
Messenger (m)RNA:
* Is single stranded
* Is usually not folded
* Carries codons
* Codons attach to tRNA via hydrogen bonds
69
Describe the structure of tRNA
Transfer (t)RNA:
* Is single stranded
* Is folded into a specific pattern, held together by hydrogen bonds
* Carries anticodons
* Attaches to mRNA and a specific amino acid
70
Summarise the process of semiconservative DNA replication
1. The two strands of DNA unwind and the hydrogen bonds between the bases break, allowing the DNA to be split apart or "unzip". It is catalysed by the enzyme **DNA helicase**
2. Each stand's bases act as a template. Free nucleotides pair up. The enzyme **DNA polymerase** links adjacent nucleotides and **DNA ligase** joins part-formed strands together with phosphodiester bonds
3. Two identical strands DNA molecules are formed. Each one contains one origional strand and one new strand, in other words the replication of DNA is **semiconservative**
71
Give important information about the genetic code
The genetic code is:
* Written as nucleotide bases (AGCT)
* A triplet code, a codon is formed of 3 nucleotide bases, which code for an amino acid - e.g. GGT codes for gylcine
* Non-overlapping, for example the six bases TACTTG split into only two codons, TAC and TTG not TAC,ACT,CTT and TTG
* Degenerate, there is more information than needed, most amino acids are coded for by more than one codon - e.g. Proline is coded for CCT, CCC, CCA,CCG
* It is universal, the same bases are used by all species
72
Why is it important that DNA is degenerate?
The degenerate nature of DNA means that some mutations that occur still have no effect on the protein made because the codon still codes for the same amino acid
73
What is a gene?
A gene is a sequence of bases that that codes for a sequence of amino acids in a polypeptide chain
74
What is a codon?
Each amino acid is coded for by a sequence of three bases, a codon
75
What is a start codon?
Nucleotide triplet AUG on mRNA codes for the amino acid Met and initiates translation of a poly peptide
76
What is a stop codon?
Nucleotide triplets on mRNA which don't code for an amino acid and terminate translation
77
Briefly describe the process of protein synthesis
1. Transcription - the two DNA strands are split and a new mRNA copy of DNA is produced
2. mRNA leaves the nucleus - carries the information to the ribosomes in the cytoplasm
3. Amino acids join to thier specific tRNA and are carried to the ribosomes (energy from ATP is needed to attach amino acids to tRNA
4. Translation - mRNA information is translated into a sequence of amino acids by the ribosome, the ribosome moves along the mRNA "reading" the codons, the codon of mRNA attracts the matching tRNA anticodon, the tRNA detches to go and pick up another amino acid
5. Folding and modification of completed polypeptide to produce a functional protein
78
What does transcription produce and where does it occur?
Produces mRNA
Occurs in the nucleus
79
Outline the process of transcription
1. RNA polymerase binds to the promoter region on a gene
2. Section of DNA uncoils into two strands with exposed bases. Antisense strand acts as a template
3. Free nucleotides are attracted to their complementary bases
4. RNA polymerase joins adjacent nucleotides to form phospodiester bonds
80
What happens after a strand of mRNA is transcribed?
* RNA polymerase detaches at terminator region
* Hydrogen bond reform and DNA rewinds
* Splicing removes introns from pre-mRNAin eukaryotic cells
* mRNA moves out of the nucleus via nuclear pore and attaches to ribosome
81
What is the antisense strand of DNA?
Template strand of DNA which is transcribed
82
What is the sense strand of DNA?
Strand with the same base sequence as mRNA (but with thymine instead of uracil)
83
What does translation produce and where does it occur?
Produces proteins
Occurs in cytoplasm on ribosomes
84
Outline the process of translation
1. Ribosome moves along mRNA until start codon
2. tRNA anticodon attaches to complementary bases on mRNA
3. Condensation reactions between amino acids on tRNA form petide bonds
4. Process continues to form polypeptide chain until stop codon reached
85
States the role of ATP during translation
ATP provides energy to form peptide bonds
86
What are introns?
Majority of DNA consists of non-coding regions within and between genes
87
Whats are extrons?
Regions of DNA that code for amino acids sequences. Seperated by one or more introns
88
What is a mutation?
Any change in the base sequence of DNA. Often arise spontaneously during DNA replication.
89
What is a substitution mutation?
One nucleotide in the DNA sequence is replaced by another. This is likely to be a silent mutation which doesn't change the amino acid sequence.
90
What is a deletion mutation?
A nucleotide in the DNA is lost, leading to a frame shift. Significant since entire amino acid sequence downstream of mutation will be different.
91
What is an insertion mutation?
Addition of one or more base pair to DNA sequence, often in microsatallite regions. Causes frameshift. Significant since entire amino acid sequence downstream of mutation willbe different
92
Why is DNA replication described as semiconservative?
Strands from original DNA act as templates
New DNA molecule contains 1 old strand and 1 new strand
93
Explain the role of DNA helicase in semiconservative replication
Breaks the hydrgoen bonds between base pairs to form 2 single strands, each of which can act as a template
94
How is a new strand formed during semiconservative replication?
1. Free nucleotides from nuclear sap attach to exposed base by complementary base pairing
2. **DNA polymerase** joins adjacent nucleotides on new strand in a 5' -> 3' direction via condensation reactions to form phosphodiesterbonds
3. Hydrogen bonds reform
95
Explain the role of DNA ligase
Leading strand is replicated contiuously in the same direction as replication fork. Lagging strand is replicated in Okazaki fragments in the opposite direction
DNA ligase joins gaps in fragments to form a continous strand
96
What is sickle cell amaemia?
What is its symptoms?
Genetic condition that results in abnormal haemoglobin. Impaired ability to transport oxygen = rapid heart rate, fatigue, dizziness, even death. Sickle shaped red blood cells 'stick' in vessels.
97
What causes sickle cell anaemia in humans?
Missense point mutation in the gene that codes for β- strand in haemoglobin.
On DNA: CTC (Glut) -> CAC (Val)
Change in primary structure = different tertiary structure. Abnormal haemolglobin molecules form strands that make red blood cells sickle shaped
