Biology by Bradford
A1.2.1The genetic material
The genetic material of every living organism is . Some use RNA instead, but they are not counted as living organisms.
A1.2 Nucleic acids: revision map
The subtopic in the middle and eleven tasks round it: label five diagrams, complete three tables, put a process in order and fill 51 gaps. Every standard level statement has a box; the five boxes for higher level only are dashed and badged HL, and drop off for an SL class. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
Nucleic acids
Molecules · Unity and diversityHover over a box to see it. Untick it to leave it off this sheet and its printout.
NameA1.2.2, A1.2.3, A1.2.5A nucleotide
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Nucleotides join by reactions into a chain, each linked to the next by bonds: a strong backbone with the bases sticking out from it. RNA is one such chain.
A1.2.14Hershey and ChaseHL
Number the steps in order.
- Spin it in a centrifuge: the bacteria form a pellet, the coats stay in the liquid.
- ³²P is in the pellet, ³⁵S in the liquid: DNA, not protein, entered the bacteria.
- Label one batch of viruses' protein coats with ³⁵S and another batch's DNA with ³²P.
- Shake the mixture in a blender to knock the virus coats off the bacteria.
- Let each batch infect bacteria.
So the genetic material is .
A1.2.15Chargaff's dataHL
| Source | % A | % T | % G | % C |
|---|---|---|---|---|
| Human | 31 | 29 | 20 | 20 |
| Wheat | 27 | 27 | 23 | 23 |
| Yeast | 31 | 33 | 19 | 17 |
| E. coli | 25 | 24 | 26 | 26 |
In every species %A is close to % and %G close to %, so purines equal : evidence for complementary base pairing.
A1.2.7DNA and RNA
| DNA | RNA | |
|---|---|---|
| Pentose sugar | ||
| Bases | A, , C, G | A, , C, G |
| Number of strands | ||
| Shape | a single strand |
A1.2.13A nucleosomeHL
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DNA wraps about twice round a core of histone proteins, packing it into the nucleus and helping control which genes are expressed.
A1.2Nucleic acids
A1.2 examA model of a nucleotide made from three joined shapes
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A1.2.4, A1.2.6The double helix
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The two strands run in opposite directions: they are . Adenine pairs with and cytosine with , held by hydrogen bonds.
A1.2.8, A1.2.9, A1.2.10Copying and reading the code
Each base pairs with only one other, so either strand can act as a : complementary base pairing lets DNA be and its information . A stretch n bases long can be arranged in to the power n ways, so the storage capacity of DNA is almost limitless. Every living thing uses the same genetic code: evidence of .
A1.2.11Which end is which?HL
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New nucleotides are added to the end, so nucleic acids are built in the 5′ to 3′ direction.
A1.2.12Purines and pyrimidinesHL
| Base | Purine or pyrimidine? | Rings |
|---|---|---|
| Adenine | ||
| Guanine | ||
| Cytosine | ||
| Thymine |
A purine always pairs with a , so the helix keeps the same width all along.
Word bank 3′3′ end45′ endantiparallelCcondensationcovalentdeoxyriboseDNAdouble helixeightexpressedguanineH1 histonehistoneshydrogen bondnitrogenous baseonepentose sugarphosphatepurinepyrimidinepyrimidinesreplicatedribosesugar-phosphatesugar-phosphate backboneTtemplatethyminetwoUuniversal common ancestryviruses
Answer key
Every box on the sheet with its gaps filled in, as the subtopic reads in full.
GapsThe genetic material
The genetic material of every living organism is DNA. Some viruses use RNA instead, but they are not counted as living organisms.
LabelA nucleotide
- phosphate
- pentose sugar
- nitrogenous base
Nucleotides join by condensation reactions into a chain, each linked to the next by covalent bonds: a strong sugar-phosphate backbone with the bases sticking out from it. RNA is one such chain.
TableDNA and RNA
DNA RNA Pentose sugar deoxyribose ribose Bases A, T, C, G A, U, C, G Number of strands two one Shape double helix a single strand LabelThe double helix
- hydrogen bond
- nitrogenous base
- sugar-phosphate backbone
The two strands run in opposite directions: they are antiparallel. Adenine pairs with thymine and cytosine with guanine, held by hydrogen bonds.
GapsCopying and reading the code
Each base pairs with only one other, so either strand can act as a template: complementary base pairing lets DNA be replicated and its information expressed. A stretch n bases long can be arranged in 4 to the power n ways, so the storage capacity of DNA is almost limitless. Every living thing uses the same genetic code: evidence of universal common ancestry.
LabelWhich end is which? HL
- 5′ end
- 3′ end
- 3′ end
- 5′ end
New nucleotides are added to the 3′ end, so nucleic acids are built in the 5′ to 3′ direction.
TablePurines and pyrimidines HL
Base Purine or pyrimidine? Rings Adenine purine two Guanine purine two Cytosine pyrimidine one Thymine pyrimidine one A purine always pairs with a pyrimidine, so the helix keeps the same width all along.
LabelA nucleosome HL
- histones
- DNA
- H1 histone
DNA wraps about twice round a core of eight histone proteins, packing it into the nucleus and helping control which genes are expressed.
OrderHershey and Chase HL
- Label one batch of viruses' protein coats with ³⁵S and another batch's DNA with ³²P.
- Let each batch infect bacteria.
- Shake the mixture in a blender to knock the virus coats off the bacteria.
- Spin it in a centrifuge: the bacteria form a pellet, the coats stay in the liquid.
- ³²P is in the pellet, ³⁵S in the liquid: DNA, not protein, entered the bacteria.
So the genetic material is DNA.
TableChargaff's data HL
Source % A % T % G % C Human 31 29 20 20 Wheat 27 27 23 23 Yeast 31 33 19 17 E. coli 25 24 26 26 In every species %A is close to %T and %G close to %C, so purines equal pyrimidines: evidence for complementary base pairing.
Exam diagramA model of a nucleotide made from three joined shapes
- phosphate
- pentose sugar
- nitrogenous base