Classification and heredity – Learning Objectives
1. Discuss the diversity of organisms
2. Define the term species
3. Distinguish between inherited and acquired
variation
4. Give examples of inherited and acquired
variations
5. Define the term heredity
6. Define the term gene
7. Outline the role of a gene
8. Define the term gene expression
9. Know the structure of a chromosome
Classification and heredity – Notes
Classification = placing organisms into similar groups
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Taxonomy = science of classifying organisms
Organisms classified according to similarities in structure, function and
development.
Similarities arise from common ancestors by evolution.
Basic unit of classification is species.
Species = group of organisms capable of interbreeding naturally to produce
fertile offspring
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Variations within species may be acquired or inherited
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Acquired variations = not inherited and not genetically controlled. Eg. Ability
to walk, speak a language, ride a bicycle
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Inherited variations = inherited and genetically controlled. Eg. Eye colour,
number of fingers, the production of nails
Heredity (genetic inheritance) = passing on of features from parent to offspring
by means of genes
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 Characteristics are traits or features that are inherited genetically.
Gene = section of DNA that causes the production of a protein (units of heredity)
Gene
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expression
way in which a gene works to produce a protein.
produces the characteristics or traits that are inherited.
characteristics arise from the interaction between the inherited genes and
the environment.
Chromosomes
 60% protein and 40% DNA
 Genes arranged along a
chromosomes
 97% non-coding DNA (junk DNA)
 Coding DNA in genes are called
exons
 Non coding DNA within genes is called introns
DNA structure, replication and profiling – Learning Objectives
1. Outline the complex structure of DNA double helix
2. Name the four bases and the base pairs in DNA
3. Discuss the bonding in the DNA molecule
4. Distinguish between coding and non-coding structures
5. Define triplet base code
6. Discuss the replication of DNA
7. Discuss the stages involved in DNA profiling
8. Define the process of DNA profiling
9. Give two uses of DNA profiling
10. Define and give the use genetic screening
11. Outline the structure of RNA
12. Name the bases in RNA
Practical Activity: To isolate DNA from a plant tissue
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DNA structure, replication and profiling – notes
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James Watson and Francis Crick in 1953 discovered the structure of DNA
Structure is made up of units called nucleotides arranged in chains called
polynucleotides
Nucleotide = phosphate, a sugar and a nitrogen-containing base
Sugar = deoxyribose (DNA) or ribose (RNA)
Phosphate = PO4 (P)
Four nitrogenous bases
 Two purines (double-ring molecule) = adenine (A) and guanine (G) (the
Angel Gabriel is pure)
 Two pyrimidines (single-ringed molecule) = thymine (T) and cytosine (C)
 Adenine and thymine bond using two hydrogen bonds
 Guanine and cytocine bond using three hydrogen bonds
A = T
C = G
(At The Giants Causeway)
The polynucleotides form two helical chains
(double helix)
The genetic code
 Genes are made of DNA
 A gene is a section of DNA required for the
production of a protein
 Protein are made of combinations of amino
acids
 20 different types of amino acids combine
to form many proteins
 A Triplets (codons) are three bases in DNA
/RNA that act to code for a particular amino
acid
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Replication of DNA (makes copies of itself)
 Double helix unwinds
 Enzyme breaks the bonds between bases
 DNA enter from cytoplasm attach to exposed bases
 Each new strand (half old DNA + half new DNA/ identical) rewinds to form
double helix
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Allows for the same DNA to be passed on to each new generation of cells
(mitosis)
DNA Profiling = method of making a unique pattern of bands from the DNA of a
person
Four steps:
1. DNA is released from cells (amplified by PCR – polymerase chain reaction)
2. DNA is cut into fragments of different lengths (restriction enzymes)
3. DNA fragments are separated according to their sizes (gel electrophoresis)
4. Patterns produced are compared and analysed
Applications of DNA profiles (DNA fingerprints)
 Establish whether biological tissue at a crime scene matches a suspect
 Determine whether a person is or is not the parent of a child
Genetic screening = a person’s DNA can be tested to show the presence of
abnormal or altered genes (which may cause disease)
RNA (ribonucleic acid)
 Differences between DNA and RNA
DNA
RNA
Deoxyribose
Ribose
Thymine (T)
Uracil (U)
Double-stranded (double helix)
Single-stranded
Found in nucleus
Found in the nucleus and cytoplasm
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To isolate DNA from onion cells:
1. cut up onion tissue. Put in a salt/detergent mixture (to clump DNA and break
down cell membranes)
2. put in a water bath at 60°C (denatures enzymes that digest DNA)
3. cool mixture in ice water bath (slows DNA breakdown)
4. blend for 3 seconds (breaks cell walls and releases DNA)
5. filter the mixture (to remove cell parts);
proteins and DNA form the filtrate
6. add protease enzyme to the filtrate (to
remove the protein)
7. add ice-cold ethanol (to precipitate the
insoluble DNA)
8. gently twist a glass rod to remove DNA
(clear mesh)
Protein Synthesis - Learning Objectives
1.
Outline the steps in protein synthesis
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Understand DNA contains the code for protein
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Understand this code is transcribed to mRNA
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Know the code is translated on the ribosome
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Understand the amino acids are assembled in the correct order to
synthesise the protein
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Know that the protein folds into its functional shape
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Know that genes control cell activities by producing proteins
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Understand that enzymes unwind the DNA
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Know the role of RNA polymerase
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Know what a codon is
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Know the ribosome is composed of subunits
12.
Understand the amino acids are assembled in the correct order
determined by the codons on mRNA to synthesise the protein
13.
Understand a stop codon on mRNA signals the release of the protein
14.
Know that the protein folds into its functional shape
15.
Understand the molecular involvement of DNA, mRNA, tRNA, rRNA and
amino acids in the process of protein synthesis
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Protein Synthesis – Notes
Initiation: enzymes open up the DNA double helix at the site of a gene that is going
to produce the protein
Transcription: the DNA code is transcribed onto a complementary mRNA strand
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Translation: The production of a protein according to RNA code
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mRNA strand leaves the nucleus and enters a ribosome (rRNA) in the
cytoplasm
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every tRNA has a complementary triplet to the triplets on the mRNA
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tRNA molecules enter the ribosome
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each tRNA has a specific amino acid (eg. Valine)
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the amino acids are attached to each other at the ribosome to form a protein
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the protein folds into shape
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