Summary Genetics, variation and interdependence notes

Sunday, 4 September y

Genetics, Variation & Interdependence
DNA, Genes & Chromosomes
DNA
Similar Differences Eukaryotic Prokaryotic

Nucleotide structure is Length Long Short
the same (phosphate,
deoxyribose and base)
Nucleotides joined by a Shape Linear Circular
phosphodiester bond
Contain the same 4 Proteins Associated with histones Not associated
bases - A, T, C, U
Both made of triplet Non coding regions Introns and multiple re- None
codons peats
Both helical amount of DNA many DNA one molecule
Both double stranded

Both code for the same
amino acids




Non-coding regions

- introns (within genes)
- Multiple repeats (between genes)
Introns change at a slower rate than exons

- Introns do not code for amino acids
- no selection pressure
Histones

- proteins that DNA molecules wrap around

mRNA will be the same as DNA coding strand but with U instead of T

Bases

Ratio of (C+A):(G+T) is constant but (A+T):(C+G) can vary

- purines (A and G) always pair with pyrimidines (T+C)
- A + T and C+G will always pair
- so the number of A will always be the same as the number of T

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Bonds between bases

- in a dinucleotide - phosphodiester bond between nucleotides
- hydrogen bonds between DNA strands (A + T = 2 H bonds) (C and G = 3 H bonds)
How can animals have the same percentages of bases but yet be different

- sequence of bases will be different - different codons
- different primary structure / amino acid sequence
- different bonds form in tertiary structure due to differently charged R groups
- Proteins produced by organism affect their appearance / phenotype

Why do organisms have many different mRNA molecules but only 64 different
tRNA molecules

- There are different mRNAs for every protein
- tRNA are specific to one type of amino acid (only 64 codons)
- The code is degenerate - some amino acids can be coded for by multiple codons
Genes

code for

- amino acid sequence of a polypeptide
- or a functional RNA
Genetic code features

Universal

- same bases used and same codons code for the same amino acids in all organisms
Degenerate

- there is more than one codon that will code for an amino acid
- 64 codons for 20 amino acids
- start codon always Met - only one codon
Non-overlapping

- the sequence is read so that each base is only part of one codon
Triplets

- 3 bases are needed to code for one amino acid

Mutations


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Enzyme mutations

- will only effect the enzyme function if the mutation occurs in the area of the primary
structure that makes up the active site

Silent mutation

- substitution for a base that forms a codon that will code for the same amino acid - de-
generate genetic code
- Or substitution for a amino acid with a similar charged R group
- so the same bonds formed between R groups in the tertiary structure
Chromosomes

Homologous chromosomes

- pairs of chromosomes
Telomeres

- At the end of chromosomes
- to protect DNA from damage
Fungi

- they are eukaryotic so they are made of DNA and histones
Eukaryotic Prokaryotic

Size Larger Smaller
Shape Linear Circular
Structure Complex - DNA, some RNA, his- Simple composition - DNA and
tones some RNA
Non coding regions Non coding regions - introns and None
multiple repeats
Mitochondrial and chloroplast
chromosomes have similar struc-
tures to prokaryotic




DNA & Protein Synthesis
Genome = complete set of genes in an organism

Proteome = full set of proteins a cell can produce

All cells with a nucleus have the same genome - expression of proteome varies between
tissue

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