Genetic information, variation and relationships between organisms

  • Created by: Eloise
  • Created on: 17-06-20 11:45


Genomics:study of a whole set of genetic information in the form of DNA base sequences that occurs in the cells of organisms of a particular species.

Genome: is the complete set of genetic information within an organism/cell.

Genetic code: is universal because the same specific base triplet codes for the same amino acids in all living things.

Non-coding DNA: fills the gaps between genes, not junk, carries out regulatory functions.

Introns: don't code for amino acids, found in eukaryotic cells, removed during protein synthesis.

Exons: genes that code for amino acids.

Non-overlapping: each base is part of one codon, it is not part of the one before or after.

Gene: a sequence of bases that code for polypeptides/functional RNA.

Amino acid: 3 bases (triplet), also called a codon.

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Storing DNA

Eukaryotic cells:

- Contains linear DNA molecules (chromosomes).

- Really long.

- Wound around histone proteins that support DNA.

Prokaryotic cells:

- Shorter and circular.

- Condenses by supercoiling.

- Mitochondria have small amounts of their own DNA.

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Eukaryotic chromosome structure

- Located in the nucleus.

- Formed from the coiling of chromatin.

- Wrapped around histone proteins - forms protein-DNA complex called chromatin.

- Takes up less space.

- Genes can only be expressed when the DNA is unwound.

- DNA has a double helix strucutre.

- Made up of many building blocks called nucleotides joined together. 

- Most common genes will be expressed on the outside so they are more accessible.

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- Made by transcription in the nucleus.

- Acts as template for translation in cytoplasm.

- Sequences of bases determines sequence of amino acids.

- Straigh chain molecule.

- Chemically unstable - breaks down after a few days.

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- Carries an amino acid at the binding site.

- Anticodon is complementary to mRNA codon.

- Specific to one amino acid.

- Single polynucleotide strand.

- Folded in three-leafed clover shape.

- Held together by hydrogen bonds.

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- In the nucleus.

- DNA unzipped/unwound by helicase - hydrogen bonds broken.

- RNA nucleotides align next to their complementary bases on template strand.

- Form temporary hydrogen bonds (U replaces T).

- RNA polymerase joins adjacent nucleotides - condensation reaction.

- Forms phosphodiester bonds.

- RNA polymerase reaches stop codon.

- mRNA leaves nucleus via nuclear pore.

- Hydrogen bonds reform and DNA winds back up again.

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Post transcriptional modification

- Eukaryotic cells contain introns and exons - might be evolutionary.

- The whole gene is transcribed to pre-mRNA.

- Splicing removes introns and splices exons together.

- Prokaryotic cells don't contain introns so mRNA is produced directly from DNA.

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- Every single protein starts with methionine (universal start codon, essential amino acid).

1. mRNA attaches itself to a ribosome.

2. tRNA molecule carry amino acids to the mRNA.

3. tRNA molecule with anticodons complementary to first codon on mRNA attaches itself.

4. Second tRNA molecules attahces to the next codon.

5. Two amino acids join by peptide bond and first tRNA molecule moves away.

6. Another tRNA molecule comes along and attaches to the next codon on mRNA, it's amino acid joins via peptide bond.

7. Process continues producing polypeptide chain until stop codon is reached.

8. Polypeptide chain moves away from ribosome.

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Roles of ATP, tRNA and ribosomes in translation.


- Hydrolysis of ATP releases energy.

- To help form the bonnd between adjacent amino acids and amino acids + tRNA molecule.


- Transport specific amino acids.

- Help bring two amino acids together to form peptide bonds.

- About 60 types of tRNA to carry 20 amino acids - genetic code is degenerate.


- Attaches to mRNA, houses tRNA, allows complementary base pairings.

- Allow peptide bonds to form between amino acids.

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- Change in the base sequence of DNA on chromosomes.

- Can arise spontaneously during DNA replication (interphase).

- Involves base deletion/substitution.

1. Change in base/triplet sequence of DNA/gene.

2. Change in sequence of codons.

3. Change in sequence of amino acids in primary structure.

4. Change in position of hydrogen/ionic/covalent bonds in tertiary structure.

5. Change in shape of active site.

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Base deletion and substitution

Base deletion

- One nucleotide removed from DNA sequence.

Base substitution

- Nucleotide replaced with another nucleotide.

1. Changes one mRNA codon and one amino acid.

2. Sequence of amino acids in primary structure of polypeptide changes.


3. Due to degenerate nature of genetic code, new triplet may still code for the same amino acid so sequence of amino acids is the same.

4. Polypeptide remains unchanged.

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Transcription in prokaryotes

- Occurs in the cytoplasm.

- Allows mRNA molecules to be longer.

- mRNA less modified, no need to protect it.

- Translation happens almost immediately.

- Lifespan of prokaryotic mRNA = 2 minutes (eukaryotic = 10 minutes).

Operons: system by which genes are organised into groups.

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Chromosomal mutations

Point mutation

- Change in individual gene due to miscopying of one or more nucleotides.

- Deletion or insertion of nucleotide results in frameshift.

Chromosomal mutation

- Deletion, duplication, inversion and translocation.

Whole-chromosome mutation

- Entire chromosome lost or repeated during cell division.

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Effects and causes of mutations


- Mutagens

- X-rays

- Ionising radiation

- Chemicals


- Production of new/superior protein (gain reproductive advantage).

- Neutral mutation (no change).

- Production of inferior or no protein (fatal and/or disease causing). 

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