Cellular Control F215
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- Created on: 11-02-14 19:41
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- Cellular Control
- The Genetic Code
- Genes are lengths of DNA that code for the structure of polypeptides.
- Polypeptides may be proteins or code for part of a protein.
- The proteins include structural proteins and enzymes.
- A sequence of organic bases in DNA, the bases are read in triplets
- Each triplet codes for a specific amino acid
- The number of triplets determines the number of amino acids in the polypeptide
- Protein Synthesis
- 1st Transcription
- 1. Transcription is the conversion of the genetic code to a sequence of nucelotidesin messenger RNA (mRNA)
- 2. The DNA molecule is too large to leave the nucleus so smaller mRNA is made.
- 3. The DNA molecule is unwound and split by the action of enzyme RNA polymerase.
- 4. RNA nucleotides form a molecule complimentary to the template strand of the DNA molecule. The rules of base pairing are followed.
- 3. The DNA molecule is unwound and split by the action of enzyme RNA polymerase.
- 2. The DNA molecule is too large to leave the nucleus so smaller mRNA is made.
- 1. Transcription is the conversion of the genetic code to a sequence of nucelotidesin messenger RNA (mRNA)
- 2nd Translation
- 1. The mRNA attaches itself to a ribosome and transfer RNA (tRNA) molecules carry amino acids to the ribosome.
- 2. A tRNA molecule, with an anticodon that's complimentary to the first codon on the mRNA, attaches itself to the mRNA by complimentary base pairing.
- 3. A second tRNA molecule attaches itself to the next codon on the mRNA in the same way.
- 4. The two amino acids attached to the tRNA molecules are joined by a peptide bond. The first tRNA molecule moves away leaving the amino acid behind.
- 5. A third tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first two and the second tRNA molecule moves away.
- 6. The process continues producing a chain of linked amino acids until a stop codon is reached. The polypeptide chain then moves away.
- 5. A third tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first two and the second tRNA molecule moves away.
- 4. The two amino acids attached to the tRNA molecules are joined by a peptide bond. The first tRNA molecule moves away leaving the amino acid behind.
- 3. A second tRNA molecule attaches itself to the next codon on the mRNA in the same way.
- 2. A tRNA molecule, with an anticodon that's complimentary to the first codon on the mRNA, attaches itself to the mRNA by complimentary base pairing.
- 1. The mRNA attaches itself to a ribosome and transfer RNA (tRNA) molecules carry amino acids to the ribosome.
- 1st Transcription
- Mutations
- Any change to the base (nucleotide) sequence of the DNA is called a mutation
- Substitution - one base is swapped for another one
- Deletion - one base is removed
- Cause a frameshift
- Insertion - one base is added
- Cause a frameshift
- Insertion - one base is added
- Duplication - one or more bases are repeated
- Inversion - a sequence of bases is reversed
- Neutral Mutations
- The mutation is in a non-coding region of DNA
- Silent mutation - although the base triplet has changed, it still codes for the same amino acid
- Beneficial Mutations
- A mutation may alter a polypeptide such that it works more effectively.
- The Lac Operon
- A functional unit of genes in the genome of prokaryotic cells found in the bacterium E. coli.
- Contains two genes which code for the structure of proteins and a genetic control mechanism to enable genes to be switched on and off.
- The bacterium is not able to digest the sugar lactose, this is because it does not make the enzyme B-galactosidase. When lactose is available the gene is switched on and can produce B-glacatosidase.
- Lactose Absent
- 1. The regulator gene is expressed and the repressor protein is synthesised. It has two binding sites, one that binds to lactose and one that binds to the operator region.
- 2. The repressor protein binds to the operator region. This covers where RNA polymerase normally attaches.
- 3. RNA polymerase can't bind to the promoter region so the structural genes can't be transcribed into mRNA.
- 4. Without mRNA these genes can't be translated and the enzymes B-galactosidase and lactose permease can't be synthesised.
- 3. RNA polymerase can't bind to the promoter region so the structural genes can't be transcribed into mRNA.
- 2. The repressor protein binds to the operator region. This covers where RNA polymerase normally attaches.
- 1. The regulator gene is expressed and the repressor protein is synthesised. It has two binding sites, one that binds to lactose and one that binds to the operator region.
- Lactose Present
- 1. Lactose binds to the repressor protein.
- 2. The repressor protein can no longer bind to the operator region, but RNA polymerase can bind to the promoter region and start transcription.
- 3. Structural genes Z and Y are now expressed into the lac enzymes, B-galactosidase and lactose permease.
- 4. The E. coli bacteria can use the lactose permease enzyme to take up lactose into their cells. The lactose can then be converted to glucose and galactose using the B-galactosidase enzyme. The sugars can then be used for respiration.
- 3. Structural genes Z and Y are now expressed into the lac enzymes, B-galactosidase and lactose permease.
- 2. The repressor protein can no longer bind to the operator region, but RNA polymerase can bind to the promoter region and start transcription.
- 1. Lactose binds to the repressor protein.
- Lactose Absent
- Homeobox Sequences
- Control the body plan of an organism
- This is achieved by controlling the differentiation of cells and parts of the body through switching genes on and off at appropriate times during development.
- As homeobox genes are activated, they activate structural genes in a carefully coordinated sequence to ensure that features develop in the correct way.
- A homeobox gene contains a sequence of 180 base pairs known as a homeobox sequence.
- This sequence codes for a sequence of 60 amino acids, which is found in the polypeptide produced.
- Homeobox genes are activated in a particular order that matches the order in which they are expressed from head to tail.
- Arranged into groups called hox clusters.
- The fruit fly (Drosophila) has two clusters.
- Cluster A controls the development of the head and thorax.
- Cluster B controls development of the thorax and abdomen.
- The fruit fly (Drosophila) has two clusters.
- Arranged into groups called hox clusters.
- Homeobox genes are similar in all plants, animals and fungi, this is because they have the same role in each case.
- They code for transcription factors that need to bind to DNA.
- Control the body plan of an organism
- Apoptosis
- A series of carefully controlled biochemical events that leads to orderly cell death.
- 1. Enzymes break down the cytoskeleton
- 2. The cell shrinks, the organelles are packed together
- 3. The cell surface membrane breaks up to form vesicles, containing the cell contents.
- 4. The vesicles are taken up by phagocytes and digested
- 3. The cell surface membrane breaks up to form vesicles, containing the cell contents.
- 2. The cell shrinks, the organelles are packed together
- Important part of development
- Separates fingers and toes
- The Genetic Code
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