Protein syn

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Protein syn

  1. 1. AQA Unit 5 Biology
  2. 2. DNA RNA tRNA Shape Double stranded, twisted into a double helix and held together by hydrogen bonds. Single-stranded. Single-stranded, folded into a clover shape and held together by hydrogen bonds. Sugar Deoxyribose sugar. Ribose sugar. Ribose sugar. Bases Adenine, Guanine, Thymine, Cytosine. Adenine, Guanine, Uracil, Cytosine. Adenine, Guanine, Uracil, Cytosine. Other features • 3 adjacent bases known as a codon. • Phosphate-sugar backbone for protection. • Hydrogen bonds which can be broken for replication. • Double-helix allows for protection. • DNA is semiconservative. • DNA is the “code” for particular proteins to be present. • Three adjacent bases are a codon. • DNA is copied into RNA (transcription) and then joins with a ribosome in the cytoplasm for protein synthesis (translation). • Each tRNA molecule has a specific sequence of 3 bases called an anticodon and an amino acid binding site. • Hydrogen bonds between base pairs hold the molecule in shape. • tRNA is found in the cytoplasm where it is involved in translation by carrying amino acids used to make proteins to the ribosomes.
  3. 3. RNA polymerase attaches to DNA at the beginning of a gene. DNA (double stranded) The RNA polymerase lines up free RNA nucleotides (U replaces T) The RNA is a complimentary copy of the DNA strand. The bases are joined at the backbone, forming an mRNA molecule. mRNA moves out of the nucleus through a pore and attaches to a ribosome in the cytoplasm. The hydrogen bonds between the two DNA strands in the gene break, DNA uncoils. The RNA polymerase moves along, separating the DNA and forming the RNA. One strand is used to make a mRNA copy. The hydrogen bonds between the DNA strands reform back to a double helix. Splicing occurs to remove non-coding “introns”. The RNA polymerase reaches a “stop” signal. mRNA stops being produced and RNA polymerase detaches from DNA.
  4. 4. mRNA attaches itself to a ribosome and tRNA carry amino acids to the ribosome. tRNA with a complimentary anticodon attaches itself to the first codon on the mRNA by specific base pairing. A third tRNA molecule binds to the mRNA, its amino acid binds to the second amino acid, and the second tRNA molecule moves away. A second tRNA molecule attaches itself to the second codon on the mRNA in the same way. The amino acids which are attached to these tRNA moleculesare joined by a peptide bond. The first tRNA molecule moves, leaving its amino acid behind. The process continues in the same way, producing a chain of linked amino acids (polypeptide chain) The molecules reach a stop codon, and translation stops. The polypeptide chain moves away from the ribosome as translation is complete.
  5. 5. The code is non-overlapping, each base triplet is read in sequence and is separate to the one before it. The code is degenerate, there is more than one possible combination for most amino acids. The code is universal, the same triplets code for the same amino acids in all living things. Amino Acid DNA codon mRNA codon tRNA anticodon Serine AGA UCU AGA Leucine GAT CUA GAU Tyrosine ATA UAU AUA Valine CAC GUG CAC Alanine CGT GCA CGU Hint: The tRNA anticodon always matches the DNA triplet but with U instead of T, mRNA is always complimentary to the DNA code.
  6. 6.        Transcription factors are molecules that control the expression of genes. They are specific. In the nucleus they bind to specific DNA sites near the start of their target genes. They control expression of genes by controlling the rate of transcription. Some transcription factors, called Activators, work by increasing the rate of transcription. They help RNA polymerase join to the DNA strand. Other transcription factors, called Repressors, work by decreasing the rate of transcription. They bind to the start of the target gene, preventing RNA polymerase from binding. This stops transcription. Oestrogen can bind to a transcription factor called an oestrogen receptor, forming an oestrogen-oestrogen receptor complex. The complex can act either as an activator or a repressor, this depends on the type of cell and target gene. Small interfering RNA (siRNA) cuts up target mRNA into sections so that it can no longer be translated. This is called translation interference. Hint: “expression” just means transcription & translation!
  7. 7. Type of Mutation Effect Deletion • E.g. ATGCCT becomes ATCCT – there is a frame shift and every amino acid after the point of the deletion changes as every triplet changes. This could result in a different protein being formed, or a non-functioning enzyme. Substitution • E.g. ATGCCT becomes ATACCT – the one particular amino acid that this base belongs to can change (sometimes the substitution can still lead to the same amino acid and the same protein). The protein formed in the end could be altered. DNA mutations can be caused by errors in DNA replication OR mutagenic agents such as UV radiation, ionising radiation and some chemicals and viruses.
  8. 8. Tumour Suppressor Genes Proto-oncogenes. Tumor suppressor genes can be inactivated if a mutation occurs in the DNA sequence. The effect of a proto-oncogene can be increased if a mutation occurs in the DNA sequence. A mutated proto-oncogene is called an oncogene. When functioning normally, tumour suppressor genes slow cell division by producing proteins that stop cells dividing or cause them to self-destruct. When functioning normally, proto-oncogenes stimulate cell division by producing proteins that make cells divide. If a mutation occurs in the tumour suppressant gene, the protein isn’t produced and the cells divide uncontrollably, resulting in a tumour. If a mutation occurs, the gene can become overactive. This stimulates cells to divide uncontrollably resulting in a tumour.
  9. 9. Diagnosis Treatment Prevention Cancer – Acquired Mutations (i.e. Those due to lifestyle choices) • Normally diagnosed after symptoms have appeared. High-risk individuals can be screened for particular mutations. • Treatment is different for different mutations e.g. Some cancers are treated with drugs, others with surgery to remove chunks of the tumour, and radiotherapy. • Protective clothing for those who work with mutagenic agents. • Sunscreen for when the skin is exposed to UV radiation. • Vaccination against some viruses with links to certain cancers. Cancer – Hereditary Mutations • Routine screening for certain mutations, more screenings if the patient is a high risk. • Depends on the mutation. • Removing the organ that the mutation affects before the cancer develops. Genetic Disorders (Hereditary Mutations) • DNA analysis to look for mutations. In parents, DNA analysis can be done to determine if they are a carrier of a mutant gene. • Gene therapy – it is possible to treat symptoms of cystic fibrosis by inserting a normal copy of the mutated gene. • Parents can undergo pre-implantation genetic diagnosis before IVF treatment to prevent any offspring having the disease. Embryos are screened.
  10. 10.       Multi-cellular organisms (such as humans) are made up of many different cell types that are specialised for function. These specialised cells originated from stem cells. Stem cells are found in the embryo where they divide to become new cells and then become specialised. They are also found in some adult tissues where they can become cells that need to be replaced e.g. Red blood cells. Stem cells that can divide into any type of cell are called totipotent cells. Totipotent stem cells are only present in the embryos of humans, in adult life any stem cells can only differentiate into a few kinds of specialised cells. All stem cells in plants are totipotent.
  11. 11. Stem Cell Therapies Treating Diseases (possibilities so far!) Ethical Issues • Stem cells can divide into any cell type, so could be used to replace cells damaged by illness or injury. • Spinal cord injuries – to replace damaged nerve tissue. • Involves destruction of an embryo which could become a fetus if placed in a womb. • Some stem cell therapies exist for some diseases affecting the blood and immune system. • Heart disease and damage caused by heart attacks – to replace damaged heart tissue. • Some believe that from the moment of fertilisation, an individual has the right to life. • Bone marrow contains some stem cells that can differentiate into any type of blood cell. • Bladder conditions – used to grow whole bladders that are implanted to replace faulty ones. • Some have fewer objections to stem cells obtained from unfertilised embryos. • Bone marrow transplants can be used to replace faulty bone marrow in some patients that produce abnormal blood cells. • Respiratory diseases – donated windpipes can be stripped down to their simple collagen structure, then covered with stem cells to generate tissue. • Some believe stem cells should only be obtained from adult cells – however these stem cells are not totipotent. This technique has been used to treat leukaemia, and sickle cell anaemia. • Organ transplants – organs could be grown to provide new organs for people on waiting lists. • The decision makes in society must take into account everyone’s views when making descisions about scientific research.

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