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Flashcards by Clelia Serra, updated more than 1 year ago
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Created by Clelia Serra
almost 9 years ago
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| Question | Answer |
| What determines the order of amino acids in a protein? | The order of nucleotide bases in a gene |
| How is RNA different to DNA? | - Sugar is a ribose sugar - Nucleotides form a single polypeptide strand - Uracil replaces thymine as a base |
| Role of mRNA | - single polynucleotide strand - 3 bases called codon - Made in the nucleus during transcription - Carries genetic code from the DNA in the nucleus to the cytoplasm where it is used to make a protein during translation |
| Describe tRNA | - Single polynucleotide strand folded into clover shape - Hydrogen bonds between specific base pairs hold the molecule in this shape - Each one has a specific sequence of three bases at one end; anticodon - Have an amino acid binding site at the other end - Found in the cytoplasm where it is involved in translation - Carries amino acids to ribosomes |
| Transcription | 1. DNA helicase act on a specific region of DNA to break hydrogen bonds between the bases. Causes the strands to seperate 2. RNA polymerase moves along one of the two strands of DNA, causing nucleotides on this strand to join to individuial complementary nucleotides from pool in the nucleus 3. adenine attaches to uracil as a complementary pair. 4. As RNA polymerase adds the nucleotides to build a strand of pre-mRNA the DNA strand rejoins behind it. 5. When RNA polymerase reaches stop codon it detaches and production of pre-mRNA is complete. |
| What is splicing (only eukaryotic cells) ? | -- non-functional introns are removed and functional exons are joined together - Once introns removed, remaining exons are rejoined |
| Why can the process of splicing allow up to 12 different proteins | When exons are rejoined, can be rejoined in any order. Can code for different proteins depending on the order they are combined |
| Why does mRNA leave the nucleus via the nuclear pore? | Too large to diffuse out of nucleus |
| Translation | - The mRNA attaches to a ribosome and tRNA carry amino acids to the ribosome - The tRNA with the complementary anticodon sequence moves to the ribosome and pairs up with codon on the mRNA - A second tRNA attaches itself to the next codon on the mRNA in the same way - The ribosome moves along mRNA. bringing together 2 tRNA molecules at one time - Enzyme and ATP needed to join the amino acids by a peptide bond on the tRNA - As the 3rd tRNA joins the ribosome, 1st is released from its amino acid and free to collect another one. - continues till full polypeptide chain is built up and reaches a stop codon |
| What allows many identical polypeptides to be built up at one time? | Many ribosome's can pass immediately behind the 1st |
| The genetic code is... | - degenerate - non-overlapping - universal |
| What is meant by the code being degenerate? | Many codons can code for one amino acid |
| What is meant by it being universal? | The same specific base triplets code for the same amino acids in all living things |
| What determines the cell structure and cell processes | Each cell caries the same genes. Not all genes are expressed Because different genes are expressed, different proteins are made, these modify the cell |
| What are transcriptional factors? | - Move from cytoplasm to the nucleus. - In the nucleus, they bind to a specific DNA site near the start of their target genes - Control expression by controlling the rate of transcription - Some are activators, increase the rate; can help RNA polymerase bind to the start of the target gene and activate transcription - Others are repressors, decrease the rate of transcription; bind to the start of target gene, preventing RNA polymerase from binding, stopping transcription |
| How does oestrogen act as a transcriptional factor? | 1. oestrogen is lipid soluble, so easily diffuses across cell membrane 2. An inhibitor blocks the site on the transcriptional factor which binds to DNA 3. Oestrogen binds to a receptor on the transcriptional factor 4. Oestrogen causes the receptor to change shape, releasing the inhibitor 5. Transcriptional factor enters the nucleus through nuclear pore 6. Transcriptional factor binds with DNA and begins the process of transcription |
| What is siRNA? | Short, double stranded sections of DNA that interfere with expression of specific genes -Small interfering RNA |
| How does siRNA interfere with translation? | 1. Double stranded RNA broken up into siRNA 2. One of the two strands combines with an enzyme 3. The siRNA strand binds to the target mRNA 4. The enzyme cuts the mRNA into smaller sections 5. So prevents expression of the specific gene as protein can no longer be made |
| How can changes to the base sequence in DNA arise? | - errors during DNA replication - Mutagenic agents |
| Why can sometimes substitution mutations not change the order of amino acids? | Some amino acids are coded for by more than one codon. Not all substitution mutations will result in a change to the amino acid sequence of the protein, some will still code for the same amino acid |
| Why do deletions lead to mutations? | The deletion of a base will change the number of bases present. This will cause a shift in all the codons after |
| Mutagenic agents: | - UV radiation - ionising radiation - chemicals - benzene - some viruses |
| How do mutagenic agents increase the rate of mutations? | 1. Acting as a base; can substitute for a base during DNA replication 2. Altering bases; can delete or alter bases 3. Changing the structure of DNA |
| What are genetic disorders | Inherited disorders caused by abnormal genes or chromosomes |
| What are hereditary mutations? | If the gamete containing a mutation for a genetic disorder or cancer is fertilised. The mutation can now be present in the new fetus |
| What is cancer? | If a cell divides uncontrollably the result is a tumour - a mass of abnormal cells. Tumours that invade and destroy surrounding cells are cancers |
| What is the role of tumour-suppressor genes? How can they cause a tumour? | They slow down cell division by producing proteins that stop cells dividing or cause them to self destruct. If a mutation occurs, the protein isn't produced, the cells can divide uncontrollably |
| What is the role of proto-oncogenes? How can they cause a tumour? | When functioning normally, stimulate cell division by producing proteins that make cells divide. If a mutation occurs the gene can become over-active. Simulates cells to divide uncontrollably. |
| What is an oncogene? | A mutated proto-oncogene |
| How can acquired cancer be prevented? | Protective clothing Sunscreen Vaccination High-risk individuals screened regularly to diagnose early |
| What are stem cells? | Unspecialised cells that develop into other types of cell. They divide to become new cells which then become specialised. |
| Where are stem cells found? | The embryo - where they become specialised cells Also in some adult tissue; stem cells in bone marrow can become red blood cells |
| What are totipotent cells? | Stem cells that can mature into any type of cell in an organism |
| Where are stem cells found in plants? | In the areas where the plant is still growing |
| Why can stem cells in plants be used to grown plant organs? Why cant humans also do this? | All of them are totipotent. Compared to humans that only have totipotent cells in the embryo, mature humans have stem cells that can only differentiate into a few types of cell |
| How do totipotent cells become specialised? | 1. They all contain same genes, during development not all of them are transcribed and translated. 2. Under the right conditions, some genes are expressed and others are switched off. 3. mRNA is only transcribed from specific genes 4. The mRNA of these genes are translated into proteins. 5. These proteins modify the cell - determine cell structure and control the cell. 6. Changes to the cell caused by these proteins cause the cell to become specialised. |
| How can tissue culture be used to grow plants from a totipotent cell? | 1. Single cell taken from growing area on a plant 2. Cell placed in growth medium that contains nutrients and growth factors. 3. The plant cell will grow and divide into a mass of unspecialised cells. If the conditions are suitable, the cells will mature and develop into specialised cells 4. The cells grow and specialise to form a plant organ or an entire plant depending on the growth factors used |
| Why is the growth medium sterile? | So that micro-organisms cannot grow and compete with the plant cells |
| What type of stem cells does bone marrow contain? | Stem cells that can specialise to form any blood cell |
| Where are the potential sources of human stem cells? | Adult and embyonic |
| What is the disadvantage of using adult stem cells over embryonic? | They can only specialise into a limited range of cells |
| What are embryonic stem cells? How are embryo's created? | Obtained from embryo's at early stages of development. Embryo's created in a lab using IVF - outside of the womb Once they are 4-5 days old stem cells are removed and the rest of the embryo is destroyed. |
| Ethical issues with using stem cells: | - Destroying embryo that could become a fetus if placed in the womb - At the moment of fertilisation, an individual is formed that has the right to life - Can obtain stem cells from unfertilised embryo's made from egg cells that haven't been fertilised by sperm as they wouldn't survive |
| What are the 3 ways DNA fragments can be produced? | - Using reverse transcriptase - Using restriction endonuclease - Using PCR |
| What are the 5 processes of making a protein using DNA technology of gene transfer and cloning | 1. Isolation 2. Insertion 3. Transformation 4. Identification 5. Growth/cloning |
| Why use reverse transcriptase? | Many cells contain only two copies of each gene, difficult to obtain a DNA fragment containing the target gene. They can contain many mRNA molecules which is complementary to the gene |
| What does reverse transcriptase make? | Makes DNA from an RNA template |
| What is the DNA made in this way called? | cDNA |
| How is cDNA made? | mRNA extracted form cells. Then it's mixed with free DNA nucleotides and reverse transcriptase. The reverse transcriptase uses mRNA as a template to synthesise a new strand of cDNA. DNA polymerase is used to join complementary nucleotides |
| What do restriction endonucleases recognise? | Specific palindromic sequences of nucleotides - antiparallel base pairs |
| What does the restriction endonuclease do when they reach a palindromic sequence | Cuts and digests the DNA at all these places |
| Why do different restriction endonucleases cut at different specific recognition sequences | Because the shape of the recognition sequence is complementary to an enzyme's active site |
| What does sticky ends allow? | Binding of the DNA fragment to another piece of DNA that has sticky ends with complementary sequences |
| What is PCR used for? | To make millions of copies of a fragment of DNA in a few hours. - automated - Rapid - Efficient |
| What is needed for PCR | - DNA fragment - this is being copied - DNA polymerase - Join together nucleotides - Primers - short sequences of nucleotides - Nucleotides - each of the 4 bases - Thermocycler |
| What is a primer, what are they needed for? | Short sequence of nucleotides that have a set of bases complementary to those at the end of each of the two fragments. - Provide a starting sequence for DNA polymerase to begin DNA cloning. As DNA polymerase can only attach nucleotides to the end of an existing chain. - Prevent the strands rejoining |
| Describe the process of the PCR | 1. The DNA mixture (DNA sample, free nucleotides, primers, DNA polymerase) is heated to 95 °C in the thermocycler to break hydrogen bonds between strands. 2. The mixture is then cooled to allow the primers to anneal . 3. Reaction mixture then heated to 72° so that DNA polymerase is at it's optimum, and can line up the free nucleotides alongside each template strand, attaches starting at the primers on both strands. 5. Specific base pairing means that new complementary strands are formed 6. Two new copies of the fragment of DNA are formed and the cycle is complete. 7. Cycle starts again with mixture heated to 95° with 4 strands as templates. |
| Remember... | Each PCR cycle doubles the amount of DNA |
| What's the difference between in vivo and in vitro cloning? | Vitro - copies are made outside of a living organism Vivo - copies are made within a living organism, as the organism grows and divides, it replicates its DNA, creating multiple copies |
| Why are sticky ends important? | Can combine the DNA of one organism with that of another organism |
| What happens during stage one of in vivo cloning? | The Gene is inserted into the vector - Once fragment is cut, using restriction endonucleases, it is inserted into a vector (plasmid) - The vector is cut open using the same restiction endonuclease that was used to isolate the DNA fragment - The sticky ends of the vector are complementary to the sticky ends on the gene - Vector DNA and DNA fragment are mixed together with DNA ligase. - DNA ligase joins the sticky ends of the fragment to sticky ends of the vector - The new combination of bases in the DNA is called recombinant DNA |
| What is recombinant DNA | Vector DNA + DNA fragment |
| How is the gene in the vector transferred into the host cell | 1. The vector with the recombinant DNA is used to transfer the gene into cells 2. When a plasmid is used, host cells, host cells have to be persuaded to take in the plasmid vector and its DNA. Host bacterial cells are placed into ice-cold calcium chloride to make their cell walls more permeable. |
| Which genes are easily identifiable? | - resistant to an antibiotic - Make a fluorescent protein - Produce an enzyme who's action can be identified |
| How is an anti-biotic resistance gene marker used? | - Use another antibiotic gene in plasmid -The gene that was cut in order to incorporate the required gene - When the gene is cut, it can no longer produce enzyme that breaks down the bacteria - Can identify which ones are resistant. - The ones that have taken up the gene will be destroyed, so need to use replica plating |
| Describe the stages of detecting transformed bacteria | 1. Host cells and plasmid vectors sample is transferred to nutrient agar plate with first antibioitic 2. Colonies are able to develop 3. Colonies only grow from cells that are resistant to the first antibiotic. The cells in there colonies have taken up plasmids. 4. Replica plate is made 5. Nutrient agar plate with second antibiotic. 6. Colonies are allowed to develop 7. Missing colony has lost resistance to second antibiotic and is therefore the one which has cells incorporating the new gene |
| Describe the use of fluorescent markers | - more rapid - Transfer GFP from jellyfish into plasmid - The gene that is cloned is placed in the middle of GFP gene - Bacteria containing the plasmid with the gene to be clones will not be able to produce GFP -They will not fluoresce - Can be viewed under the microscope |
| Advantages of in vivo | 1. Cloning can produce mRNA and protein as well as DNA because it is done in a living cell so has the ribosomes and enzymes 2. Can produce modified DNA, modified mRNA, modified protein 3. Large fragments of DNA can be cloned 4. Very low risk of contamination 5. I produces transformed bacteria |
| Disadvantages of vivo | - DNA fragment has to be isolated from other cell components - you may not want modified DNA - Slow process (bacterial grow quite slowly) |
| Advantages of in vitro (PCR) | - Used to produce lots of DNA - DNA isn't modified - only replicates the DNA fragment of interest, don't, have to isolate DNA fragment form host cell - fast - does not require living cells - No complex cutting techniques |
| Disadvantages of in vitro | - only replicate small DNA fragments - expensive |
| Benefits of GM organisms in agriculture | - Transformed so that they give higher yields or are more nutritious - Reduced risk of famine and malnutrition - pest resistance, fewer pesticides |
| Ethical concerns with GM products in industry | - Without proper labelling, some people think they wont have the choice whether to consume GM products - people worried about processes used to purify proteins could lead to the introduction of toxins into the food industry |
| How can genetic engineering benefit people | - agricultural crops - transformed crops - Medicines |
| What part of DNA is used to make a genetic fingerprint? | The repetitive, non-coding base sequences - base sequences that don't code for proteins and repeat next to each other over and over |
| Why does this lead to a unique fingerprint? | The repeated exons occur in lots of places in the genome. The number of times a sequence is repeated at different places on their genome can be compared. |
| Why is the probability of two people having the same fingerprint very low? | The probability of two individuals having the same genetic fingerprint is very low because the chance of 2 individuals having the same number of sequence repeats at each place found on DNA is very low |
| What are the main stages in making a genetic figerprint | 1. Extraction 2. Digestion 3. Separation 4. Southern blotting 5. Hybridisation 6. Development |
| How do you extract the DNA? | From a person's blood, saliva Then separated from the rest of the cell. Quantity increased using PCR |
| How is the DNA cut into fragments? | - Using restriction endonucleases They are chosen to cut close to, but not within groups of core sequences |
| How is PCR used in GF? | - To make many copies of the areas of DNA that contain the repeated sequences - Primers are used that bind to either side of these repeats so the whole repeat is amplified |
| What does the length of fragments correspond to? | The number of repeats the person has at each specific position |
| How are the fragments then separated? | Separated according to size using gel electrophoresis |
| Describe gel electrophoresis | -The DNA mixture is placed into a well in gel and covered in a buffer solution. - An electrical current is passed through the gel - DNA fragments are negatively charged, so move towards the positive electrode at the far end of the gel - The small DNA fragments move faster and travel further |
| Describe how southern blotting allows you to make a copy of the fingerprint | - The gel is immersed into alkali to separate the double strands into single strands - Thin nylon membrane laid over gel - Membrane covered in sheets of absorbent paper draws up the liquid containing the DNA by capillary action - Transfers the DNA fragments to the nylon membrane in the same positions as they were on the gel. - Fragments fixed to the membrane using UV light |
| How can the fragments then be identified? | - Radioactive or fluorescent DNA probes are used to bind with the core sequences - The probes have base sequences which are complementary to the core sequences - They then bind to the under specific conditions - Process carried out with different probes each binds to a different core sequence. |
| How is the fingerprint finally developed? | An x-ray film is put over the nylon membrane - The film is exposed by radiation from radioactive probes |
| How are the fingerprints compared? | If both fingerprints have a band at the same location on the gel, it means they have the same number of nucleotides and the same number of sequence repeats at that place. |
| What can genetic fingerprinting be used for? | - Determining genetic relationships; we inherit the repetitive, non-coding base sequences from our parents - Determining genetic variability within a population; the greater the number of bands that don't match on a genetic fingerprint, the more genetically different people are. |
| Why does matching fingerprints at a crime scene not necessarily mean they did the crime? | - DNA may belong to close relative - Sample contaminates - Chemicals could inhibit some of the restriction endonucleases; fail to cut some sections of DNA |
| What can DNA probes be used for? | - To locate genes or see if a person's DNA contains a mutated gene |
| What are DNA probes? | Short strands of DNA that have a specific base sequence that's complementary to the base sequence of part of a target gene |
| How is restriction mapping carried out? | 1. Different restriction enzymes are used to cut labelled DNA into fragments 2. The DNA fragments are then separated by gel electrophoresis 3. The size of the fragments produced is used to determine the relative locations of cut sites 4. A restriction map of the original DNA is made - a diagram of the piece of DNA showing the different recognition sites of the restriction enzymes are found. |
| What is a partial digest | Where the restriction enzymes haven't been left long enough to cut all their recognition sequences, producing fragments of other lengths |
| What is a total digest? | - Where both enzymes are present and the DNA is cut at all of the recognition sequences present |
| How is the distance between the different recognition sites determined? | By the pattern of fragments produced |
| What needs to be set up in the 4 test tubes for DNA sequencing | 1. Many single stranded fragments of DNA to be sequenced 2. A mixture of free nucleotides 3. A small quantity of one of the 4 terminator nucleotides. 4. A radioactively primer to start process of DNA synthesis 5. DNA polymerase |
| Why is the addition of a normal or terminator nucleotide equally likely? | As binding of nucleotides is random |
| Key points with sequencing: | - The DNA fragments in each test tube can be varying lengths depending on when the terminator nucleotide attaches - All DNA fragments will end in the same nucleotide with the same base - The fragments will be identified because primer on the other end is labelled with dye or radioactively |
| What are the modern techniques for sequencing and mapping? | - automatically carried out using machines - Computers use fluorescent dye - Each base different colour - DNA synthesis in 1 test tube - uses PCR - electrophoresis results scanned by lasers |
| What is a DNA microarray, and how does it work? | - A glass slide with microscopic spots of different DNA probes attached to it. - A sample labelled human DNA washed over it - If the labelled DNA contains any DNA sequences that match any of the probes, it will stick to the array - The array is washed to remove any labelled DNA that hasn't stuck to it. - The array is then visualised under UV light, any labelled DNA attached will fluoresce. - Any parts that do fluoresce means that the persons DNA contains that specific gene |
| How is a probe made? | First the gene that you want is sequenced Then PCR is used to to produce multiple copies of part of the gene |
| What is genetic counselling? | Advising patients and their relatives about the risks of genetic disorders |
| Why during genetic counselling would you advise about screening? | Can help identify the carrier of a gene, the type of mutated gene they're carrying, and finding the most affective treatment |
| What is gene therapy? | - Altering the defective genes (mutated alleles) inside cells to treat genetic disorders and cancer |
| What determines the type of gene therapy? | If the disorder is cause by a dominant or recessive allele |
| What do you do if dominant? | silence the dominant allele e.g. by sticking a bit of DNA in the middle of the allele so it doesn't work anymore |
| If it's caused by two recessive allele? | Add the working dominant allele to make up for them |
| How do you get a new allele inside the cell? | 1. Using vectors 2. Different vectors can be used viruses, plasmids, liposomes |
| What is somatic cell therapy? | Altering the alleles in body cells, particularly cells most affected by the disorder. e.e for cystic fibrosis, somatic cell therapy targets the epithelial cells lining the lungs. Doesn't affect sex cells, so offspring can still inherit |
| What is germ line therapy? | Altering the alleles in sex cells. Every cell of any offspring produced from these cells will be affected by the gene therapy and wont suffer from the disease |
| Disadvantages of gene therapy? | - Somatic; short lived - Somatic; undergo multiple treatments - Difficult to get the allele into specific body cells - Body could identify vectors as being non-self and start an immune response - An allele could be inserted into the wrong place of the DNA - An inserted allele could be over expressed producing too much of the missing protein - Disorders caused by multiple genes would be difficult to treat with this technique - Gene isn't always expressed. - Not effective for treating conditions that arise in more than one gene |
| Advantages of gene therapy? | - It could prolong the lives of people with genetic disorders and cancer - It could give people with genetic disorders a better quality of life - Germ line; carriers might be able to conceive baby without the disorder or risk of cancer - Germ line; could decrease the number of people that suffer from genetic disorders and cancer |
| Ethical issues with GT | Worried it will be used in other ways other than medical treatment. e.g cosmetics May do more harm than good |
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