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98 Cards in this Set
- Front
- Back
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What is DNA and what is it made up of? |
-it is a polynucleotide-made up of lots of nucleotides joined together -each nucleotide is made from a PENTOSE SUGAR, a PHOSPHATE group and a NITROGENOUS BASE |
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What is the sugar is the DNA nucleotides called? |
-a deoxyribose sugar -each nucleotide has the same sugar and phosphate but the base on each nucleotide can vary |
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What are the 4 possible bases? |
-Adenine -Thymine -Cytosine -Guanine |
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Draw the basic structure of a DNA nucleotide |
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What do the nucleotides join together to make? |
-polynucleotide strands |
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How do they make polynucleotide strands? |
-the nucleotides join up between the phosphate group of one molecule and the sugar of another, creating a sugar-phosphate backbone -2 DNA polynucleotide strands join together by hydrogen bonds between the bases |
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How do the bases then join up? |
-each base can only join with one particular partner-specific base pairing -Adenine always pairs with thymine -Guanine always pairs with cytosine |
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What happens lastly? |
-the two stands wind up to form the DNA double-helix |
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Draw a diagram of two joined polynucleotide strands? |
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What does DNA contain? |
-our genetic information-all the instructions needed to grow and develop from a fertilised egg to a fully grown adult
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How does DNAs structure make it good at its job? |
-the DNA molecules are v long and are coiled up very tightly, so a lot of genetic information can fit into a small space in the cell nucleus -DNA molecules have a paired structure, which makes it much easier to copy itself-this is called self replication-it is important for cell division+for passing genetic information from generation to generation -the double-helix means that the DNA is v stable in the cell |
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What is the DNA like in eukaryotic cells? |
-these cells contain linear DNA molecules that exist as chromosomes-thread like structures, each made up of one long molecule of DNA -the DNA molecule is really long, so has to be wound up to fit into the nucleus -the DNA molecule is wound around proteins(histones) -histone proteins also help support the DNA -the DNA is then coiled up v tightly to make a compact chromosome |
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What is the DNA like in prokaryotic cells? |
-they also carry the DNA as chromosomes but the DNA molecule are shorter and circular -the DNA isnt wound around proteins-it condenses to fit into the cell by supercoiling |
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How are genes instructions for proteins? |
-genes are sections of DNA which are found on chromosomes -genes code for proteins-they contain the instructions to make them -proteins are made from amino acids -diff proteins have a diff number and order of amino acids -its the order of nucleotide bases in a gene that determines the order of amino acids in a particular protein |
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How is each amino acid then coded for? |
-by a sequence of three bases-called a triplet code, in a gene -different sequences of bases code for different amino acids |
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How is it, that not all of the DNA in eukaryotic cells codes for proteins? |
-genes in eukaryotic DNA contain sections that don't code for amino acids -these sections of DNA are called introns (the bits that do code for DNA are called exons) -introns are removed during protien synthesis -eukaryotic DNA also contains regions of multiple repeats outside of genes -these are DNA sequences that repeat over and over -these areas don't code for amino acids either
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What is the purpose of introns? |
-their purpose isn't known for sure |
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What is the function of enzymes in humans? |
-enzymes speed up most of our metabolic pathways-the chemical reactions that occur in the body -these pathways determine how we grow and develop |
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Therefore, how does DNA determine our nature and development? |
-bc enzymes control the metabollic pathways, they contribute to our development, and ultimately what we look like (our phenotype) -all enzymes are proteins, which are built using the instructions contained within genes -the order of bases in the gene decides the order of amino acids in the protein and so what type of protein is made -so, our genes help to determine our nature, development, and phenotype bc they all contain the info to produce all our proteins and enzymes |
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What are alleles? |
-when genes can exist in more than one form. These forms are called alleles |
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How do alleles work? |
-the order of bases in each allele is slightly different,s o they code for slightly different versions of the same characteristic |
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What are pairs of matching chromosomes called? |
-homologous pairs -in a homologous pair, both chromosomes are the same size and have the same genes, although they could have different alleles -alleles coding for the same characteristic will be found at the same position on each chromosome in a homologous pair |
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What are mutations? |
-they are changes in the base sequence of an organisms DNA |
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Therefore, what can mutations do? |
-they can produce new alleles of genes -a gene codes for a particular protein, so if the sequence of bases in a gene changes, a non-functional or different protein could be produced -all enzymes are proteins. if there's a mutation in a gene that codes for an enzyme, then that enzyme may not fold up properly. This may produce an active site that's the wrong shape and so a non-functional enzyme |
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What are antibiotics? |
-chemicals that either kill or inhibit the growth of bacteria -different types of antibiotics kill or inhibit the growth of bacteria in different ways |
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What are they two ways of doing this? |
-some prevent growing bacterial cells from forming the bacterial cell wall, which usually gives the cell structure and support -this can lead to osmotic lysis |
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Describe osmotic lysis |
-the antibiotics inhibit enzymes that are needed to make the chemical bonds in the cell wall -this prevents the cell from growing properly and weakens the cell wall -water moves into the cell by osmosis -the weakened cell wall can't withstand the increase in pressure and bursts (lysis) |
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How do mutations in bacterial DNA cause antibiotic resistance? |
-the genetic material in bacteria is the same as in most other organisms-DNA -the DNA of an organism contains genes that carry the instructions for different proteins -these proteins determine the organisms characteristics -mutations are changes in the base sequence of the DNA -if a mutation occurs in the DNA of a gene it could change the protein and cause a different characteristic some mutations in bacterial DNA mean the bacteria are not affected by a particular antibiotic-they developed antibiotic resistance |
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What happens with methicillin for example? |
-it is an antibiotic that inhibits an enzyme involved in cell wall formation -some bacteria have developed resistance to methicillin -usually resistance to methicillin occurs bc the gene for the target enzyme of methicillin has mutated -the mutated gene produces an altered enzyme that methicillin no longer recognises and so can't inhibit |
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What is vertical gene transmission? |
-when genes are passed on during reproduction |
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Describe vertical gene transmission? |
-bacteria reproduce asexually-so each daughter cell is an exact copy of the parent -this means that each daughter cell has an exact cope of the parents cells genes, including any that give it antibiotic resistance -genes for antibiotic resistance can b found in the bacterial chromosome or in plasmids rings of DNA found in bacterial cells -the chromosome and any plasmids are passed on to the daughter cells |
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Describe horizontal gene transmission |
-genes for resistance can also be passed on horizontally -two bacteria join together in a process called conjugation and a copy of a plasmid is passed from one cell to the other -plasmids can be passed on to a member of the same species or a totally different species |
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How can an adaptation like antibiotic resistance become more common in a population? |
-because of natural selection |
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How does this natural selection work? |
-individuals within a population show variation in their characteristics -predation, disease and competition create a struggle for survival -individuals with better adaptations are more likely to survive, reproduce and pass on the alleles that cause the adaptation to their offspring -over time, the no of individuals with the advantageous adaptations increases -this leads to evolution as the favourable adaptations become more common in the population |
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Therefore, how do populations of antibiotic-resistant bacteria evolve by NS? |
-some individuals in a population have alleles that give them resistance to an antibiotic -the population is exposed to that antibiotic, killing bacteria without the antibiotic resistance allele -the resistant bacteria survive and reproduce without competition, passing on the allele that gives antibiotic resistance to their offspring -after time, most organisms in the population will carry the ABR allele |
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Give some adaptations that could increase the chance of survival |
-streamlined body, camouflage, larger paws for running quicker -streamlined body, camouflage, larger paws for running faster, larger claws, longer neck -shorter/longer hairs, large ears, increased water storage capacity |
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How would streamlined body, camouflage, larger paws for running quicker increase survival? |
-help to escape from predators |
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How would streamlined body, camouflage, larger paws for running quicker, larger claws and longer neck increase survival? |
-help catch prey/get food |
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How would shorter/longer hairs, large ears, increased water storage capacity increase survival? |
-make the animal more suited to the climate |
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Give an example of two bacterial infections that antibiotic resistance has made difficult to treat? |
-TB -MRSA |
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Describe TB |
-is a lung disease caused by bacteria -one a major killer in UK -no. of people dying from TB decreased bc of development of specific antibiotics that killed the bacterium -recently some populations of TB have evolved resistance to the most effective antibiotics -NS has lead to populations that are resistant to a range of antibiotics=MULTIDRUG-RESISTANT |
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How do they now treat TB? |
-taking a combination of antibiotics for about 6 months -but it is becoming harder to treat as mulit-drug resistant strains are evolving quicker than drug companies can develop new antibiotics |
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Describe MRSA |
-it is a strain of bacteria that has evolved to be resistant to a number of commonly used antibiotics including methicillin -causes a range of illnesses from minor skin infections to life-threatening diseases eg meningitis and septicaemia |
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What is the major problem with MRSA? |
-some strains are resistant to nearly all the antibiotics that are available -it can take a long time for clinicians to determine which antibiotics if any will kill the strain of each individual is infected with-during this time the patient could even die -drug companies are trying to develop alternative ways of treating MRSA |
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Give one example of a scientific finding that could slow down NS and how scientists can act upon them |
-knowledge: using an antiseptic gel to wash hands can help to reduce the spread of infectious diseases by person-to-person contact -decision: health workers should reduce spread by washing their hands with antiseptic gel before and after visiting each patient on a ward |
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Give another example of a scientific finding that could slow down NS and how scientists can act upon them |
-Knowledge: bacteria become resistant to antibiotics more quickly when antibiotics are misused and patients don't finish the course -decision: doctors should only prescribe antibiotics when absolutely necessary. Patients have to be told the importance of finishing all the antibiotics even if they start to feel better |
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What is the first ethical issue surrounding the use of antibiotics? |
-some people believe that antibiotics should only be used in life-threatening situations to reduce the increase of resistance. Others argue against this because people would take more time off work for illness, it could reduce peoples standard of living, it could increase the incidence of disease and cause unnecessary suffering |
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What is the second ethical issue surrounding the use of antibiotics? |
-a few people believe doctors shouldn't prescribe antibiotics to those suffering dementia. They argue that they may forget to take them, increasing the chance of resistance developing. However some people argue that all patients have the right to medication |
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What is the third ethical issue surrounding the use of antibiotics? |
-some argue that terminally ill patients shouldn't receive antibiotics because they're going to die. But withholding antibiotics from these patients could reduce their length of survival and quality of life |
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What is the third ethical issue surrounding the use of antibiotics? |
-some believe animals shouldn't be given antibiotics(bc it may increase antibiotic resistance) -other people argue that this could cause unnecessary suffering to the animals |
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What is the cell cycle? |
-the process of cell growth and divison -it is the process that all body cells from multicellular organisms use to grow and divide |
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How does the cell cycle work? |
-it starts when a cell has been produced by cell division and ends with the cell dividing to produce two identical cells -it consists of a period of cell growth and DNA replication, called interphase, and a period of cell division called mitosis -interphase is subdivided into three separate growth stages = G1,S, G2 |
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Describe G1-Gap phase 1 |
-the cell grows and new organelles and proteins are made |
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Describe S-synthesis |
-cell replicates its DNA, ready to divide by mitosis |
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Describe G2-Gap phase 2- |
-cell keeps growing and proteins needed for cell division are made |
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Then what does it return to? |
-mitosis-the cycle starts and ends here |
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What happens in interphase? |
-DNA is replicated -DNA copies itself before cell division so that each new cell has the full mount of DNA |
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Describe the first stage of interphase |
-the enzyme DNA helicase breaks the hydrogen bonds between the two polynucleotide DNA strands -the helix unzips to form two single strands |
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Describe the second stage of interphase |
-each original single strand acts as a template fro a new strand. Free-floating DNA nucleotides join to the exposed bases on each original template strand by specific base pair-A+T and C+G |
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Describe the third stage of interphase |
- the nucleotides on the new strand are joined together by the enzyme DNA polymerase -H bonds from between the bases on the original and new strand |
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Describe the fourth stage of interphase |
-each new DNA molecule contains one strand from the original DNA molecule and one new strand
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What is this type of copying called? |
-semi-conservative replication because half of the strands in each new DNA molecule are from the original piece of DNA |
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What happens during mitosis and what is it? |
-it is the form of cell division that occurs during the cell cycle -a parent cell divides to produce two genetically identical daughter cells-contain an exact cope of the DNA of the parent cell -it is needed for the growth of multicellular organisms and for repairing damaged tissues |
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What are the stages of mitosis? |
-prophase -metaphase -anaphase -telophase
-interphase comes before mitosis
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Describe interphase |
-the cell carries out normal functions, but also prepares to divide. The cells DNA is unravelled and replicated, to double its genetic content. The organelles are also replicated so it has spare ones, and its ATP content is increased-need to provide the energy for cell division |
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Describe prophase |
-the chromosomes condense, getting shorter and fatter -tiny bundles of protein called centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle -the nuclear envelope (the membrane around the nucleus) breaks down and chromosomes lie free in the cytoplasm |
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Describe metaphase |
-the chromosomes (each with 2 chromatids) line up along the middle/equator of the cell and become attached to the spindle by their centromere |
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Describe anaphase |
-the centromeres divide, separating each pair of sister chromatids -the spindles contract, pulling chromatids to opposite ends of the cell, centromere first |
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Describe telophase |
-the chromatids reach the opposite poles on the spindle -they uncoil an become long and thin again-they're now called chromosomes again -a nuclear envelope forms around each group of chromosomes, so there are now two nuclei -the cytoplasm divides and there are now 2 daughter cells that are genetically identical to the original cell and to each other |
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What happens then? |
-mitosis is finished and each daughter cells starts the interphase part of the cell cycle to get ready for the next round of mitosis |
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What is cancer? |
-the result of uncontrolled cell division -cell growth and cell division are controlled by genes -normally when cells have divided enough times to make enough new cells, they stop -but if there is a mutation in a gene that controls cell division, the cells can grow out of control -the cells keep on dividing to make more and more cells which can form a tumour -cancer is a tumour that invades the surrounding tissue |
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What are cancer treatments designed to do? |
-disrupt the cell cycle -these treatments don't distinguish tumour cells from normal cells though-they also kill normal body cells that are dividing -however, tumour cells divide much more frequently than normal cells, so the treatments are more likely to kill tumour cells |
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Give an example of a cell cycle target of cancer treatment? |
-G1 (cell growth and protein production)- some chemical drugs (chemotherapy) prevent the synthesis of enzymes needed for DNA replication. If these aren't produced the cell is unable to enter the synthesis phase (s), disrupting the cell cycle and forcing the cell to kill itself -S phase (DNA replication)- radiation and some drugs damage DNA. When the cell gets to the S phase it checks for damaged DNA and if any is detected it kills itself, preventing further tumour groth |
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What are the steps taken to reduce the impact on normal body cells? |
-chunk of tumour is removed first using surgery which removes a lot of tumour cells and increases access of any left to nutrients and o2, which triggers them to enter the cell cycle, making them more susceptible to treatment |
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Give another step taken? |
-repeated treatments are given with periods of non-treatment in between -a large dose could kill all the tumour but also so many normal cells that the patient could die. -breaks in between allow the body to recover and produce new cells -the treatment is repeated as any tumour cells not killed by the treatment will keep dividing and growing during the breaks too -the break period is kept short so the body can recover but the cancer can't grow back to the same size as before |
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Look at interpreting early experimental work about DNA |
SEE TEXT BOOK |
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How is DNA from one generation passed to the next? |
-by gametes -gametes are the sperm cells in males and egg cells in females. They join together at fertilisation to form zygote, which divides and develops into a new organism |
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What do normal body cells have? |
-the diploid number (2n) of chromosomes-meaning that each cell contains two of each chromosome, one from the mum and one from the dad |
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What do gametes have? |
-haploid (n) number of chromosomes-there's only one copy of each chromosome |
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What happens at fertilisation? |
-a haploid sperm fuses with a haploid egg, making a cell with the normal diploid number of chromosomes. Half these chromosomes are from the father (the sperm) and half are from the mother (egg) |
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What is meiosis? |
-a type of cell division -cells that divide by meiosis are diploid to start with, but the cells that are formed from meiosis are haploid-the chromosome number halves -without meiosis, you'd get double the number of chromosomes when the gametes fused |
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Describe meiosis |
-the DNA unravels and replicates so there are two copies of each chromosome, called chromatids -the DNA condenses to from double-armed chromosomes, made from two sister chromatids -Meiosis 1 (1st division)-the chromosomes arrange themselves into pairs -these homologous pairs are then separated, halving the chromosome number -meiosis 2 (2nd division)-the pairs of sister chromatids that make up each chromosome are separated -4 haploid cells (gametes) that are genetically different from each other are produced |
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How does crossing over happen in MEOSIS 1? |
-During meiosis 1, homologous pairs of chromosomes come together and pair up -the chromatids twist around each other and the bits of chromatids swap over -the chromatids still contain the same gens but now have different combinations of alleles
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How does the crossing over of chromatids produce cells that are genetically different? |
-the crossing over of chromatids in meiosis 1 means that each of the 4 daughter cells formed from meiosis contain chromatids with different alleles -the homologous pairs come together -chromatids cross over -one chromosome from each homologous pair ends up in each cell -each cell has a different chromatid and therefore a different set of alleles, which increases genetic variation |
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What also leads to genetic variation? |
-independent segregation of chromosomes |
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Describe how independent segregation of chromosomes creates genetic variation |
-the 3 daughter cells formed from meiosis have completely different combinations of chromosomes -all your cells have a combination of chromosomes from your parents, half from mum,half from dad -when the gametes are produced, different combinations of those maternal and paternal chromosomes go into each cell -this is called independent segregation... |
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How can variation in DNA lead to genetic diversity? |
-genetic diversity exists within a species. The DNA within a species varies v little though as all the members of the species will have the dame genes but different alleles -the DNA of different species varies a lot. Members of different species will have different genes. The more related a species is, the more DNA they share |
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What is diversity within a population increased by? |
-mutations in the DNA-forming new alleles -different alleles being introduced into a population when individuals from another population migrate into them and reproduce=gene flow |
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What are genetic bottlenecks? |
-they reduce genetic diversity -it is an event that causes a big reduction in a population -this reduces the number of different alleles in the gene pool and so reduces genetic diversity -the survivors reproduce and a larger population is created from a few individuals |
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What is the founder effect?
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-it describes what happens when just a few organisms from a population start a new colony
-only a small number of organisms have contributed their alleles to the gene pool -theres more inbreeding in the new population, which can lead to a higher incidence of genetic disease |
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Give an example-the amish
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-the Amish population of NA are all descended from a small no. of swiss who migrated there
-the population shows little genetic diversity -they have remained isolated from the surrounding population due to their religious beliefs, so few new alleles have been introduced -the population suffers an unusually high incidence of genetic disorders |
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How can the founder effect occur?
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-as a result of migration leading to geographical separation or if a new colony is separated from the original population for another reason, eg religion
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How can genetic diversity also be reduced?
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-by selecting breeding of planta and animals by humans
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What is selective breeding?
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-it involves humans selecting which domesticated animals or strains of plants reproduce together in order to produce high-yeilding breeds
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Give an example of this for a farmer wants a strain of corn plant that is tall and produces lots of ears
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-breeds together a tall corn strain and one that produces multiple ears
-he selects the offspring that are tallest and have most ears, and breeds them together -the farmer continues this until he produces a v tall strain that produces multiple ears of corn |
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How does this lead to a reduction in genetic diversity?
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-once and organism with the desired characteristics has been produced, only that type of organism will continue being bred
-so only similar organisms with similar traits and therefore similar alleles are bred together -it results in a type of genetic bottleneck as it reduces the no. of alleles in the gene pool |
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What are the arguments FOR selective breeding?
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-it can produce high-yeilding animals and plants
-it can be used to produce animals and plants that have increased resistance to disease which means that farmers have to use fewer drugs and pesticides -animals and plants could be bred to have increased tolerance of bad conditions eg. drought/cold |
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What are the arguments AGAINST selective breeding?
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--it can cause health problems
-it reduces genetic diversity, which results in an increased incidence of genetic disease and an increased susceptibility to new diseases bc of the lack of alleles in the population |
