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22 Cards in this Set
- Front
- Back
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why cant you see chromosomes when a cell is in interphase?
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its not dividing so the DNA is unwound and spread out in the nucleus. the dna forms long threads wound around protein molecules called histones |
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describe the structure of chromatin
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DNA forms long threads wound around histones |
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what happens during interphase?
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- proteins are made - cell organelles are replicated - respiration occurs - DNA is replicated - cant see anything |
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what happens to chromatin when a cell starts to divide by mitosis?
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coils up and folds to form chromosomes - chromosomes consists of two chromatids held together by a centromer |
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in what phase of interphase does DNA replicate?
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the S phase ( synthesis) -happens between two growth phases |
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when is asexual reproduction and advantage?
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why is mitosis important?
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produces genetically identical copies of parent cells |
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why is it important that mitosis produces genetically identical copies of parent cells?
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- repair - if cells die or are damaged they need to be replaced with identical cells - asexual reproduction - some plants reproduce asexually - all offspring identical good in non changing environments |
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what happens in prophase?
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- centrioles move to opposite poles and start to send out microtubules that stretch across cell - microtubules form a system of fibres called a spindle nuclear membrane breaks down so chromosomes are now free in cytoplasm |
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what happens in metaphase?
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- centromeres line up on spindle equator - centromeres divide forming two daughter chromosomes |
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what happens in anaphase?
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microtubules contract pulling daughter chromosomes to opposite poles |
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what happens in telophase?
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- spindle fibres break down - nuclear membrane re-forms around each group of chromosomes - centrioles divide so each daughter cell has two - cytoplasm constricts separating the cell in two |
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give 3 differences between benign and malignant tumours
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slow growing - rapid growing stay within one tissue - invade surrounding tissue don't spread- can spread through blood or lymph vessels and form new tumours else where not usually life threatening but can cause damage - life threatening unless treated early on when removed don't normally grow back - can grow back once removed |
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how do proto-oncogenes work?
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- code for receptor proteins in cell membrane - activate genes that stimulate cell division when they're activated by a specific growth factor - others produce the growth factors that activate the receptor proteins |
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how do oncogenes cause uncontrolled cell division? |
- produce uncontrolled amounts of growth factors |
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how do tumour suppressor genes work?
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- cause cells with damaged DNA to die |
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what happens if a tumour suppressor gene mutates?
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cells carry on dividing uncontrollably passing on mutated DNA to daughter cells |
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give 3 causes of cancer
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genetics - some proto-oncogenes are more likely to mutate than others. Genes BRCA1 and 2 increase chances of breast cancer age - had more years of exposure to environmental factors and more time for genes to mutate ionising radiation - contains large amounts of energy that can penetrate body cells and break bonds between DNA molecules UV radiation - enough energy to penetrate skin cells, breaks bonds in DNA of skin cells causing skin cancer chemicals - carcinogens can cause cancer, contained in cigarette smoke, asbestos fibres and diesel exhaust Viruses - HPV causes cervical cancer as they carry code for a protein interferes with tumour suppressor genes, passed on during sex |
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describe the process of meiosis
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- first meiotic division occurs forming two diploid cells - second meiotic division occurs forming 4 haploid cells |
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give the 3 forms chromosomes can be found in
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thread-like chromatin - during G1of interphase thread-like sister chromatids - during s phase of interphase condensed visible form - during prophase |
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why is meiosis important? |
- produces haploid gametes - full diploid number is restored during fertilisation - if gametes weren't haploid the chromosome number would double with every new generation |
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give 3 characteristics of someone with down's syndrome |
flatter head, smaller ears, protruding tongue, shorter than average, single fold across palm instead of two, problems such as heart defects, learning difficulties, happy disposition, affectionate, life expectancy of 60 |
