Introns are sections of DNA that do not code for anything.
Sometimes they are in the middle of genes and sometimes they come between different genes.
Due to these introns very little of DNA has a code that actually makes proteins.
Monday, 10 March 2014
Wednesday, 26 February 2014
The importance of meiosis in producing cells which are genetically different. Within this unit, meiosis should be studied only in sufficient detail to show • the formation of haploid cells • independent segregation of homologous chromosomes. Gametes are genetically different as a result of different combinations of maternal and paternal chromosomes • genetic recombination by crossing over.
Meiosis is the process by which sex cells (gametes) are produced. They have half the genetic information of a normal (somatic) cell.
The 'normal' amount of chromosomes is called the diploid number (in humans it is 46 chromosomes/23 pairs of chromosomes) and gametes have the haploid number of chromosomes (23 in humans).
It is important that gametes have half the genetic information so that when two gametes meet the child gets a mixture of genes from its parents and therefore is very different. This is called variation and is what has enabled evolution to happen.
Haploid cells are made in two stages: meiosis 1; and meiosis 2:
Prophase 1: chromatin condenses to form chromosomes. Homologous pairs (the same chromosomes, one from your mum and one from your dad) come together, here some segments of DNA can transfer from one into another, so alleles will swap- this is called crossing over and increases variation. Nuclear envelope and nucleolus dissolve. Spindle fibres start to form and chromosomes move to the poles.
Metaphase 1: homologous pairs line up in the middle of the cell, some of the paternal chromosomes are on the right and some on the left, the same for maternal chromosomes.
Anaphase 1: the pairs are pulled apart towards the opposite poles by spindle fibres.
Telophase1 : the nuclear envelope and nucleus reform (and cytokineses happens) so two new cells have been made. Because some of paternal and maternal DNA was in a random order, the cells have different DNA, this is called independent segregation.
Meiosis 2 happens in both of the cells formed by meiosis 1, it is the same as mitosis:
Prophase 2: nuclear envelope and nucleolus dissolve. Spindle fibres start to form. Spindle fibres start to form and chromosomes move to the poles.
Metaphase 2: chromosomes move into the middle.
Anaphase 2: spindle fibres pull sister chromatids apart in towards opposite poles.
Telophase 2: nuclear envelope and nucleolus reform (and cytokineses happens) so that each cell has become two, resulting in four cells, each with half the number of chromosomes than a somatic cell.
The 'normal' amount of chromosomes is called the diploid number (in humans it is 46 chromosomes/23 pairs of chromosomes) and gametes have the haploid number of chromosomes (23 in humans).
It is important that gametes have half the genetic information so that when two gametes meet the child gets a mixture of genes from its parents and therefore is very different. This is called variation and is what has enabled evolution to happen.
Haploid cells are made in two stages: meiosis 1; and meiosis 2:
Prophase 1: chromatin condenses to form chromosomes. Homologous pairs (the same chromosomes, one from your mum and one from your dad) come together, here some segments of DNA can transfer from one into another, so alleles will swap- this is called crossing over and increases variation. Nuclear envelope and nucleolus dissolve. Spindle fibres start to form and chromosomes move to the poles.
Metaphase 1: homologous pairs line up in the middle of the cell, some of the paternal chromosomes are on the right and some on the left, the same for maternal chromosomes.
Anaphase 1: the pairs are pulled apart towards the opposite poles by spindle fibres.
Telophase1 : the nuclear envelope and nucleus reform (and cytokineses happens) so two new cells have been made. Because some of paternal and maternal DNA was in a random order, the cells have different DNA, this is called independent segregation.
Meiosis 2 happens in both of the cells formed by meiosis 1, it is the same as mitosis:
Prophase 2: nuclear envelope and nucleolus dissolve. Spindle fibres start to form. Spindle fibres start to form and chromosomes move to the poles.
Metaphase 2: chromosomes move into the middle.
Anaphase 2: spindle fibres pull sister chromatids apart in towards opposite poles.
Telophase 2: nuclear envelope and nucleolus reform (and cytokineses happens) so that each cell has become two, resulting in four cells, each with half the number of chromosomes than a somatic cell.
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| wikipedia |
Candidates should be able to analyse, interpret and evaluate data concerning early experimental work relating to the role and importance of DNA.
One experiment performed when investigating the nature of DNA was one to find out if its replication is conservative or semi conservative.
Conservative means there would be one completely new piece of DNA made and one completely old one left.
Semi-conservative means there are two pieces of DNA that are both made up of half old and half new DNA.
DNA contains nitrogen.
There are two isotopes of nitrogen 14N and 15N.
15N is heavier and 14N lighter.
If DNA contains 15N it would sink towards the bottom of a tube when centrifuged.
If DNA contains 14N it would be towards the top of a tube when centrifuged.
Scientists grew bacteria on 14N, they then removed the DNA and centrifuged it- it came out at the top of the tube, showing that the DNA of the bacteria would have in it the DNA it grew on.
Scientists then grew bacteria on 15N. This DNA came out at the bottom of the tube.
Scientists moved the bacteria from the 15N to the 14N and left them long enough that the DNA would replicate once.
They found that DNA from these bacteria came out in the middle of the tube. This was because they had one light strand, and one heavy strand. This showed that the DNA included one old strand of DNA from when it was on 14N and one new strand of DNA from when it was on 15N.
So they could conclude that DNA replicated semi-conservatively, making two strands of half-new-half-old DNA.
Conservative means there would be one completely new piece of DNA made and one completely old one left.
Semi-conservative means there are two pieces of DNA that are both made up of half old and half new DNA.
DNA contains nitrogen.
There are two isotopes of nitrogen 14N and 15N.
15N is heavier and 14N lighter.
If DNA contains 15N it would sink towards the bottom of a tube when centrifuged.
If DNA contains 14N it would be towards the top of a tube when centrifuged.
Scientists grew bacteria on 14N, they then removed the DNA and centrifuged it- it came out at the top of the tube, showing that the DNA of the bacteria would have in it the DNA it grew on.
Scientists then grew bacteria on 15N. This DNA came out at the bottom of the tube.
Scientists moved the bacteria from the 15N to the 14N and left them long enough that the DNA would replicate once.
They found that DNA from these bacteria came out in the middle of the tube. This was because they had one light strand, and one heavy strand. This showed that the DNA included one old strand of DNA from when it was on 14N and one new strand of DNA from when it was on 15N.
So they could conclude that DNA replicated semi-conservatively, making two strands of half-new-half-old DNA.
Tuesday, 25 February 2014
DNA and chromosomes resources
http://www2.le.ac.uk/departments/genetics/vgec/schoolscolleges/topics/dna-genes-chromosomes
http://getrevising.co.uk/revision-tests/dna_and_meiosis_4?game_type=flashcards#1a
http://getrevising.co.uk/revision-tests/dna_and_meiosis_4?game_type=flashcards#1a
Mitosis resources
I've decided to put up resources that I use to create posts and revise, so enjoy:
http://www.youtube.com/watch?v=LLKX_4DHE3I
http://www.cellsalive.com/mitosis.htm
http://www.youtube.com/watch?v=pOsAbTi9tHw
http://getrevising.co.uk/revision-tests/dna_and_meiosis_4?game_type=flashcards#1a
http://www.youtube.com/watch?v=LLKX_4DHE3I
http://www.cellsalive.com/mitosis.htm
http://www.youtube.com/watch?v=pOsAbTi9tHw
http://getrevising.co.uk/revision-tests/dna_and_meiosis_4?game_type=flashcards#1a
During mitosis, the parent cell divides to produce two daughter cells, each containing an exact copy of the DNA of the parent cell. Mitosis increases the cell number in this way in growth and tissue repair. Candidates should be able to name and explain the events occurring during each stage of mitosis. They should be able to recognise the stages from drawings and photographs.
We always need more cells (to replace old ones and) for growth and tissue repair.
In mitosis, one cell divides into two new cells: the first cell is the parent cell and those produced are daughter cells. The daughter cells are identical to the parent cell because they have the exact same DNA.
There are four phases in mitosis:
Prophase
DNA that was in chromatin form to condenses into chromosome form: that means it associates with proteins and winds itself into a structure. Each chromosome consists of two chromatids (identicle pairs of DNA) which are joined in the middle by centromeres.
Centrosomes move towards the poles (opposite ends) of the cell and begin to form spindle fibers (micro tubules that act like rope).
The nuclear envelope and nucleolus dissolve.
Metaphase
Chromosomes line up in the middle of the cell.
Spindle fibres which attach to the centromere of chromosomes.
Anaphase
Spindle fibres pull one half of each chromosome in each direction, at the same time the centrosomes are moving further apart towards the poles of the cell.
Telophase
Chromosomes reach poles and turn back into chromatin.
The nuclear envelope and nucleolus reform.
Prophase
DNA that was in chromatin form to condenses into chromosome form: that means it associates with proteins and winds itself into a structure. Each chromosome consists of two chromatids (identicle pairs of DNA) which are joined in the middle by centromeres.
Centrosomes move towards the poles (opposite ends) of the cell and begin to form spindle fibers (micro tubules that act like rope).
The nuclear envelope and nucleolus dissolve.
Metaphase
Chromosomes line up in the middle of the cell.
Spindle fibres which attach to the centromere of chromosomes.
Anaphase
Spindle fibres pull one half of each chromosome in each direction, at the same time the centrosomes are moving further apart towards the poles of the cell.
Telophase
Chromosomes reach poles and turn back into chromatin.
The nuclear envelope and nucleolus reform.
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| accessexelence.org |
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| biology-pictures.blogspot.com |
Candidates should be able to relate their understanding of the cell cycle to cancer and its treatment.
If there is a change in the DNA that controls the cell cycle, there can be an increase in the speed that cells grow at.
One cell with this mutation will rapidly divide into to, and this will continue to create a large group of cells, called a tumour.
These tumours are potentially disruptive to the functions of organs, as we know cancer takes many lives.
Chemotherapy is the use of chemicals to inhibit the cell cycle. They effect parts of the cell cycle for example: stopping spindle formation in the metaphase; stopping DNA replication during synthesis.
These chemicals effect the cycles of all cells in the body, but they will have a bigger effect the faster the cycle. This means that cancer cells are significantly slowed, but so are other quickly replicating cells are too, like hair cells.
One cell with this mutation will rapidly divide into to, and this will continue to create a large group of cells, called a tumour.
These tumours are potentially disruptive to the functions of organs, as we know cancer takes many lives.
Chemotherapy is the use of chemicals to inhibit the cell cycle. They effect parts of the cell cycle for example: stopping spindle formation in the metaphase; stopping DNA replication during synthesis.
These chemicals effect the cycles of all cells in the body, but they will have a bigger effect the faster the cycle. This means that cancer cells are significantly slowed, but so are other quickly replicating cells are too, like hair cells.
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