Cell Division Flashcards
What is an Exon?
Regions od DNA that code for proteins
What are the regions between Exons called?
Introns = Non-coding DNA called introns (interruptions)
What are introns?
They contain repeated blocks of nucleotides
What is the function of introns?
The number of times these blocks are repeated produces the genetic variation we see in finger prints.
Do Eukaryotic genes have introns? What does this mean if reference to the type of gene they have?
Yes they have introns which creates discontinuous genes
Do Prokaryotic genes have introns? What does this mean if reference to the type of gene they have?
No they do not have introns which means that have continuous genes
What are the three steps to DNA splicing?
- A gene composed of exons and introns is transcribed to RNA by RNA polymerase.
- Processing involves ribozymes and proteins in the nucleus to remove the intron-derived RNA and splice together the Exon- derived RNA into mRNA.
- After further modification the mRNA travels to the cytoplasm, where is directs protein synthesis.
What is the function of the nucleus?
The nucleus contains the DNA, which carries instructions for the cell-metabolism, enzymes etc.
What is the function of the nucleolus?
Copies instructions from DNA into mRNA. Ribosomes manufacture
What is the function of ribosomes?
They are either attached to the endoplasmic reticulum or free in the cytoplasm. Decodes the instruction contained in the mRNA
What is the function of the Rough Endoplasmic Reticulum?
Protein synthesis on RER and transport of newly made proteins through the cell
What is the function of the Golgi body?
Process and package proteins
What is the function of vesicles?
Transport materials from the ER to the Golgi body to the cell surface membrane or other sites in the cell.
What is the cell in for the majority of the cell cycle?
Interphase
What occurs during interphase G1?
Protein synthesis, cytoplasm and the number of organelles increase rapidly, mitochondria and chloroplasts also replicate
What occurs during the synthesis phase of mitosis?
DNA replicates (amount of DNA doubles)
What occurs during the G2 phase of mitosis?
The proteins necessary for cell division are synthesised, ATP synthesis increases
What happens during the INTERPHASE phase of a cell?
.DNA replication occurs .The cell grows in size .Carries out normal cell activities .Replicates organelles .Replicates mitochondria and chloroplasts
Define mitosis?
Division of one nuclei into two genetically identical ones
What type of division in mitosis?
Nuclear division
What is the product of mitosis?
Two genetically identical daughter nuclei, each containing the same number of chromosomes
When is mitosis used? (4)
- a-sexual reproduction
- growth
- repair of damaged tissue
- cell replacement of old or damaged cells
Where does mitosis occur?
In all the somatic body cells
What are the four stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What occurs to the DNA during PROPHASE of mitosis?
.DNA has already replicated
.Chromatin condenses (shortens and thickens) and becomes visible as long threads called chromosomes.
.Each chromosome is made of two genetically identical chromatids held together by a centromere.
What happens during PROPHASE of mitosis after the chromatin has condensed?
.The centrioles move to opposite sides of the nucleus
.The centrioles develop the spindle apparatus
What happens to the nucleolus and nuclear membrane during PROPHASE of mitosis?
.Nucleolus breaks down and disappears
.The nuclear membrane begins to break down
What happens during the METAPHASE of mitosis?
.The nuclear membrane has disappeared
.The microtubules attach to the centromere and cause the chromosomes to arrange on the equator of the spindle
What happens during the ANAPHASE of mitosis?
.The attached microtubules contract which splits the centromeres in two and pulls chromatids to opposite poles of the cell
.Chromatids are now called daughter chromosomes
What happens during the TELOPHASE of mitosis?
.The daughter chromosomes reach the poles and uncoil and lengthen
.Spindle fibres disintegrate
.Nucleolus and nuclear envelope re-form
.In animal cells, cytokenesis occurs
.In plants cells a cell plate and cell wall forms across the equator
What is the equation to calculate mitotic index?
(Number of cells in mitosis/ Total number of cells) X100
What is cancer and how does it occur?
.Cancer is caused by uncontrolled mitosis
.Cancerous cells divide repeatedly with the formation of a tumour (an irregular mass of cells)
.Cancers are thought to be initiated by gene mutations in either oncogenes or tumour suppressor genes, which control cell division.
What are the three moments genetic variation can occur?
- During crossing over, parts of homologous chromosomes may be exchanged producing new allele combinations
- During independent assortment of homologous chromosomes, maternal and paternal chromosomes are mixed up
- During sexual reproduction, there is random fusion of haploid gametes to form the zygote
What are the 6 key differences between mitosis and meiosis?
- Meiosis has two divisions resulting in four daughter cells where as mitosis has one division resulting in two daughter cells
- Meiosis halves the number of chromosomes, in mitosis it remains uncharged
- In meiosis the daughter cells are genetically different, it mitosis they are genetically identical
- In meiosis homologous chromosomes pair up, in mitosis they are not associated in pairs.
- In meiosis crossing over occurs and chiasmata form, in mitosis no crossing over occurs
- Meiosis produces variation, mitosis does not
What is the product of meiosis?
Cells containing one set of chromosomes (one from each homologous pair)
When does meiosis occur?
Sexual reproduction, 1 diploid cell divides to produce 4 haploid cells (gametes)
What is the only difference INTERPHASE 1 and interphase in mitosis?
Each homologous pair of chromosomes come together (synapsis) to form a bivalent
What occurs in late PROPHASE I in meiosis?
.Each chromosome in a bivalent has two chromatids
.Crossing over takes place between the non-sister chromatids in the bivalent
.Each chromatid may break and reconnect to another chromatid
.The point of crossing over is called a chiasma
.This process results in recombination of maternal and paternal genetic information
What occurs in METAPHASE I in meiosis?
.The spindle fibre attach to the centromere and move the whole chromosome to the equator of the cell
.The bivalents arrange themselves at the equator of the spindle
.Homologous chromosomes arrange themselves randomly at the equator of the cell (random assortment of homologous chromosomes) leading to genetic variation.
What occurs in ANAPHASE I in meiosis?
.The spindle fibres attached to the centromere of each homologous chromosomes shorten to pull them to opposite poles of the cell
.Whole chromosomes are pulled
What occurs TELOPHASE I in meiosis?
.The organelles, cytoplasm and membranes become evenly distributed in two new cells: cytokenisis.
.Each cell now contains half the number of original chromosomes (still made of two chromatids)
.The chromosomes are genetically different from those in the original cell
.Two new nuclear envelopes reform (animal cells)
Describe PROPHASE II of meiosis?
.Chromatin condenses and chromosomes are visible
.Centrioles replicate
.A new spindle reforms at right angles to the first
.Nuclear envelope and nucleolus disappears
Describe METAPHASE II of meiosis?
.The chromosomes align themselves randomly on the equator of the spindle
.Each chromosome is made up of a pair of chromatids
.The phase again introduces genetic variation due to the random assortment of chromatids at the equator.
