Cells Flashcards
Describe the process of DNA replication
- DNA helicase breaks the hydrogen bonds between complementary bases
- Double helix unwinds with both acting as a template strand
- Free nucleotides will attach through complementary base parings
- DNA polymerase joins the nucleotides together (on new strand) by condensation reaction forming phosphodiester bonds
- Hydrogen bonds between bases on each strand reform
- 2 daughter strands formed with each counting one old DNA strand and another newly synthesised strand = semi conservative replication
What type of replication is DNA replication and explain it ?
Semi - conservative replication - each DNA strand acts a template, daughter DNA contains one original strand and one newly synthesised strand
How do the features of DNA important in allowing semi conservative replication to occur ?
Weak hydrogen bonds = allow the two strands to separate
Two strands = both can act as template
Complementary base parings = allow for accurate replication
Explain what happens during prophase ?
- Chromosomes condense becoming more viable
- Nuclear Envelope begins to break down, nucleolus breakdown
- Centrioles move to opposite poles of cell forming spindle fibres
Explain what happens during metaphase ?
- Chromosomes line up in the equator of cell
- Spindle fibres attach to centromere and chromatid
Explain what happens during anaphase ?
- Spindle fibres contract pulling chromatids apart to opposite poles of the cell
- Centromere spilts
Explain what happens during telophase ?
- Chromosomes become long and thin = invisible
- Spindle fibres disintegrate
- Nuclear envelope and nucleolus beings to reform
Explain why when investigating mitosis you use a root tip sample ?
Where mitosis occurs
Explain why when investigating mitosis you use a stain?
Distinguish chromosomes
Explain why when investigating mitosis you squash the root tip ?
To obtain a thin sample and to allow light through sample
Why should you push down vertically above cover slip and not sideways ?
Push hard – spread / squash tissue;
Not push sideways – avoid rolling cells together /
Give ways in which a benign tumour differs from a malignant tumour ?
Doesn’t cause cancer
Does not invade other tissues causing damage
Describe ways in which both types of tumours may cause harm to the body ?
May damage organs
May cause blockages/obstructions
Mikanolide is a drug that inhibits the enzyme DNA polymerase. Explain why this drug may be effective against some types of cancer?
Prevents DNA replication so slows mitosis
New strand of DNA not formed
What is the centromere’s role in mitosis ?
Holds chromatids together
Allows chromatids move to opposite poles with centromere dividing
What is the role of centriole ?
Attachment of centromeres and chromatids;
Separation of chromatids
Describe the behaviour of chromosomes during mitosis and explain how this results in production of two genetically identical daughter cells
Chromosomes shorten
and each chromosomes contains 2 genetically identical chromatid strands
Chromosomes line up in the equator of the cell
Spindle fibres attach to centromere and chromatids
Spindle fibres contract separating sister chromatids and pulling them to opposite poles of cell
Each side receives identical genetic information
Then nuclear envelope then beings to reform around each group of chromosomes
Give a drug which prevents DNA replication and explain how ?
Mikanolide - Inhibits DNA polymerase so no new strand of DNA formed
Give a drug which prevents formation of spindle fibres and explain how ?
Vincristine which prevent mitosis as one cell will have double DNA, other with no DNA preventing the cell from dividing again
Describe what is meant by a malignant tumour
Uncontrolled cell division which leads to fast growing tumours which can spread throughout the body and metastisise to form secondary tumours
