Unit 2 - All Cells Arise From Other Cells Flashcards
What is a chromosome?
A chromosome is 1 DNA molecule folded into a condensed form, wrapped around histone proteins in eukaryotes.
Following DNA replication what is a chromosome made from?
They’re made of 2 genetically identical sister chromatids. The chromatids are attached at the centromere.
What is the definition of homologous chromosomes?
They have the same genes, but may have different alleles.
What are diploid cells?
Cells with homologous pairs of chromosomes.
What are haploid cells?
Cells with only 1 copy of each homologous pair of chromosomes.
Example of a haploid cell?
Gamete cells.
When can cells no longer divide?
One a cell is specialised and fully differentiated it cannot divide, but unspecialised calls can divide.
What are the 3 main stages of the cell cycle?
1) Interphase
2) Mitosis
3) Cytokinesis
What is interphase?
Interphase is the time when the cell is NOT dividing. During interphase the following events take place:
-New proteins are synthesised
-DNA replicates
-New organelles are made
The individual chromosomes are not visible during interphase, instead you can see the chromatin in the nucleus.
Photo of a cell during interphase?
What is mitosis?
The process which the cell undergoes to produce 2 genetically identical daughter cells.
Why is mitosis important?
1) It allows the organism to grow.
2) Allows organisms to replace cells in order to repair tissues.
3) Results in genetically identical cells.
4) Asexual reproduction in some organisms.
What are the 4 stages of mitosis?
Prophase, Metaphase, Anaphase and Telophase.
What happens during prophase?
1) The nuclear membrane breaks down.
2) Centrioles move to the poles of the cell and make spindle fibres.
3) The chromosomes condense and become visible. Each chromosome is made up of 2 sister chromatids joined at the centromere.
Photo of a cell during prophase?
What happens during metaphase?
1) Spindle fibres attach to the centromere of each chromosome.
2) The chromosomes are moved to the equator (middle) of the cell by spindle fibres.
Photo of a cell during metaphase?
What happens during anaphase?
1) The centromere divides.
2) The spindle fibres contract, sister chromatids are pulled apart to the opposite poles of the cell.
Photo of a cell during anaphase?
What happens during telophase?
1) Chromosomes have reached the poles and the spindle fibres break down.
2) A new nuclear membrane forms around each group of chromosomes.
3) The chromosomes un-condense and begin to form chromatin again.
Photo of a cell during telophase?
What happens during cytokinesis?
The cytoplasm divides, producing 2 genetically identical daughter cells.
What is mitosis controlled by?
It is controlled by certain genes.
What leads to the formation of tumours and cancer?
If a mutation occurs in these genes, this causes uncontrolled cell division, which leads to the formation of tumours and cancer.
Characteristics of cancerous cells?
-They divide uncontrollably.
-They have a shorter cell cycle.
-They divide more often.
-They’re unspecialised and have no function.
How can tumours cause harm?
By damaging organs or blocking blood vessels to organs.
How do cancer treatments work?
They mainly work by targeting parts of the cell cycle to prevent the cell from dividing. For example, these drugs may stop:
-DNA replication (disrupts interphase)
-Spindle formation/spindle contraction (prevents metaphase/anaphase)
-Cytokinesis
What’s a side effect of cancer treatments?
They do not always distinguish tumour cells from healthy cells, so they also kill some normal body cells that are dividing, causing side effects.
Why do treatments target tumour cells more?
Because tumour cells divide more frequently than normal cells.
What is the process called that prokaryotic cells replicate by?
Binary fission.
What are the steps of binary fission?
1) The circular DNA and the plasmids replicate.
2) The copies of circular DNA move to separate poles of the cell.
3) The cytoplasm divides to produce 2 daughter cells.
4) Each cell contains a single copy of the circular DNA but a variable number of plasmids.
Why do viruses use a specific host cell to replicate?
Because viruses are non-living and acellular, so they don’t undergo cell division.
How do viruses replicate?
1) The virus attachment proteins binds to a specific complementary receptor protein on a specific host cell.
2) The viral DNA/RNA is injected into the host cell.
3) The host cell uses the viral DNA/RNA and its own ribosomes and enzymes to synthesise viral proteins.
4) The viral particles are formed and released from the host cell.
Why are viruses hard to treat with drugs?
They’re hard to treat with drugs because they replicate inside the cells where the drug is unable to bind them.
How do calculate the length of a certain stage of mitosis?
(Number of cells in certain stage divided by total number of cells) multiplied by 100.
What is the formula for mitotic index?
Number of cells undergoing mitosis (visible chromosomes) divided by total number of cells. Always give your mitotic index answer as a decimal. ONLY convert it to a percentage of the question asks you to!
