Cell Structure - All cells arise from other cells Flashcards
What is a chromosome
A DNA molecule folded into a condensed form, wrapped around histone proteins in eukaryotes
Define the term homologous chromosome
Have the same genes but may have different alleles
Define the term diploid
Cells with homologous pairs of chromosomes and is represented as 2n
Define the term haploid
Cells with one copy of each homologous pair of chromosomes and is represented by n
What are the stages of the cell cycle
- Interphase
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
What happens during interphase
- New proteins are synthesised
- DNA replicates
- New organelles are made
- Individual chromosomes are not visible at this stage
Why must DNA replication occur before cell division
SO that 2 genetically identical daughter cells are produced
What happens in metaphase
- Spindle fibres attach to the centromere of each chromosome
- The chromosomes are moved to the equator of the cell by the spindle fibres
What happens in prophase
- The nuclear membrane breaks down
- Centrioles move to the poles of the cell and make spindle fibres
- The chromosomes condense and become visible. Each chromosome is made up of 2 sister chromatids joined at the centromere
Why is mitosis important to organisms
- It allows the organism to grow
- Allows organisms to replace cells in order to repair tissues
- Results in genetically identical cells
- Asexual reproduction in some organisms
What happens in telophase
- Chromosomes have reached the poles and the spindle fibres break down
- A new nuclear membrane forms around each group of chromosomes
- The chromosomes un-condence and begin to form chromatin again
What happens in anaphase
- The centromere divides
- The spindle fibres contract, sister chromatids are pulled apart to the opposite poles of the cell
What happens in cytokinesis
The cytoplasm divides, producing 2 genetically identical daughter cells
How do you calculate mitotic index?
Mitotic index = Number of cells undergoing mitosis / Total number of cells
How to calculate the length of a certain stage of mitosis
Length of … = (Number of cells in certain stage / Total number of cells) x time of 1 cell cycle
What is cell division like in a cancer cell
- Divide uncontrollably
- Have a shorter cell cycle
- Divide more often
How do cancer treatmants prevent tumour formation
Drugs may stop
- DNA replication (disrupts interphase)
- Spindle formation / spindle contraction (prevents metaphase / anaphase)
- Cytokinesis
What are the problems with cancer treatments
These treatments do not always distinguish tumour cells from healthy cells from healthy cells, so they also kill some normal body cells that are dividing, causing side effects
How do prokaryotes divide
Binary Fission
What are the stages for prokaryotic replication
- The circular DNA and the plasmids replicate
- The copies of circular DNA move to separate poles of the cell
- The cytoplasm divides to produce 2 daughter cells
- Each cell contains a single copy of the circular DNA but a variable number of plasmids
Why do cancer treatments kill more cancer cells than healthy cells
Tumour cells divide more frequently than normal body cells
Why do viruses only infect specific host cells
Since they are unloving and acellular they do not undergo cell division
Why are viruses so difficult to treat
They replicate inside the cells where the drug is unable to bind to them
What are the stages of viral replication
- The virus attachment protein binds to a specific complementary receptor protein on a specific host cell
- The viral DNA / RNA is injected into the hist cell
- The host cell uses the viral DNA / RNA and its own ribosomes and enzymes to synthesise viral proteins
- The viral particles are formed and released from the host cell
