3.2.2 all cells arise from other cells Flashcards
Uses of mitosis
- Growth in the number of cells present
- Replace dead or non-functioning cells
A sexual reproduction
binary fission
plants eg strawberry
Pros and cons of a-sexual reproduction
Pros
- only requires one organism
- can survive as a species more easily
Cons
- no variation, genetically identical, therefore change in environment could kill the whole species
What is mitosis?
- Cell division which produces 2 genetically identical daughter cells
Cell cycle
split into 3 phases
1. interphase
2. mitosis
3. cytokynesis
Interphase
The nucleus contains chromatin
Split into three phases:
- G1, growth
what is needed:
DNA helicase - break the hydrogen bonds between the 2 DNA strands
DNA polymerase
ATP
Histones
- S, synthesis
semi conservative replication of the DNA strand occurs - G2, growth2
What is needed:
more ribosomes, cytoplasm, mitochondria, soft and rough ER, golgi apparatus, lipids for membrane. For plants, chloroplasts, cellulose for cell wall, vacuole
What happens during prophase
The centrioles begin to migrate towards the poles of the cells
Chromatin shortens and thickens to become visible
Nuclear envelope disappears
What happens during metaphase
- Chromosomes line up in single file across the equator of the cell
- Centrioles produce spindle fibres which attach to the centromere protein which holds the 2 sister chromatids together in each chromosome, the spindle fibres ensures that each chromatid goes to each side
What happens during anaphase
- the spindle fibres contract causing the centromere to break
- one of each genetically identical sister chromatid is pulled to either pole of the cell
- requires energy - ATP
What happens during telophase
- The chromatically at either pole unwind they become longer and thinner and become chromatin again
- a nuclear membrane appears around them to form the nucleus
- the cell membrane folds inwards until they meet
- in plant cells the cell wall begins to form
How do prokaryotic cells replicate
Binary fission
How do viruses replicate
Inside the host cell they invade, they inject their nuclei acid into the cell to replicate the virus particles
Interphase
- cell grows
- organelles double
- DNA replicates
- longest stage in the cell cycle
Nuclear division
Either mitosis:
- Creates two identical, diploid cells
- for growth and repair
Or meiosis
- Creates four genetically different haploid cells
- creates gametes
Cytokinesis
- last stage of the cell cycle
- cytoplasm divides
Binary fission
- Before binary fission DNA is tightly coiled
- The DNA of the bacterium uncoils and replicates, if plasmids present they are also replicated
- The DNA is pulled to the separate poles of the bacterium as it increases size to prepare for splitting - membrane extends
- The growth of a new cell wall begins to seperate the bacterium
- The new cell wall fully develops resulting in the complete split of the bacterium
- The new daughter cells have tightly coiled DNA, ribosomes and plasmids
How does DNA in bacteria replicate
- circular DNA attaches to the cell membrane
- DNA helicase breaks the hydrogen bonds -
DNA nucleotides with complimentary bases sit opposite each exposed strand and form hydrogen bonds - DNA polymerase forms phosphodiester bonds
- 2 genetically identical double strands formed
Similarities between mitosis and binary fission
- 2 genetically identical daughter cells
- semi conservative replication
- DNA pulled to either pole
- DNA helicase and polymerase
Differences between mitosis and binary fission
- no chromosome structure
- no spindle fibres
- no centromeres
- no centrioles
- no nuclear envelope forms
Virus replication - lytic cycle
- virus attaches to cell
- virus injects genetic material - vRNA into the cell
- vRNA replicated inside the cell uses RNA nucleotides and enzymes
- vRNA contains information on how to synthesise the virus proteins eg. capsids, enzymes and antigens
- Virus will reconstruct itself using proteins and RNA
- Virus leaves cell using the cell membrane as a lipid envelope, so that it can fuse with cell membrane more easily, but it causes cell to burst
Virus replication - lysogenic cycle
- RNA enters the cell
- virus has enzymes called reverse transcriptase
- These enzymes construct a single vDNA strand
- From there a double vDNA strand can be formed
- This enters your nucleus and is stuck there permanently
