Module 2.6 Flashcards
Cell division, diversity and differentiation (38 cards)
Phases of the cell cycle
Interphase, prophase, metaphase, anaphase, telophase, cytokinesis
What happens in interphase
G1 - growth phase
organelles duplicate, synthesis of products needed e.g. enzymes for DNA replication
S - synthesis phase
DNA replicates creating 2 sister chromatids held together by a centromere
G2 - growth phase
cell grows
What is mitosis
The division of the nucleus to produce 2 genetically identical daughter cells
What happens in cytokinesis
After mitosis or meiosis the cytoplasm and plasma membrane pinch inwards to separate the 2 nuclei into 2 separate cells
How is the cell cycle regulated
Checkpoints
Checks all DNA and organelles are replicated before mitosis
Prevents uncontrolled division
Detect and repair damage to DNA
Ensure DNA is only replicated once
Mitosis - prophase
Chromosomes condense and supercoil
Nuclear envelope breaks down
Centriole replicates and move to oppositive poles
Spindle forms
Mitosis - metaphase
sister chromatids line up along the equator of the spindle
Joined to the spindle by the centromere
Mitosis - anaphase
Centromere of each sister chromatid splits
Motor proteins pull the chromosomes of a homologous pair apart by the centromere along the spindle dragging the separate chromatids to opposite poles
Mitosis - telophase
Separated chromosomes reach the poles
Nuclear envelope forms around the set of chromosomes at each pole
cell now contains 2 genetically identical nuclei
significance of mitosis
Growth
Tissue repair
Asexual reproduction in plants, animals and fungi
What is meiosis
Production of 4 haploid cells with genetic variation
Meiosis - Prophase 1
chromosomes condense and supercoil
Nuclear envelope breaks down
Centriole replicates and move to oppositive poles
Spindle forms
2 sets of sister chromatids come together in homologous pairs
Crossing over - non-sister chromatids wrap around each other and swap sections to shuffle alleles
Meiosis - Metaphase 1
Homologous pairs line up along the equator of the spindle
Joined to the spindle by the centromere
Independent assortment - homologous pairs are arranged randomly facing opposite poles of the cell determining how they separate
Meiosis - anaphase 1
Motor proteins pull the chromosomes (containing 2 non-identical chromatids) of a homologous pair apart along the spindle
What are sister chromatids
After DNA replication 2 their are 2 genetically identical chromatids joined at the centromere
What is a homologous pair
2 sets of sister chromatids that contain the same types of genes but are genetically different as one is maternal and one is paternal
Meiosis - telophase 1
New nuclear envelopes develop
Each new nucleus contains half the number of original chromosomes but each chromosome has 2 chromatids
Meiosis - Prophase 2
Nuclear envelopes break down
Centrioles replicate and move to poles
Spindles form at a right angle to the previous spindle
Chromatids of each chromosome are no longer identical because of crossing over
Meiosis - metaphase 2
Chromosomes attach by the centromere to the spindle equator
Independent assortment - chromatids of each chromosomes is arranged randomly determining the separation
Meiosis - Anaphase 2
Centromeres divide
Chromatids are pulled apart by motor proteins towards opposite poles
Meiosis - telophase 2
Nuclear envelope form around the 4 haploid nuclei
How meiosis produces genetic variation
Crossing over in prophase 1 shuffles alleles
Independent assortment of chromosomes in anaphase 1 randomly distribute maternal and paternal chromosomes of each homologous pairs
Independent assortment of chromatids in anaphase 2 leads to random distribution of chromatids from the pair of chromatids
How are erythrocytes specialised
No nucleus mitochondria or ER little cytoplasm - more space for haemoglobin
Biconcave disc - more surface area for oxygen and co2 diffusion
flexible - fit through capillaries
small - fit through capillaries
