Please enable JavaScript.
Coggle requires JavaScript to display documents.
Topic 1: Cells Pt.2 - Coggle Diagram
Topic 1: Cells Pt.2
Stages of mitosis
Interphase:
- DNA is uncondensed (chromatin)
- DNA is replicated (S phase) to form genetically identical sister chromatids
- Cell grows in size and organelles are duplicated (G1 and G2)
Prophase:
- DNA supercoils and condenses (forms visible chromosomes)
- Nuclear membrane dissolves
- Centrosomes move to poles and begin to produce spindle fibres
Metaphase:
- Centrosome spindle fibres attach to the centromere of each chromosome
- Spindle fibres contract and move the chromosomes towards the cell centre
- Chromosomes form a line along the equator of the cell
Anaphase:
- Spindle fibres continue to contract
- Sister chromatids seperate and move to opposite side of the cell
- Sister chromatids are now regarded as two seperate chromosomes
Telophase:
- Chromosomes decondenses (DNA forms chromatin)
- Nuclear membranes form around the two identical chromosome sets
- Cytokinesis occurs concurrently
Cytokinesis:
- Cytoplasmic division occurs to divide the cell into 2 daughter cells
- Each daughter cell contains one copy of each identical sister chromatid
- Daughter cells are genetically identical
Oxygenation of Earth
The appearance of photosynthetic organisms lead to the rapidly increasing oxygenation of the earth's environment
Oceans:
- Originally, earth's oceans had high levels of dissolved iron
- Oxygen chemically reacted with the iron to form an insoluble precipitate
Rock deposition:
- Insoluble iron formed banded iron formations
- These deposits are not commonly found in rock that is younger than 1.8 billion years
Atmosphere:
- When dissolved iron was completely consumed, oxygen started accumulating in the anoxic atmosphere
Cell cycle checkpoints
A cell cycle contains numerous checkpoints that ensure the fidelity and viability of continued cell divisions
G1 checkpoint:
- Monitors potential growth conditions
- assesses level of DNA damage
G2 checkpoint:
- Monitors state of pre-mitotic cell
- identifies and repairs any DNA replication errors
-
Biogenesis
Abiogenesis requires specific conditions in order to proceed, including a reducing atmosphere and either high temperatures or electrical discharges
As these conditions no longer commonly exist on Earth, cells can only be formed from division of pre-existing cells
This law of biogenesis was demonstrated by Louis Pasteur
- Broths were stored in sealed vessels that were sterilised
- Bacertial growth occurred if vessel was unsealed, but did not occur if vessel stayed sealed
Endosymbiosis
Eukaryotic cells are believed to have evolved from aerobic prokaryotes that were engulfed by endocytosis
-
Chloroplasts and mitochondria arose via endosymbiosis:
- Membranes (have a double membrane)
- Antibiotics (show susceptibility)
- DNA ( have naked and circular DNA)
- Division (occurs via a fission-like process)
- Ribosomes (have 70S ribosomes)
Cell cycle
-
Interphase - an active phase of the cell cycle where many metabolic reactions occur:
- Consists of G1, S and G2 stages
M phase - the period of a cell cycle in which the cell and contents divide:
- consist of mitosis (P, M, A, T) and cytokinesis
Cytokinesis
Cytokinesis is the process of cytoplasm division, whereby a cell splits in 2, it occurs concurrently with telophase and differs in plants and animals
Animals:
- Microtubules form a concentric ring and contract towards the centre
Plants:
- Vesicles form at te cell centre and fuse outwards to form a cell plate
Mitotic index
-
The mitotic index will be elevated during growth and repair processes and acts as a prognostic tool for cancer
-
Cancer
Cancers are diseases caused by uncontrolled cell division resulting abnormal cell growths are called tumors
-
-
Passive transport
Simple diffusion - the net movement of particles from a region of higher concentration to a region of lower concentration until equilibrium is reached, involves small lipophilic molecules
Facilitated diffusion - the passive movement of molecules across a cell membrane via the aid of a membrane protein, involves large charged molecules
Osmolarity
-
Solutions can be measured as:
- Hypertonic: high solute concentration (gains water)
- Hypotonic: low solute concentration (loses water)
- Isotonic: Same solute concentration (no net flow)
Active transport
Active transport uses energy (ATP) to move molecules against a concentration gradient
- Molecule binds to a transmembrane protein pump
- Hydorlysis of ATP causes a conformational change, translocation the molecule across the membrane
Sometimes molecules are passively coupled to an actively transported molecule
- Symport: both molecules move the same direction
- Antiport: Molecules move in opposite directions
Vesicular transport
The fluidity of the plasma membrane allows it to break and reform around certain materials (requires ATP)
- Exocytosis: materials released from a cell via vesicles
- Endocytosis: Materials internalised within a vesicle
-
Abiogenesis
The formation of living cells from non-living materials is theorised to involve 4 key processes:
- Non-living synthesis of simple organic molecules
- Assembly of organic molecules into complex polymers
- Formation of polymers that can self-replicate
- Packaging of molecules into membranes to create an internal chemistry different from the surroundings
The miller-urey experiment replicated the conditions of a pre-biotic Earth in order to synthesize organic molecules
Mitosis
-
This process of cell cloning is needed for many important processes:
- Tissue repair
- Organism growth
- Asexual reproduction
- Development of embryos
Properties of membranes
Cell membranes have 2 key properties:
- Semi-permeable (only certain things can cross)
- Selective (membranes can regulate material passage)
-
Osmosis
The net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of higher solute concentration
Interphase
Normal metabolism cannot occur during M phase, so key events must occur during interphase to prepare for division:
- DNA replication (during S phase)
- Organelles duplication
- Cell growth
- Transcription/translation
- Obtaining nutrients
- Respiration (cellular)
Supercoiling
During mitosis, chromatin condenses via supercoiling to become tightly packed chromosomes
- due to replication (S phase), chromosomes consist of identical sister chromatids (joined at a centromere)
Cyclins
Cyclins are proteins that control progression of the cell cycle:
- Cyclins bind to cyclin dependent kinases
- The activated complex phosphorylates proteins involved in specific cell cycle events
- After the event has occured, the cyclin is degraded and the cyclin dependent kinase is rendered inactive
Cancer development
Cancers can be caused by many different factors:
Mutagens - agents that change the genetic material of cells:
- These agents may be either physical, chemical or biological in origin
- Mutagens that cause cancer are classified as carcinogens
Genetics - most cancers are caused by mutations to 2 classes of genes:
- Proto-oncogenes stimulate cell growth and proliferation
- Tumor suppressor genes repress cell cycle progression
Proto-oncogene mutations creaate cancer-causing oncogene
Cell death
The death of a cell may occur by 1 of 2 mechanisms:
Necrosis:
- The cell loses functional control due to injury, toinx, etc.
- There is a destabilization of the membranes, leading to swelling
- The cell bursts and releases it's contents
Apoptosis:
- It is a controlled event triggered by mitochondrial proteins
- Cell contents are packaged in membranous protrusions
- The cell fragments into apoptotic bodies which are recycled
Smoking
There is a strong positive correlation between the frequency of smoking and the incidence of cancer
- Cigarette smoke contains under 60 known carcinogens