Topic 1 - Cells Flashcards
what are the functions of life?
- Metabolism
- Reproduction
- Sensitivity
- Homeostasis
- Excretion
- Nutrition
- Growth
prokaryotic DNA is…
DNA is naked
DNA is circular
Usually no introns
eukaryotic DNA is…
DNA bound to protein
DNA is linear
Usually contains introns
prokaryotic organelles have…
No nucleus
70S ribosomes
eukaryotic organelles have…
Has a nucleus
80S ribosomes
prokaryotic reproduction happens…
Via binary fission
Single chromosome
eukaryotic reproduction happens…
Via mitosis and meiosis
Paired chromosomes
structure of a phospholipid
- Contain a polar (hydrophilic) head composed of phosphate (+ glycerol).
- Contain two non-polar (hydrophobic) tails, each composed of a fatty acid chain.
- Hence, phospholipids are amphipathic (have hydrophilic and hydrophobic parts)
Arrangement in Membranes
- Phospholipids spontaneously arrange into a bilayer.
- The hydrophilic phosphate heads face out into the surrounding solution, while
the hydrophobic fatty acid tails face inwards and are shielded from the polar fluids.
Properties of the Phospholipid Bilayer
The bilayer is held together by weak hydrophobic interactions between the tails.
- Individual phospholipids can move within the bilayer (fluidity and flexibility).
- Amphipathic properties restrict passage of certain substances (semi-permeable).
Cholesterol is…
- a fundamental component of animal cell membranes
- It is not present in plant cell membranes (as they have a rigid cell wall)
- Cholesterol reduces membrane fluidity and permeability to some solutes
- It also anchors certain peripheral proteins and prevents crystallization
- amphipathic
Types of Membrane Transport
- Passive (along concentration gradient, no ATP expenditure)
- Active (against concentration gradient, ATP is required)
Passive Transport is…
The net movement of particles from a region of higher
concentration to a region of lower concentration
Active Transport is…
Active transport uses energy (ATP) to move molecules
against a concentration gradient (i.e. from low to high)
Vesicular Transport is…
The fluidity of the plasma membrane allows it to break and
reform around certain materials (this process requires ATP)
Exocytosis:
Materials released from a cell via vesicles
Endocytosis:
Materials internalised within a vesicle
Osmosis is…
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
Osmolarity is…
Osmolarity is a measure of solute concentration
Solutions can be measured as…
Hypertonic
Hypotonic
Isotonic
Hypertonic is…
High solute concentration (gains water)
Hypotonic is…
Low solute concentration (loses water)
Isotonic is…
Same solute concentration (no net flow)
what is Abiogenesis?
The formation of living cells from non-living materials
(abiogenesis) is theorised to involve 4 four key processes
what are the 4 key processes of abiogenesis?
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
Biogenesis…
Abiogenesis requires specific conditions in order to proceed
• Including a reducing atmosphere (no oxygen) and either
high temperatures (>100oC) or electrical discharges
explain the Biogenesis law and who demonstrated it…
This law of biogenesis was demonstrated by Louis Pasteur
• Broths were stored in sealed vessels that were sterilised
• Bacterial growth occurred if vessel was unsealed, but
did not occur if vessel stayed sealed (no contamination)
Endosymbiosis is…
the theory that Eukaryotic cells are believed to have evolved from aerobic
prokaryotes that were engulfed by endocytosis
The engulfed cell remained undigested and contributed new
functionality to the engulfing cell (i.e. it became an organelle)
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)
state the 2 phases on the Cell cycle
Interphase and M phase
what is Interphase?
An active phase of the cell cycle where many metabolic reactions occur
• Consists of G1, S and G2 stages
What is M phase?
The period of a cell cycle in which the cell and contents divide
• Consists of mitosis (P, M, A, T) and cytokinesis
Interphase cannot….
cannot occur during M phase, so key events must occur during interphase to prepare for division: • DNA replication (during S phase) • Organelle duplication • Cell growth • Transcription / translation • Obtaining nutrients • Respiration (cellular)
what is 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)
what is Mitosis?
Mitosis is the division of a diploid nucleus
into two genetically identical diploid nuclei
This process of cell cloning is needed for
many important processes:
• Tissue repair
• Organism growth
• Asexual reproduction
• Development of embryos
what is Cytokinesis?
Cytokinesis is the process of cytoplasm division, whereby a cell splits in two
• It occurs concurrently with telophase and differs in plants and animals
Animals:
• Microtubules form a concentric ring and
contract towards the centre (centripetal)
Plants:
• Vesicles form at the cell centre and fuse
outwards to form a cell plate (centrifugal)
what is the Mitotic Index formula?
Cells in mitosis*
_______________ = Mitotic Index
Total number of cells
state the phases of mitosis in order
prophase, metaphase, anaphase telophase
what happens in 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)
what happens in Prophase?
DNA supercoils and condenses (forms visible chromosomes) • Nuclear membrane dissolves • Centrosomes move to poles and begin to produce spindle fibres
what happens in 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 (middle) of the cell
what happens in Anaphase?
Spindle fibres continue to contract • Sister chromatids separate and move to opposite sides of the cell • Sister chromatids are now regarded as two separate chromosomes
what happens in Telophase?
Chromosomes decondense (DNA forms chromatin) • Nuclear membranes form around the two identical chromosome sets • Cytokinesis occurs concurrently
what happens in Cytokinesis?
Cytoplasmic division occurs to divide
the cell into two daughter cells
• Each daughter cell contains one copy
of each identical sister chromatid
what are Cell Cycle Checkpoints?
A cell cycle contains numerous checkpoints that ensure
the fidelity and viability of continued cell divisions
what happens in checkpoint G1?
Monitors potential growth conditions (nutrients, etc.)
• Assesses level of DNA damage (from UV, etc.)
what happens in checkpoint G2?
Monitors state of pre-mitotic cell (suitable size, etc.)
• Identifies and repairs any DNA replication errors
role of Metaphase checkpoint
Ensures proper alignment (prevents aneuploidy)
what are Cyclins?
Cyclins are proteins that control progression of the cell cycle
The activated complex phosphorylates proteins involved
in specific cell cycle events (e.g. centrosome duplication)
• After the event has occurred, the cyclin is degraded and
the cyclin dependent kinase is rendered inactive
how is cancer caused?
Cancers are diseases caused by uncontrolled cell division
• The resulting abnormal cell growths are called tumors
Tumor cells may remain in their original location (benign)
or spread and invade neighboring tissues (malignant)
state the 2 ways of how a cell may die:
Necrosis and Apoptosis
what is Necrosis?
(uncontrolled ‘cell homicide’)
• The cell loses functional control due to injury, toxins, etc.
• There is a destabilization of the membranes, leading to swelling
• The cell bursts and releases its contents (causing inflammation)
what is Apoptosis?
(programmed ‘cell suicide’)
• It is a controlled event triggered by mitochondrial proteins
• Cell contents are packaged in membranous protrusions (blebs)
• The cell fragments into apoptotic bodies which are recycled
