Basic Cell Biology Flashcards
Describe the Nuclear envelope
- double membrane
- separates nucleus from cytoplasm
- continuous with lumen of endoplasmic reticulum
- nuclear pores (100nm)
- aid & regualte exchange of proteins
Describe histones
Proteins that aid in folding of DNA in chromosomes to tightly pack it
Describe Chromatin
- complex of histones & DNA that make up the chromosomes inside the nucleus
- 2 classes = Heterochromatin & Euchromatin
Describe Heterochromatin
- tightly condensed throughout cell cycle
- generally inactive in transcription
Describe Euchromatin
- less condensed
- contains actively transcribed genes
Describe the Nucleolus
- membraneless part of nucleus
- involved in production & assembly of ribosomes
- assembles ribosomes from >50 different proteins & 3 RNA molecules
Describe the Cytoskeleton
- cellular scaffolding contained within cytoplasm in all cells
- dynamic structure
- maintains cell shape, protects cells, enables cellular motion
What 3 filaments are found in a eukaryotic cytoskeleton ?
- microfilaments (actin)
- intermediate filaments
- microtubules
Describe Microfilaments (Actin)
- most conc. beneath cell membrane
- composed of 2 intertwined actin chains
What are the functions of microfilaments ?
- resisting tension, maintianing cellular shape
- essential for signal transduction
- important for cytokinesis, muscular contraction & cytoplasmic streaming
Describe Intermediate Filaments
- more stable than actin filaments
- heterogeneous constituents of the cytoskeleton
- throughout the cell
What are the function of intermediate filaments ?
- like actin they function in the maintenance of cell-shape by bearing tension
- organise internal 3D cell structure
- anchors organelles
- structural components of nuclear lamina
Describe the composition of intermediate filaments
- vimentins - common structural support of many cells
- keratin - found in skin, cell, hair & nails
- neurofilaments of neural cells
- lamin - giving structural support to nuclear envelope
Describe Microtubules
- made of alpha & beta tubulin, have very dynamic behaviour
- constantly elongated & shortened
- form a ring around nucleus & radiate out from this ring
- resists compression compared to other cytoskeletal filaments
What are the functions of microtubules?
- made of protofilaments
- polymers of alpha & beta tubulin dimers
- bundle in hollow cylindrical filaments 25nm diameter
- lumen is approx. 15nm in diameter
- arranged in imperfect helix
Describe centrioles
- nine triplet sets
- involved in organisation of mitotic spindle & in completion of cytokinesis
- position determines position of nucleus
Describe mitochondria
- membrane enclosed organelle
- composed of compartments that carry out specialised functions
- involved in cell signalling, cell differentiation & cell death
- inner & outer membrane
Describe the mitochondrial outer membrane
- encloses entire organelle
- contains large number of integral proteins called porins
- channels that allow molecules <5000 Da to freely diffuse across
Describe the mitochondrial intermembrane space
- same conc. of small molecules as cytosol
- freely permeable
- proteins composition differs to cytosol
- 1 protein localised to intermembrane space is cytochroeme C = part of electron transport chain
Describe the mitochondrial inner membrane
- contains proteins with 4 functions
1. those that perform redox reactions of oxidative phosphorylation
2. ATP synthase, generates ATP in matrix
3. specific transport proteins that regulate metabolite passage in & out matrix
4. No porins & highly impermeable
Describe ATP Synthase
- enzyme that synthesises ATP from ADP & inorganic phosphate
- ATP synthesis uses energy
- protons (H+) moving down an electrochemical gradient from inter-membrane space into matrix
What are Cristae?
- invaginations of inner membrane of mitochondria
- expand the SA of inner mitochondrial membrane
- enhances its ability to produce ATP
Describe the lipid presence in the inner mitochondrial membrane
- very high protein : phospholipid ratio - usually 3:1
- rich in a phospholipid called = cardiolipin
- cardiolipin contains 4 fatty acids & helps make inner membrane impermeable
Describe the mitochondrial membrane
- space enclosed by inner membrane
- contains;
- 2/3 of total protein in mitochondrion
- highly concentrated mix of hundred of enzymes
- tRNA
- special mitochondrial ribosomes
How did mitochondria arise ?
- endosymbiotic theory
- mitochondria are descended from ancient bacteria, which were engulfed by ancestors of eukaryotic cells more than a billion years ago
- we know this as mitochondria contian organelles
Describe the endoplasmic reticulum
- interconnected network of tubules, vesicles and cisternae
- cisternae = sac-like structures held together by cytoskeleton
- membrane encloses the cisternal space from cytosol
Describe the functions of the endoplasmic reticulum
- protein translation, folding & tranport of proteins for the cell membrane & transmembrane receptors
What are the 3 varieties of ER?
- Rough endoplasmic reticulum
- Smooth endoplasmic reticulum
- Sarcoplasmic reticulum
Describe the RER
- Surface is studded with ribosomes
- membrane continous with outer layer of nuclear envelope
- key in producing - lysosomal enzymes & secreted proteins
Describe the SER
Functions in other metabolic processes:
- synthesis of lipids & steroids
- metabolism of carbs
- drug detoxification
- steroid metabolism
Describe the Sarcoplasmic Reticulum
- special type of ER found in smooth & striated muscle
- contains large stores of calcium - sequesters & releases when the cell is depolarised - triggers muscle contraction
Simply describe the cell cycle
- series of temporally ordered events that leads a cell to divide itself into 2 daughter cells
What are the characteristics of the cell cycle?
- temporally ordered events
- cannot go backwards
- positive & negative feedback loops regualte function of molecules involved
- checkpoints maintain order of events in case something goes wrong
When do cell numbers change?
- growth & development
- tissue turnover
- response to injury
- physiological changes
Describe the cell cycle
- divided into 2 morphological & 4 biochemical stages
1. interphase = first gap, replication of chromosomes & second gap (G1, S, G2)
2. mitosis & cytokinesis = mitosis (M)
Describe the Mitotic (M) Phase
- division of nucleus resulting in identical complete copies of chromosomes packaged into 2 new nuclei
- mitosis is divided into 4 phases = prophase, metaphase, anaphase & telophase
Describe prophase
chromatin condenses into chromosomes
Describe metaphase
Spindle forms from microtubules & chromosomes align at the equatorial plane
Describe anaphase
sister chromatids separate
Descrobe telophase
- cell division
Give an overview of mitosis
- produces 2 daughter cells
- these daughter cells contain the exact same number of chromosomes as orginial parent cell
- daughter cells are diploid
