cells Flashcards
what do all cell types possess?
- cell membrane
- DNA
- cytoplasm
- ribosomes
what are the two subgroups within all living organisms?
prokaryotes and eukaryotes
describe prokaryotic cells
- small
- simple
- no nucleus
- bacteria and close relatives
describe eukaryotic cells
- larger
- complex
- nucleus
- in higher animals and plants
what is the function of the cell membrane?
- A semi-permeable barrier between cytoplasm and external environment
- Retains most organically produced chemicals inside the cell
- Allows a few molecules across:
diffusion, facilitated diffusion, osmosis, active transport - Communication by receptors on cell surface
what is the structure of the cell membrane?
lipid bilayer- fluid mosaic model
- phospholipid- hydrophilic polar head and hydrophobic non-polar tail
- cholesterol- inner area- prevents lysis
- proteins- gateways which allow or deny molecules in or out of the cell
what are pathologies of the cell membrane?
Hemoglobinopathies
- Sickle cell aneamia
- Thalassemia
Both hereditary and characterised by defects in haemoglobin
In addition, alterations in organisation of lipid bilayer phospholipids lead to decrease in red blood cells life span
Red blood cells are also not replaced as effectively
describe the nucleus
- Occurs ONLY in eukaryotic cells
- Location of most of the different types of nucleic acids
- DNA is largely restricted to the nucleus
- RNA is formed in the nucleus (by coding off the DNA bases) and moves out into the cytoplasm
- Nuclear envelope is a double-membrane structure – allows RNA and other chemicals to pass, but NOT DNA
- NUCLEOLUS – area where ribosomes are constructed
where is the site of transcription?
nucleus
what is the function of ribosomes?
- Occur in both prokaryotes and eukaryotes
- Eukaryotic ribosomes slightly larger than prokaryotic ribosomes
- Structure: a small and a larger sub-unit
- Main role is to facilitate protein translation
what are pathologies of the ribosome?
Ribosomopathies
- Originally thought to be fatal
- Now number of pathologies due to defects in ribosome synthesis
- Rare
Treacher Collins syndrome (TCS)
- Abnormal craniofacial development
what is the endoplasmic reticulum?
- mesh of interconnected
- involved in protein synthesis and transport
what is the function of the rough ER?
- connects to the nuclear envelope: messenger RNA converted to peptide and passed on to rough ER
Key function= Protein modification and production
Lysosomal enzymes
Secreted proteins
Integral membrane proteins
Correct folding – important for function
Appropriately ‘tagged’ for distribution throughout cell
Post-translational modifications – structure and function
what is the function of the smooth ER?
- Predominant function is manufacture of lipids
- More abundant in some cells than others and have specialised functions:
Liver – glycogen broken down to glucose
Adrenal cortex – steroid hormone production
Muscle – Ca2+ storage – sarcoplasmic reticulum. contraction of muscle cells is triggered by the orderly release of calcium ions. - also has a large roll in detoxifying a number of organic chemicals
what are dysfunctions of the ER?
- result in defective folding and processing of proteins
- role in number of neurodegenerative disorders
Alzheimer’s
Parkinson’s
Epilepsy - associated with ageing
what is the golgi apparatus?
- Only correctly folded proteins move from ER to Golgi via transport vesicles
- Proteins move from ER to Golgi via vesicles
- Golgi apparatus:
Further modifies proteins (post-translational)
Stores proteins
Packages proteins - Proteins leave Golgi in vesicles and transported to required site or exported
what are diseases related to the golgi apparatus?
- Impaired trafficking of proteins through Golgi
Defect in trafficking of protein important in making myelin (insulates nerve fibres and promotes signalling) causes hypomyelinating disorders (e.g. cataract)
- Impairments in post-translational modification capacity
Defective glycosylation disorders (glycoprotein and glycolipids)
Wide spectrum of pathologies that effect multiple organs
- Functionality lost due to mutations in proteins that make up Golgi
Muscular dystrophy
what are vacuoles?
Single-membrane organelles
Essentially part of the ‘outside’, located within the cell
Used as storage areas
Formed by fusion of numerous vesicles
what are vesicles?
- smaller than vacuoles
- transport within and to the outside of cells
what are lysosomes?
Large vesicles formed by the Golgi apparatus
Contain hydrolytic enzymes capable of destroying the cell
Lysosome contents function in the breakdown of extracellular materials
what are mitochondria?
- Contain their own DNA (mDNA) - maternal
- Thought to represent bacteria-like organisms incorporated into eukaryotic cells over 700 million years ago
- Function as sites of energy release (following glycolysis in the cytoplasm) and ATP formation: the POWERHOUSE of the cell
- Bounded by two membranes
Outer membrane is smooth and ‘sieve’ -like
Inner membrane folded into CRISTAE – surfaces on which ATP is generated (highly selective)
what are dysfunctions of mitochondria?
- Mutations in mtDNA
- Associated with (although not necessarily the cause):
Alzheimer’s Dementia
Parkinson’s disease
Huntington Disease
Diabetes
Cardiovascular disease
Stroke.
Autoimmune diseases (Sjogrens syndrome)
Cancer
what is the cytoplasm?
The material between the cell membrane and the nuclear envelope
Not static – facilitates transport of material around cell: Cytoplasmic Streaming
In eukaryotes, there are fibrous proteins in the cytoplasm known as the CYTOSKELETON:
Maintains shape of cell
Anchors organelles
Moves cell
Controls internal movement of organelles
what is the cytoskeleton?
a network of different protein fibers that provides many functions: it maintains or changes the shape of the cell; it secures some organelles in specific positions; it enables movement of cytoplasm and vesicles within the cell; and it enables the cell to move in response to stimuli.
