Lecture 1 - The Cell Flashcards
What are the types of cells
- Red blood cell
- Sperm Cell
- Muscle cell
- Nerve cell
- Photoreceptor
What does a general cell consist of
- Cell membrane - holds everything together
- Cytoplasm - everything inside cell membrane including organelles, liquid - cytosol
- Organelles
- Nucleus - largest organelle
What is the plasma membrane composed of
- Bilayer ( 2 layers ) of phospholipid molecules
- Protein molecules - protein channels - communication
- Cholestrol
- Glycocalyx
How thick is plasma membrane
5-7nm thick
Very strong - hold everything
Why is plasma membrane described as fluid mosaic
Fluid - not rigid/solid, can move/bend = structural flow
Mosaic - phospholipids scattered
What is glycocalyx
- Sugar coating around cell of body, attached to surface, - Carbohydrate
- Stick out of cell
Why do we have cholesterol in our plasma membrane?
- Maintain structural stability and fluidity of bilayer- less movement / flexibility / deformity - prevents it being hard/rigid
- If temperature too low phospholipids prevent them packing close together ( joining ) and crystalising
- If the temperature is too high, it holds phospholipids together - stops them moving - form bonds with each other
- Decreases permeability to small water soluble molecules
- Immobolizes first few hydrocarbon groups of phospholipid molecules
Name three types of integral proteins and examples of these molecules/ions
- Carrier protein
- Protein channel
- Receptor proteins
- Glucose, Sodium and Potassium
Which component of the plasma membrane is vital for restoring membrane integrity if the membrane is damaged? and explain how and why it maintains integrity.
- Phospholipid bilayer - amphipathic property…
- ## If membrane is damaged/ruptured it will automatically reform into a bilayer - hyrdophilic heads face out attracting water and hydrophobic tails face away from water repelling it - hiding inbetween, avoiding contact with water…
What are two end of phospholipids
Hydrophobic tails - non polar - repel in water - hates contact with water - lipids - face each other
Hydrophilic heads - polar - attract water - facing away from each other
What is meant by amphipathic and what does it allow in cell membrane
Molecules that are hydrophobic one end and hydrophilic other end = 2 different regions
Form bilayer = robust
What is role of glycocalyx
- Cell recognition/identity - signal to other cells in environment what that cell is - if it belongs there or not
- Adhesion – glue - sticking cells to each other and things in environment
Integral proteins
- Span membrane = act as gates/channels for molecules in and/or out = let things through
- Others can be components of receptors
- Some regions exposed to extracellular space and some to intracellular environment
Peripheral proteins
Bound to 1 face or other - anchors
What are the three types of junctions
- Mechanical junctions
- Sticky glycoproteins - glycocalyx
- Specialised cell - cell junctions
How do junctions form
Two cells come in contact with each other
Why are junctions present in cells
- Structural stability
- Share info
What are the two mechanical junctions
- Ball and socket
- Tongue and groove
Ball and socket junctions
- Movement within cells, between lens fibres
- Interlock with each other - holds it in place but still allows movement/flexibility
- Skeleton
Tongue and groove junction
- Allow side movement, not up and down
- Tongue and groove matching along entire length - tongue sticking out one side and the the groove sticks out other end
Where are tongue and groove junctions found in eye
Between cells within lens
Anchoring junctions
- Adjacent cells joined by joined by fibres from cytoskeleton
- Found in places with mechanical stress e.g. skin
- Stength, support and protection
- Proteins join together, cells can’t pull apart = anchor one cell to another
- Very robust
Gap junctions
- Directly connect cytoplasms of two different cells = molecules diffuse from one cell to the next e.g. nutrients. This is done by CONNEXONS that connect cells.
- Channels between neighboring cells that allow for the transport of ions, water, and other substances
- Involves integral proteins which fuse to each other - each protein = channel/pore. Gate opens = free movement of molecules
- Communication network between cytoplasm
- Proteins fuse between 2 joining cells = channel = cytoplasm of two cells continuous with each other
Occluding ( tight ) junction
- Adjacent protein molecules in opposing plasma membranes fuse, sealing/occluding the space between cells - prevents passage of molecules between cells
- Pull cells tight together = impermeable barrier
- Forms bond between proteins = stick together
- Seals things = prevents passage of everything esp water - dont want to lose water - otherwise cell shrivel
- Integral proteins fuse with matching proteins on cell next to it
Example of occluding junction
Between epithelial cells lining the digestive tract keep digestive enzymes and microorganisms in the intestine from leaking into the bloodstream
What are desmosomes
Anchoring junction that provide strong adhesion between cells
What are the types of desmosomes
- Belt desmosome
- Spot desmosome
- Hemidesmosome
How do desmosomes work
- Anchor cell to membrane - bound to adjacent cell
- Stop cells being pulled apart - lock together
- Inside membrane, peripheral proteins come together and form PLAQUE - bound to integral proteins = CADHERINS
What do the membrane of adjacent cells thicken into
Plaques
How are plaques anchored to inside of cell
By intermediate filaments
What are plaques of adjacent cells linked by
Cadherins
What are cadherins
Specialised adhesion proteins
Example of gap junction
- Cardiac muscle, smooth muscle: the electrical signal to contract spreads rapidly between heart muscle cells as ions pass through gap junctions, allowing the cells to contract
- Lens - nutrients by aqueous humour via gap junction as no blood vessels/supply - because dont want anything blocking it as light enters lens pupil - lens behind it. Nutrients taken up by lens on outside of lens
Why are gap junctions important
Allow rapid free movement of nutrients e.g. glucose, O2
What are connexons
- The channels formed when proteins fuse
- The junctions between membrane proteins in gap junctions
What does the cytoplasm consist of
- Cytosol
- Cytoskeleton
- Inclusions
- Membrane bound organelles
What is the cytoskeleton
Skeleton of cell composed of protein filaments scattered throughout the cytoplasm
What are the 3 type of protein filaments in the cytoskeleton
- Actin filaments
- Intermediate filaments
- Microtubules
What are actin filaments
- Thinnest and shortest
- Thin strands of actin monomers twisted in helix
- Edge of cytoplasm
- Found in muscle cells - movement
What are intermediate filaments
- Thicker than actin
- Very tough and durable - more stable and strong than others
- Prominent in places with mechanical stress
- Rapidly from and fall apart
- Takes up most of cytoskeleton
- Basket around nucleus and extends outwards
- Anchors organelles in places in cell
- Keratin - waterproof barrier
What are microtubules
- Thickest and longest
- Long tubes of tubulin proteins arranged into long tubes - twisted
- Contribute to cell shape and structure
- Facilitate movement of organelles - found in places where you want something extracellular to move around - e.g. tracheae - mucus - trap dirt, photoreceptors - evolved from cells with cilia - specilalised cilia - forms outer segment of photoreceptor - infoldings of membrane
What is an example of an inclusion
Melanin - granules, in retinal pigment epithelium - absorb excess light by photoreceptors at back of retina - brown pigment - gives iris colour and absorbs light - so only light entering eye is through pupil, not iris
What is role of cytoskeleton
- Cell shape
- Cytoplasmic movement of organelles
- Cell division by pinching inwards
- Whole cell movement
- Enzymatic reactions
- Support and movement - lengthens and shortens
How does the cytoskeleton contribute to movement and cell division
Moving nuclei to edges, changing plasma membrane shape.
Ring of cytoskeleton lengthening and pulling it together = new cell - pinches off = 2 nuclei form
Fibroblasts
- Large, flat branching support cells present in most connective tissue
- Secrete fibres e.g. collagen and some ground substance component of extracellular matrix.
- Wound healing
- Structural framework for tissues
What does a cilium consist of
9 microtubule doublets and 2 central microtubules ( move in unison, some shrink and elongate)
What is the centre of microtubule called
Centrosome
What is structure of centrosome
- Located to one side of nucleus is pair of centrioles right angles to each other
- 9 groups of microtubule triplets form wall of each centriole. Anchored onto by microtubules
- Each one can grow, break off, branch and form other microtubules
What are centrioles
Small cyndrical structure
What is role of keratin
Waterproof barrier
Where is keratin found
Hair and nails
Lysosomes
- Packaged by Golgi Apparatus
- 0.05 - 0.2 micrometres diameter
- Contains digestive enzymes - phagocytosis
What is Golgi Apparatus
- Series of flat membrane stacks associated with tiny vesicles
What is Endoplasmic Reticulum
Series of thin membrane sacs enclosing fluid cavities - cisternae
Continuous with nucleus
Smooth Endoplasmic Reticulum
- Synthesises and processes lipids, steroid hormones
- Further from nucleus
- Specialised ER
- Found in muscle - calcium storage - muscle contraction
What is function of Rough Endoplasmic Reticulum
- Folds and processes proteins made in the ribosomes
- Makes proteins for membranes of cell or parcelled into vesicles by the Golgi apparatus for subsequent export from the cell
Ribosomes
- Very small - 20-30nm
- Makes proteins for cell membranes and for export from cell
- Consists of protein and RNA
- Formed in nucleus, exit through nuclear = very small
Mitochondria
- Most abundant
- Produces energy
- ATP - aerobic respiration - glycloysis
- 0.1 - 0.2 micrometres
- Continuously reproducing division and growth
What does the nucleus consist of
- Nucleolus - makes ribosomes - rich in rNA and protein. 1 or 2 per nucleus
- Nuclear envelope - double membrane around nucleus with space between ( perinuclear cisterna )
- Nucleoplasm - jelly like fluid containing dissolved ions, nutrients and other solutes. Composed of chromatin and nucleolous suspended in matrix
- Chromatin - makes up chromosomes - contains genetic info - interwined DNA and histone proteins
- Nuclear pore - allow stuff to go in and out e.g. transcription factors
- Membrane surrounding nucleoplasm - chromatin and nuclsolous within matrix
Nucleus
- Control centre
- 5-10 micrometre diameter
- Present in most cells
- Regular shape in normal cells, irregular in cancer cells
What is structure of red blood cell
Flattened biconcave disk shape
What is function of nerve cell
Send out electrical impulses
Where does everything happen in a nerve cell
The centre
What is structure and function of muscle cell
Elongated fibre spindles
Stretch and change shape
What is function of sperm cell
Tail - swims around
What is a photoreceptor
Light detecting cell in retina
What are the different sizes of cells
- Small as 2 micrometres - in blood
- Some 30cm in length - muscle cells
- Some 1m or more - nerve cells ( neurons )
What is the size of cheek cells
20 to 60 micrometres
What is the diameter of an average cell
5 - 10 micrometres = very small
What’s different between each cell
The size, shape and function
What are the functions of the cell membrane
- Maintaining integrity of cell
- Specific regulation of passage
- Communication site
Maintaining integrity of cell membrane
- Keeping it all together
- Not generally permeable, but not a simple barrier - some things can freely move ( without energy ), other’s cant
- E.g. surfaces of epithelial cells have different permeabilities
Specific regulation of passage - cell membrane
- Specific regulation of passage of molecules inwards and outwards i.e. specific and selective gates
- e.g. protein channels - bind to specific molecules
Communication site - cell membrane
- Receptors for molecules in extracellular fluid
- E.g. hormones, neurotransmitters ( neurons communicate at synapses), drugs
- Releasing or receiving signals
- All cells work together, talk to each other, not individual unit
What is a hormone
Signalling messengers released by endocrine system
What are role of drugs in cell membrane
Influence how cells work via communication on cell membrane
How do cells in cell membrane work together
Via receptors
What would cell need without cholestrol
Cell wall
Where is cholesterol found
Hidden amongst hydrophobic tails
What is the role of membrane proteins
- Transport
- Enzymatic activity
- Receptors for signal transduction
- Intercellular joining
- Cell - cell recognition
- Attachment to cytoskeleton and extracellular matrix
Role of membrane proteins - Transport
Channel - some transport proteins hydrolyze ATP as an energy source to actively pump substances across membrane
Role of membrane proteins - Enzymatic activity
- Catalyse chemical reactions - metabolic pathway
Role of membrane proteins - Receptors for signal transduction
respond to signal - change in protein structure - delivers signal to inter cellular environment or tell extracellular environment that something is happening inside = chemical reactions
Role of membrane proteins - Intercellular joining
- Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions = cell to cell interactions
Role of membrane proteins - Cell - cell recognition
Identification tags specifically recognized by other cells - act as signals e.g gylcocalyx
Role of membrane proteins - Attachment to cytoskeleton and extracellular matrix
Stuff binding to it - helps move it around - helps maintain cell shape and fix location of certain membrane proteins
- Adheres cell to extracellular environment
What are carbohydrates on outer surface of cells attached to
Integral proteins
What are 3 examples of glycocalyx playing role in cell - cell recogniton
- Enables sperm to recognize egg cell - not wrong one as it shares nucleus - fertilization
- Signals which cells should be destroyed by phagocytosis
- Determines the ABO blood group of red blood cells
How does glycocalyx play a role in immune system
Immune cells/white blood cells - read environment, if wrong one, try to kill it
What are mechanical junctions
Change in plasma membrane which causes interlock with each other between 2 different cells
What are specialised cell - cell junctions
Protein - protein interactions between 2 different cells
Where is ball and socket used in eye
Between lens fibres
How is ball and socket used between lens fibres
- Behind cornea/pupil is the clear crystalline lens
- This disperses light onto retina, different optical powers
- When you cut it, lens is formed out of layers of cells
- Has to acommodate - so need some movement/flexibility
What are the 3 types of specialised cell - cell junctions
- Occluding (tight)
- Anchoring
- Gap
Where are anchoring junctions found with example
Found in places with mechanical stress e.g. skin
What is a belt desmisome
Goes a long way round the cell, entire circumference
What is a spot desmisome
Little ones - small area
What is a hemidesmosome
If desmosome does not link adjacent cells but only links membrane to cytoplasm
Some desmosomes don’t bind 2 cells together
Uses of hemidesmosome
- Gives internal structure - adjust shape of plasma membrane
- Everything inside ( cytoskeleton ) all connected to membrane
What is formed when peripheral proteins come together
Plaque
What is cytosol
Viscous fluid content of cell with other components suspended in it. Largely water but also sugars, salts e.t.c.
What are inclusions
- Various substances found in some cells but not others, stored nutrients, or pigments in cell
What are the two examples of inclusions
- Melanin
- Adipocytes
What are adipocytes
Fat cells in body - contain huge lipid droplets - store triglcerides as energy store
What do photoreceptors do
Absorb excess light - improves VA
Where are photoreceptros found
Back of retina
Which cells are melanin found
Melanocytes
What is diameter of actin strands
8nm
Where is actin found
Muscles and all cells - 10-30% of total cell volume
- Lining inside of plasma membrane
What is structure of actin filaments
Two strands of globular actin monomers packed into a tight helix
What is function of actin filaments
- Movement
- Mechanical support - give shape and strength to cells e,g. integral proteins
- Helps to position vesicles near membrane
How is actin filaments used in movement
Protein inside moves and contracts - turn plasma membrane into specific shape
What is exocytosis
Movement of substances out of cell
How does actin play a part in exocytosis
Helps to position vesicles near membrane
How does actin play a part in enocytosis
Movement of membrane dictated by actin
What is endocytosis
Movement of substances into cell
Where is mitochondria mostly found
Very active cells - where most energy is required
e.g. cardiac muscle, liver cell
What is meant by mitochondria being semi - autonomous
Possess some of their own DNA/genetic material which resembles that of bacteria, and they possess protein synthesis machinery for some of their own proteins
Structure of mitochondria
. 2 lipid bilayers . Smooth outer membran . Narrow intermembrane space . Inner membrane - cristae - increases SA - more proteins - energy production. Very active cells have more cristae in membrane . Matrix - jelly like
Summary of protein synthesis
The proteins we make are ‘coded’ in the DNA of our genes
The gene’s DNA is ‘transcribed’ onto mRNA
The mRNA leaves the nucleus for the cell’s cytoplasm, where it joins onto ribosomes, located on the endoplasmic reticulum.
Here proteins are made by joining together amino acids in the process of ‘translation’.
Synthesised proteins can be ‘packaged’ by the Golgi apparatus
What are the two locations of ribosomes
- Some ribosomes free in the cytoplasm producing proteins for use by the cell
- Others bound to endoplasmic reticulum – produce proteins for cell membranes and for export from the cell.
Where is RER found
- Found in cells that make protein for export e.g. plasma cells ( antibodies ), fibroblasts ( collagen , glandular cells - secrete stuff out
- Near nucleus
How is proteins used in collagen
Expressing proteins related to extracellular matrix - lots of collagen secreted from cells into extracellular environment - form network through which cells can migrate
What is function of golgi apparatus
- It modifies and packages new lipids and proteins. -
- Makes lysosomes
- Alter proteins - secreted inside of cisternae, package into vesicles, across and fuse with golgi apparatus
What are two sides of golgi apparatus
- CIS
- TRANS
Summary of two sides of golgi apparatus
cis - side facing ER - vesicles bud off ER fuse with cis face. These proteins migrate through golgi apparatus and bud off trans face - go off and fuse with cell membrane
What is role of cis side
side facing ER where vesicles from ER fuse
What is role of trans face
modified and packaged proteins leave from here for transport to other parts of cell.
What happens to proteins that are packaged into secretory vesicles
- Be released from the cell by exocytosis
- Form part of the cell membrane
- Remain in the cell for later release (lysosomes)
What is role of digestive enzymes in the lysosome
- Digest and destroy worn out components of the cell
- Useable products are recycled by diffusion into the cytoplasm
- Indigestible/insoluble products accumulate with age. These are known as LIPOFUSCIN (presence in the eye is a sign of ageing).
- Destroy bacteria and viruses
- Some cells are specialized for this type of operation – Phagocytes (macrophages)
How are these digestive enzymes from lysosomes formed
Some lysosomes dont make contact with membrane - some kept as individual packages in cytoplasm - contain enzymes - hydrolytic - packaged into lipid bubble - get rid of what you want
Pores of nucleus
There are 3000-4000 in a typical mammalian nucleus, which enable easy passage of particular substances in and out of nucleus (especially mRNA)
What is space between double membrane of nucleus
PERINUCLEAR CISTERNA
What are the types of intermediate filaments
- Epithelial and epidermal cells (hair & nails) – KERATIN - waterproof barrier
- Fibroblasts ( main cell in connective tissue) & white blood cells (mesenchymal origin) – VIMENTIN
- Striated and smooth muscle cells – DESMIN
- Astrocytes and some Schwann cells- support cells for neurone – GLIAL FIBRILLARY ACIDIC PROTEIN
