Basic Cell Structure Flashcards
What is heterochromatin?
This is the state of chromatin that is tightly coiled, genetically inactive and dark-staining.
What is euchromatin?
The state of chromatin that is partially or fully uncoiled, genetically active and stains lightly.
How is DNA packaged?
Double stranded DNA is looped around 8 histones twice to form a nucleosome. DNA is further packaged by forming coils of nucleosomes called chromatin fibres.
What is the structure of chromatin?
DNA wraps around histone proteins forming nucleosomes (beads on a string - euchromatin). Multiple histones wrap into a 30 nm fibre consisting of nucleosome arrays in their most compact form - heterochromatin.
What is meant by the limit of resolution?
This is the minimum distance at which two objects can be distinguished.
What is the theoretical limit of resolutions for light microscopes and electron microscopes respectively?
0.2 micrometers and 0.002 nanometers
What is the function of the plasma membrane?
The plasma membrane is selectively permeable to ions and organic molecules and regulates the movement of substances in and out of the cell.
- Selective permeability
- Transport of materials along cell surface
- Endocytosis and Exocytosis
- Intercellular adhesion
- Intercellular recognition
- Signal transduction
What is the structure of the plasma membrane?
The plasma membrane is composed of a phospholipid bilayer with embedded proteins.
What is the glycocalyx?
This is a cell coat found in many cells made up of oligosaccharide and polysaccharide side chains on the outside of the plasma membrane.
What are cells stained with to show the cell coat (glycocalyx)?
Ruthenium red
What is the structure of the Rough Endoplasmic Reticulum?
This is an organelle composed of flattened sacs that fold to form cisternae. It is contiguous with the nuclear membrane and has ribosomes on the surface.
What is the function of the Rough Endoplasmic Reticulum?
It is the site of translation (protein synthesis)
What is the structure of the Smooth Endoplasmic Reticulum?
This is a tubular membranous system that is often contiguous with the Rough ER. It has no ribosomes on the surface.
Where is the Smooth Endoplasmic Reticulum abundant?
Liver, mammary glands, ovaries, testies and adrenal gland
Where is the Rough Endoplasmic Reticulum abundant?
Pancreatic secretory cells (making lots of enzymes)
What is the function of the Smooth Endoplasmic Reticulum?
Lipid synthesis, steroid synthesis and detoxification reactions
What is the structure of the Golgi Apparatus?
Stacks of flattened membranous sacs - cisternae
What is the function of the Golgi Apparatus?
Modification, sorting and packaging of proteins from the RER for secretion. Also involved in transportation of lipids and formation of lysosomes.
Which face of the golgi is nearest the nucleus?
Cis face (forming face)
Which face of the golgi is furthest from the nucleus and where secretary vesicles are formed?
Trans face
Where are lysosomes generated?
Golgi apparatus
What is a lysosome and what is it’s function?
A membrane bound organelle containing hydrolytic enzymes. It’s function is to digest cellular products, damaged organelles and pathogens brought into the cell via endocytosis.
How does Tay-Sach’s disease arise?
Tay-Sach’s disease arises from a congenital lack of lysosomal enzymes that digest components of nerve cells (glycolipids). These accumulate in the cells, causing them to swell and degenerate.
What is a peroxisome?
Peroxisomes are spherical, membrane bound structures of medium electron opacity which are abundant in cells involved in detoxification reactions.
What is the function of peroxisomes?
Peroxisomes oxidise toxic compounds such as alcohols and phenols using the enzyme catalase.
Where are peroxisomes abundant?
They are abundant in cells involved in detoxification reactions such as the liver and kidney.
What genetic disorders are caused by a lack of or reduction in the number of functional peroxisomes?
Zellweger’s Syndrome - lack of peroxisomes causes the build up of lipids in cells that are normally degraded.
Adenoleukodystrophy - an X-linked disorder
What is the structure of mitochondria?
An organelle consisting of a double membrane - the inner membrane folds to form cristae and contains enzymes for oxidation reactions of respiration.
The matrix contains many enzymes as well as the mitochondrial DNA genome.
ATP synthase can be found on inner membrane.
What is the function of mitochondria?
Site of cellular respiration, produces energy in the form of ATP.
Who is your mitochondrial DNA inherited from?
Mother
What does the cytoplasm contain?
All membrane-bound organelles, ribosomes for synthesising cytoplasmic proteins and a complex network of filaments and tubules called the cytoskeleton.
What is the cytosol?
This is the fluid portion of the cytoplasm in between the structures that contains many enzymes.
What are the 3 main types of cytoskeleton filaments?
Microtubules, actin filaments and intermediate filaments.
What is the cytoskeleton?
Network of protein filaments that gives the cell it’s shape and provides a basis for movement of the entire cell as well as internal movement of its component organelles and proteins.
What are intermediate filaments?
Strong stable structures which protects cells from mechanical stress
What are microtubules?
Tubular structures found in the cytoplasm of cells that often undergo changes - growing/retracting - by the addition or subtraction of tubulin (their building blocks).
What are centrosomes?
An example of an organisation centre for which microtubules ‘grow out’ of. This is where the spindle fibres develop from in mitosis.
What are actin filaments?
These occur as microfilaments in the cytoskeleton that can grow and retract.
What is the diameter of microtubules?
25 nanometres
What is the diameter of actin filaments (microfilaments)?
5-9nm
What is the diameter of intermediate filaments?
10 nanometres
What microtubular arrangement is often found in cilia and flagella?
9+2 arrangement
What is the nucleus?
This is the most prominent cellular organelle, containing genetic material stored in chromosomes.
What is the nucleolus?
This is a body found within the nucleus consisting of densely packed chromosomes
What is the nuclear envelope?
This is the nuclear membrane containing many different proteins that have been implicated in chromatin organisation and gene regulation
Where are Golgi abundant?
Eg cells of the salivary glands - secrete digestive enzymes
Cells of the immune system -secrete antibodies
Goblet cells - secrete mucus and mucus contains modified glycoproteins
Where are microtubules often found?
Sites where structures are moved e.g. Nerve fibres, mitosis spindle, cilia and flagella
Where are intermediate filaments often found?
Common in epithelial cells. Also found beneath inner nuclear membrane forming the nuclear lamina
How are actin filaments mainly distributed?
Cortical manner
Where are actin filaments abundant?
Beneath plasma membrane of cells for mechanical support
What is cystic fibrosis caused by?
Lack of CFTR protein on membrane, doesn’t transport chloride ions out of cells so water does not follow meaning the mucus is thick.
Which body systems are affected by cystic fibrosis?
Pancreas Respiratory tract GI tract Skin Sweat gland Reproductive system (vas deferens absent in men, in women thick mucus can block the cervix)
What effect does cystic fibrosis have on he structure and function of the CTFR protein?
It is misfiled so does not insert into the plasma membrane where it normally functions, chloride ions are therefore not pumped out of cells
Name one disease associated with defect of Golgi
Achondrogenesis - malformation of bone and cartilage
Name a disease associated with lysosomes
Tay Sachs - insufficient activity of Hexosaminidase A which breaks down gangliosides - these accumulate in brain
Name some diseases associated with peroxisomes
Zellweger syndrome and adrenoleukodystrophy
