Cell + Tissue structure Flashcards
what is the function of the nucleus
- Largest and most important organelle
Functions : - DNA storage
- Expression/replication of DNA
- Regulates almost all functions of cell
- DNA stored complexed to protein - chromatin
- Surrounded by double membrane nuclear envelope - has nuclear pores allowing controlled transport of DNA, RNA, proteins in/out of nucleus
RBC is only cell type to lack nucleus
n.b. things move in and out of nucleus through nuclear pores
where are red blood cells made
Red blood cells are formed in the red bone marrow of bones. Stem cells in the red bone marrow are called hemocytoblasts
Inner layer of nucleus has a network of fibres called the _____ _____= it gives mechanical support to membrane - involved in DNA replication and cell division
Inner layer of nucleus has a network of fibres -** nuclear lamina** - gives mechanical support to membrane - involved in DNA replication and cell division
what is a laminopathy, give an example of some of the ones u shld be familiar with
Laminopathies (lamino- + -opathy) are a group of rare genetic disorders caused by mutations in genes encoding proteins of the nuclear lamina.
As nuclear lamina normally provides support for organising chromatin during mitosis, weakening of nuclear lamina limits ability of cell to divide
examples of laminopathy
- Hutchinson-Gilford progeria syndrome (premature aging)
- Emery-Dreifuss muscular dystrophy
what is heterochromatin
Heterochromatin
* Tightly packed/condensed DNA
Generally transcriptionally inactive - repressed
Heterochromatin is a cytologically dense material that is typically found at centromeres and telomeres. It mostly consists of repetitive DNA sequences and non-coding RNA transcripts and is relatively gene poor. Its most notable property is its ability to silence euchromatic gene expression
Inside the nucleus, heterochromatin segregates spatially from euchromatin and is localized preferentially toward the nuclear periphery and surrounding the nucleolus
what is euchromatin
Euchromatin
* More dispersed part of nucleus
* Less dense packing - open DNA unbound to protein
Composed of transcriptionally active DNA
Euchromatin is a lightly packed form of chromatin that is enriched in genes, and is often under active transcription. Euchromatin stands in contrast to heterochromatin, which is tightly packed and less accessible for transcription. 92% of the human genome is euchromatic
what is the function of ribosomes + where are they located
Ribosomes
Located either:
* Free in cytoplasm
* Bound on RER/nuclear envelope surface
- Made up of 2 subunits - 60S + 40S - complete one is 80S
- Composed of proteins and rRNA
what is the function of the golgi apparatus
the golgi apparatus is a membrane bound organelle which modifies and packages proteins for transport around the cell or into secretory vesicles to be released outside the cell
what is exocytosis + what are the 3 ways it can be done
exocytosis = process by which cells release proteins into ECM (extracellular matric) through secretory vesicles
Can be done via 3 pathways:
* Consecutive secretion - e.g. release of ECM proteins
* Regulated secretion (signal-mediated secretion) - e.g. release of hormones from endocrine cells
* Lysosomal secretion
what is a lysosome + where are they produced
Lysosomes are membrane-enclosed organelles that contain an array of enzymes capable of breaking down all types of biological polymers.
Enzymes in lysosomes can:
* Breakdown food or other organelles (autophagy)
* Breakdown invading organisms (bacteria, fungi)
* Breakdown cell itself (autolysis)
lysosomes are produced by the golgi apparatus
defects in lysosomes can cause lysosomal storage diseases, one in particular more commonly seen in people who are of Ashkenazi Jewish or French-Canadian descent is..?
Tay-Sachs disease - lysosomal storage disease- genetic disease due to failure to break down lipids - causing neuronal death in CNS
Caused by mutation in HexA gene =
- accumulation of lysosomes containing ganglioside
- destruction of neurons
- proliferation of microglia (CNS immune cells)
symptoms of Tay-Sachs
Exaggerated startle response when the baby hears loud noises.
“Cherry-red” spots in the eyes.
Loss of motor skills, including turning over, crawling and sitting up.
Muscle weakness, progressing to paralysis.
Movement problems.
Seizures.
Vision loss and blindness.
Hearing loss and deafness.
what is a ganglioside
Gangliosides are enriched in cell membrane microdomains (“lipid rafts”) and play important roles in the modulation of membrane proteins and ion channels, in cell signaling and in the communication among cells.
define endocytosis + explain the 3 types
Process by which substances/organisms can enter cells surrounded by membrane formed from internal budding off cell membrane
Its an energy-consuming process - active - requires ATP
3 types of endocytosis :
* Phagocytosis - cell eating
* Pinocytosis - cell drinking
* Receptor/clathrin-mediated endocytosis
define peroxisome
- Originate from RER
- Membrane bound vesicles containing lots of catalytic enzymes responsible mainly for breakdown of fatty acids
- Also contain catalase; enzyme needed for breakdown of H2O2 (hydrogen peroxide) - common by-product of other enzyme activity in peroxisome
- Contain important detoxifying enzymes in liver and kidney
Peroxisomal disorders - group of inherited rare metabolic diseases resulting from malfunctioning peroxisomes or their enzymes - result in H2O2 accumulation
E.g. Zellweger syndrome - absence of functional peroxisomes
symptoms:
An enlarged liver.
Characteristic facial features such as a high forehead, underdeveloped eyebrow ridges, and wide-set eyes.
Neurological abnormalities such as cognitive impairment and seizures.
what intermediate filament protein are the following structures made up of:
a) connective tissue
b) nerves
c) muscle
d) skin & epithelia
- Connective tissue - vimentin
- Nerves - neurofilaments
- Muscle - desmin
Skin & epithelia - keratin
