Cell biology Flashcards
How is DNA stored in the nucleus?
Chromatin, DNA + Histones
Where does transcription occure?
Nucleus
What is the nuclear envelope compose of?
2 lipid bilayer membranes which surround the nucleus
What does each membrane layer of the nuclear envelope produce?
Inner layer- Nuclear lamina
Outer membrane- Continuous with the endoplasmic reticulum
What is heterochromatin?
Tightly packed form of DNA
Consists of genetically inactive sequences and many Gene’s are repressed
What is euchromatin?
Tightly packed form of chromatin
often under active transcription
92% of human genome is euchromatin
What is the location and function of the nucleolus?
sits in the nucleus
Makes rNA
Made of proteins, DNA, RNA
What is the nuclear pore? What is its function?
Protein complexes found on the nuclear envelope
Allows the transport of molecules across nuclear membrane:
e.g,
mRNA and ribosomal proteins to the cytoplasm
carbohydrates, signaling molecules and lipids into the nucleus.
What causes laminopathies?
When nuclear lamina is defective, Heterochromatin’, can be transcribed (usually inactive)
Give examples of laminopathies
muscular dystrophy and Progeria syndrome.
Describe the condition Progeria syndrome.
Premature ageing
Nuclear lamina is weakened
This limits the ability of the cell to divide.
What is the function of the rough ER and its ribosomes?
(Protein production)
Translates RNA into protein.
Labelles and sorts proteins
Foldes and modifies proteins
Synthesize proteins from amino acids to make peptides, then polypeptides and complete proteins.
Glycosylates proetins
Which conditions are caused by protein misfolding?
Cystic fibrosis,Type 1 diabetes, Alzheimer’s disease
What is the function of the smooth ER?
- Responsible for the synthesis and breakdown of lipids, synthesis of carbohydrates,
- Acts as a store for calcium.
Which conditions are caused by Disorder of smooth ER?
obesity & jaundice.
What is the function of the Golgi apparatus?
Stack of membranes that package and modify proteins from the rough ER into membrane bound vesicles
What is glycosylation? Where does it occure?
Attachment of sugar monomers to proteins.
Occurs in the Rough ER and golgi apparatus
what is the function of the plasma membrane?
Anchores the skeleton
Allows constant exchange of molecules between the cell and its surrounding
Why is the plasma membrane described as a fluid mosaic?
Lipid molecules in the membrane are very mobile and constantly moving past one another
What effect can receptors on the plasma cell membrane have on the nucleus?
They can signal changes in gene expression
What is exocytosis?
Form of active transport as energy is required
Contents of a cell is released into the exterior through fusing with the cell membrane
How do cells insert membrane proteins, ions channels , receptors and lipids onto the cell membrane?
Exocytosis
What are the two types of exocytosis?
1) Ca2+ triggered non-constitutive (i.e., regulated exocytosis)
2) non-Ca2+ triggered constitutive (i.e., non-regulated).
What is the difference between non-constitutive and constitutive exocytosis?
Constitutive- carried out by all cells and transfers molecules from the Golgi network to the outer surface of the cell
N
on-constitutive (regulated)- occurs in response to specific conditions (clathrine coat), signals or biochemical triggers, and is the process underlying the release of cytokines, hormones, neurotransmitters and other small signalling molecules
What is endocytosis?
cell transports molecules (such as proteins) into the cell from the plasma membrane by engulfing them in an energy-using process.
The engulfed components are either broken down to simple components and recycled back to the surface or targeted for degradation by lysosomes
What are lysosomes? What is there function?
vacuoles containing hydrolytic enzymes that break down biological material into its constituent parts to provide food for the cell
They can also fuse with phagocytes to digest material such as bacteria
So they:
Defense against disease.
Autophagy – clean up of organelles
Autolysis after cell death
What is Lysosomal Storage Diseases?
A group of 50 rare inherited metabolic disorders.
Characterized by an abnormal build-up of various toxic materials in the body’s cells as a result of lysosomal enzyme deficiencies.
1 in 5000 live births
Life expectancy 15 years.
Give an example of a Lysosomal Storage Diseases?
Tay Sachs disease
What is the function of Peroxisome? Where does it originate from?
It breaks down very long chain fatty acids through beta-oxidation
Originates from the rough ER and contain 50 different enzymes
What is the function of catalse?
An enzyme produced by peroxidase which breaks down the toxic hydrogen peroxide into water
What are peroxisomes?
Sites of synthesis of several enzymes found in the liver and kidney
Those in the liver produce bile
What produces bile in the liver?
Peroxisomes
What is Peroxisome biogenesis disorder?
autosomal recessive developmental brain disorders that also result in skeletal and craniofacial dysmorphism, liver dysfunction, progressive sensorineural hearing loss, and retinopathy
What are mitochondria?
organelles which take in nutrients, breaks them down, and oxidises them into ATP.
How does the mitochondria initiate cell death?
Pores are formed in the inner mitochondrial membrane due to cellular damage.
Then the mitochondria releases cytochrome C to starts the apoptotic cascade
What are Mitochondrial diseases, give examples
Present themselves as neurological disorders
e.g. Parkinson disease, cardiac dysfunction, heart failure and autism
How does the mitochondria contribute to aging?
Leakage of the high-energy electrons in the respiratory chain with time forming reactive oxygen species. Oxidative stress leads to mitochondrial DNA mutation.
What is the cytoskeleton?
network of three types of proteins:
1. Microfilaments (formed from actin);
- Intermediate filaments ( fibrous proteins with similar properties)
- Microtubules (formed from the tubulin).
Each filament associates with proteins to conduct function
They are responsible for the cells change in shape, position, and movement.
Describe the structure and function of actin microfilaments
Thinest filament protein
Organised into bundles
Cores of actin filaments are bound by villin protein.
They support finger like projections of the cell membrane (filopodia and microvilli)
F-Actin and myosin cross-bridges in non-muscle cells supply the motile force involved in cell division, cell movement and the uptake of external material by cells (endocytosis).
What do genetic diseases of actin microfilaments result in?
congenital hearing loss and skeletal and cardiac myopathies
Describe the structure and function of Intermediate filaments
Provide strength
highly-tensile, yet flexible cables, that penetrate the entire cell.
Found in durable structures like hair, fingernails
10 mmin diameter
Name of Intermediate filaments found in the nucleus, connective tissue, muscle cells nerve cells and skin
Nucelus- Lamins Connective tissue- Vimentin Nerve tissue-Neurofilaments Muscle tissue- desmins Epethilal tissue- Keratins
Consequence of mutations in keratin?
weaken skin causing blistering with the slightest contact from birth
Describe the structure and function of Microtubules
20-25nm in diameter.
Hollow tube made from tubulin
Help to produce movment in flagella and cilia using dynein which links adjacent microtubules and allows the to side over each other
also form the framework of the mitotic spindle during chromosomes division.
