Cell biology Theme 1 Flashcards
All cells need to
Reproduce , Grow , Release energy , excrete waste, move and respond to the environment
The main 2 types of cells are
prokaryotic and Eukaryotic
The 2 distinct features of eukaryotic cells are
A nucleus and membrane bound organelles
The nuclear envelope is continuous with the …
Endoplasmic reticulum
What is the nuclear lamina ?
A fibrous network of filamentous proteins that provides mechanical support
What are the function of nuclear pores ?
To communicate with the cytosol
What is the nucleolus ?
A dense sphere in the nucleus where rRNA is formed
What is the endoplasmic reticulum ?
A irregular maze of interconnected sacs that are membrane bound
What is the function of the endoplasmic reticulum ?
Synthesis of many cellular components as well as secretion
What is the function of the RER ?
Has ribosomes on its surface which are forced to attach if the gene has an ER signal sequence
What is the function of the SER ?
The site of lipid synthesis and protein modification (eg. formation of glycoproteins)
What is the golgi apparatus ?
Sacks of flattened, membrane enclosed sacs called citsternae which collectively make the golgi.
What is the function of the golgi apparatus ?
Modifies and packages molecules made in the ER destined fro secretion/transportation. Usually proteins and lipids.
How are molecules transported by golgi ?
They are transported from the cis to trans end of the apparatus , then to lysosomes,endosomes or secretory vesicles.
What is the endomembrane system ?
A continual exchange of materials takes place between the endoplasmic reticulum , golgi apparatus , lysosomes and outside of the cell
How can molecules be modified ?
Glycolisation- the attatchment of a branched oligosaccharide to lipid/protein.
What is the function of glycoproteins ?
intercellular signaling, receptors and membrane integrity
What is the function of a lysosome ?
intracellular digestion , they release nutrients from ingested food. They also contain hydrolytic enzymes that are active under a low pH.
How do lysosomes maintain a low pH?
There is a proton pump that actively tansports H+ ions into the lysosome.
What are peroxisomes ?
A small organelle present in the cytoplasm that contains the reducing enzyme catalase
What is the function of mitochondria ?
Generates chemical energy for the cell through ATP production in respiration
What is the membrane of the mitochondria like ?
Double membrane , the inner membrane is folded to form cristae
What is the difference between the cytoplasm and the cytosol ?
The cytoplasm is the contents of the cell including the organelles whilst the cytosol is the water based gel where fundamental chemical reactions take place.
What is the function of the plasma membrane ?
it maintains cell integrity , allows selective passage and has cell surface receptors
What is the principle of compartmentalisation and why is it useful ?
the formation of cellular compartments by membrane enclosed regions. Usually needed for isolation, efficiency and economy. Allows the separation of anabolism and catabolism
Why is compartmentalisation needed in mitochondria ?
Provide additional surface area , allows non-compatible reactions to occur at the same time
Why is compartmentalisation needed in lysosomes ?
allows the maintenance of an acidic environment and to prevent auto-digestion of organelles.
What is endocytosis ?
The process by which a substance is captured from the outside of the cell. Engulfing it with the cell membrane , bringing it into the cell
What are the 2 types of endocytosis ?
Phagocytosis and pinocytosis
What is the process of Phagocytosis ?
A particle binds to the phagocytic cell surface and activates a receptor. This causes sheet like projections called pseudopods to engulf the bacteria into a phagosome. The phagosome binds with a lysosome and the bacteria is destroyed.
What is pinocytosis ?
Ingestion of fluid and small molecules via small pinocytic vesicles. A droplet becomes adsorbed on the cell surface and the membrane invaginates to form a vesicle in the cytoplasm.
What are pinocytic vesicles coated in ?
Clathrin
The bilayer arrangement is ?
the most energetically favourable
the fluidity of the lipid bilayer depends on ?
composition - ie. the nature of the phospholipid tails, the closer and more regular the packing of the tails the more viscous and less fluid the membrane
The shorter the chain length…
the smaller the tendency of tails to interact and the more fluid the bilayer is
What is cholesterol and what is its function ?
Short and rigid molecules that fill spaces and kinks created by unsaturated tails . It stiffens the bilayer making it less permeable and less fluid.
Why is membrane fluidity important ?
Permits lipids and proteins to diffuse from sites of synthesis to other regions. Allows molecules to distribute evenly between daughter cells.
What is the cytoskeleton ?
A structure that helps cells maintain their shape and allows internal organisation
The cytoskeleton is made of which 3 types of protein ?
Actin , Microtubules and Intermerdiate filaments
What is the structure of intermediate filaments ?
Rope like strands made of helicous fibrous proteins , they are the toughest
What is the role of intermediate filaments ?
they are the toughest filament and provide mechanical strength
Describe the role of Keratin
It is concentrated and anchored at the plasma membrane of cell-cell junctions in cells prone to mechanical strength
What are the 2 types of intermediate filaments ?
Cytoplasmic and Nuclear
Describe the properties of nuclear and cytoplasmic filaments
Cytoplasmic are rope like whilst nuclear are meshwork like
What are microtubules made of ?
tubulin - alpha and beta
What are the structure of microtubules ?
Heterodimers , hollow cylinders which grow from centromeres. the heterodimers add to the positive end opposite the negatively charged centromere
What is the function of microtubules ?
They have a role in transportation and positioning organelles. They act as tracks.
How do microtubules play an important role in cell division ?
Microtubules guide chromosomes to daughter cells during mitosis
How do Antimitotic drugs work ?
Vinca alkanoids and taxens both bind to beta tubulin disturbing the dynamics of microtubules. Vinca alkanoids prevent the polymerisation of microtubules whilst taxens stabilise pre-existing microtubules.
In ciliated cells where do microtubules grow out from ?
Basal bodies
How do microtubules act as tracks ?
The microtubules provide tracks whilst motor proteins (kinesins and dyneins) associate with the microtubule allowing cargo to be moved,
What is the structure of motor proteins and how do they work ?
They are diamers as they have a head and tail. The tail interacts with cargo whilst the head interacts with the microtubule. ATP dependent.
What is the role of actin ?
It is the thinnest and is needed for cell movement , through cell crawling. Involved in the support of microvilli and contractile bundles.
What is the structure of actin ?
Actin monomers pack tightly together to form 2 helices that are tightly wound,
What does actin associate with and why ?
different proteins which determines the function of the actin eg. a bundling protein.
What is the cell cortex ?
A specialised layer dense layer of actin that is cross linked, at the inner face of the membrane. It can associate with proteins that determine the shape of the cell , conferring shape.
What does spectrin do erythrocytes ?
Its in the cell cortex and cross links with actin providing the discoid shape of erythrocytes.
How do cells move using actin ?
Rearrangements of actin filaments within the cortex provide the basis for changes in cell shape and cell locomotion.
What is the extracellular matrix ?
A collection of extracellular molecules screted by cells to assist in the formation of tissue
In conenctice tissue which protein is preseent in the matrix ?
Collagen , interwoven with elastin
What is the structure of collagen ?
It is a rope like superhelix which consists of 3 lon polypeptide chains with glyceine at its core. There are cross linkages formed when bonds from between amino acids , making collageb fibrils. Also proline present.
What is the structure of elastin and how is it deposited ?
Loose unstructured polypeptides interowve with collagen. Cross linkls form between the elastin molecules allowing the formation of fibres. Fibrillin is secreted by the ECM and acts as a scaffold for the deposition of elastin. Elastin allows for arterial stretch as well as recoil.
What are glycosaminoglycans ?
Negatively charged polysaccharides , can be proteoglycans. Positively charged ions are attracted b, this lowers the water potential and draws water into tissue. This acts as a shock absorber by resisting compression. Present in dentine , stopping the enamel chipping. In the gingiva acts as a shock absorber
How is DNA found ?
DNA is highly condensed and packaged by proteins into chromatin. This is distributed among 24 diff chromosomes.
What are homologous chromosomes ?
Similar in length , gene position and centromere location. They contain different alleles
What are fundamental units ?
octamers- they are composed of 8 histone proteins which make up the nucleosome. 147 Base pairs stretcj around the nucleosome.
which histone proteins are present in the nuclesome ?
2 each of H2A H2B H3 and H4
What is a linker histone ?
A linker histone helps to pull nucleosomes together and pack them into a comapct chromatin fibre.
What is the structure of histone 1 ?
consists of a globular region and a pair of long tails at C and N terminal ends. The C terminal binds to chromatin allowing H1 to bind. This is because C end is larger.
What is heterochromatin ?
A region of the chromosome that is largely silent as the DNA is tightly wound.
What is euchromatin ?
It is more stretched and accessible DNA that is more likely to be expressed. (not all the time tho)
What are histone proteins ?
Proteins consisting of a high amount of positive amino acids ?
How do covalent modifications affect chromatin structure?
The amino acids in the histone have an N terminus amino acid tail that is positive and attracts modifications such as phosphate groups , acetyl groups and methyl groups.
How does acetyl and methyl modification work ?
Acetyl groups are negatively charged they repel negative DNA, hence the chromatin structure is unchanged. Methylation of a H3 protein is associated with gene silencing as heterochromatin forms.