BIOSCI MOD2 Flashcards
(187 cards)
1
Q
What is cell theory
A
- Alllivingorganismsarecomposedofoneormorecells
- Thecellisthebasicunitofstructureandorganisation
- Allcellsariseonlyfrompre‐existingcells
2
Q
what are 3 universal things about cells?
A
- DNAastheheritablematerial,RNAasanintermediaryor
messengerandproteinsastheworkers - Majorcellularorganelles‐ functionsandarrangements
withinthecell - ATPasanenergysource
3
Q
What do both prokaryotes and Eukaryotes have?
A
Bothhave:
Plasmamembrane,cytosol,
DNA,RNA,proteinand
ribosomes
4
Q
What is the main difference between Eukaryotes and Prokaryotes?
A
Eukaryoticcellshave membrane‐boundorganelles andaremuchlarger Prokaryotecellslacka membrane‐boundnucleus Eukaryoticcellshave membrane‐boundorganelles andaremuchlarger Prokaryotecellslacka membrane‐boundnucleus
5
Q
What is the definition of a cytoplasm?
A
Thecytoplasmiseverythinginsidetheplasmamembrane including
theorganelles,butnotincluding thenucleus
6
Q
What is the cytosol?
A
The fluid portion of the cytoplasm is the cytosol-water plus dissolved and suspended substances
7
Q
What is the plasma membrane
A
Theplasmamembraneisaselectivelypermeablebarrier
controllingthepassageofsubstancesinandoutofthecell
it is a physical barrier separating the inside and the outside of the cell
8
Q
What is a phospholipid
A
hydrophilicpolarheads(phosphate)
• hydrophobiclipidtails(fattyacids)
• arrangedasadoublelayeraroundcytoplasm,tailtotail
9
Q
What are plasma membrane proteins
A
they are the membrane proteins that mediate movement of hydrophilic substances
membrane proteins often have both hydrophobic and hydrophilic regions
10
Q
What are integral proteins?
A
plasma membrane proteins embedded (partiallyorfully)
intothemembrane
11
Q
what are transmembrane proteins
A
plasma membrane proteins integralmembraneproteinsthat fullyspantheentiremembrane, contactextracellularand cytoplasmicareas
12
Q
What are peripheral membrane proteins
A
associatedwiththemembrane,
butnotactuallyembeddedinit
13
Q
What is the point of plasma membrane proteins generally,(4)
A
allowcell‐cellidentificationandfacilitateintercellularcommunication
1) transport
2) enzymatic activity-carry out chemical reaction-may/may not be part of enzymes
3) signal transduction-external signalling molecule causing relay of infor to interior-usually a signal cascade
4) cell-cell recognition
5) intercellular joining
6) attachment to the cytoskeleton and the extracellular matrix
14
Q
fluid mosaic model
A
themembraneismosaicofproteinmolecules
bobbinginafluidbilayerofphospholipids
15
Q
Nucleus facts
A
Thelargestdistinctstructureinsidethecell Enclosedbydouble lipidbilayercalled nuclearenvelope, continuouswith roughER Entryandexitthroughnuclearpores
16
Q
what are the functions of a nucleus
A
- tohouse/protectDNAineukaryoticcells
- MakeRNAandassembleribosomes
- poresregulatemovementofsubstances(eg proteinandmRNA)inandout
- Moleculesegregationtoallowtemporal andspatial controlofcellfunction
17
Q
what is the function of a nucleolus
A
Nucleolus,rRNA production,assemblyofsmallandlargesubunitsofribosomes
18
Q
DNAstrandsneedstobepackedtofitintonucleus:
DNAwrapped2xaroundgroupof8histones,toform
nucleosomes collectivelyknownaschromatin
Ascellpreparesforcelldivision,condensesfurthertochromatin
fiberthencondensesfurtherinto loopsthenstacksas
chromosomes.Mostofthetime,ourDNAispresentas
chromatinandchromatinfibers
A
draaw
19
Q
what is a chromosome
A
comprises of many genes
20
Q
what is a gene
A
a dna segment that contributes to phenotype or function
21
Q
what are ribosomes
A
twosubunits,smallandlargemadeofribosomalRNA
(rRNA)incomplexwithmanyproteins
22
Q
what is the function of ribosomes
A
Function:proteinproduction(translation),foundintwoplaceswithinthecell:
freeinthecytoplasm‐ makingproteinstobeusedincytoplasm(non
endomembranedestinations)
OR attachedtotheRER ‐ makingnon‐cytoplasmicproteins/endomembrane
23
Q
What is the ER
A
TheERisanextensivenetworkof
tubesandtubules,stretchingout
fromthenuclearmembrane
24
Q
What are some of the features of rough ER
A
Continuouswithnuclearenvelope
Dottedwithattachedribosomes
proteinsenterlumenwithin theroughER forfolding RoughERmembrane surroundstheproteintoform transportvesiclesdestined for theGolgi
25
What are the major features of rough ER
Major function is production of:
• Secreted proteins
• Membrane proteins
• Organelle proteins
26
SER
Extends from the rough ER
Lacks ribosomes
doesn’t make proteins
27
What is the function of an ser
```
Major function is as a housing unit
for proteins and enzymes
Synthesizes lipids, including steroids
and phospholipids
Storage of cell‐specific proteins, not
all cells make all proteins
```
28
what are cisternae
membraneous sacs
29
What are functions of golgi apparatus
Functions:
modify, sort, package and transport
proteins received from the rough ER using
enzymes in each cisternae
Formation of:
• secretory vesicles (proteins for exocytosis)
• membrane vesicles (PM molecules)
• transport vesicles (molecules to lysosome)
30
how do proteins move in the golgi
from cis to trans, and they mature at the exit cisternae
31
what are lysosomes
and what are its main functions
vesicles formed from Golgi membrane that contain strong digestive enzymes
2)Membrane proteins pump H+ in
to maintain acidic pH within
```
Main function is digestion of:
• substances that enter a cell
• cell components e.g.
organelles ‐ autophagy
• entire cells ‐ autolysis
```
Once digested, all building blocks (amino acids, lipids, etc.) are recycled
32
What are our main categories of fuel
```
Our major categories of fuel:
• Proteins:
broken down to amino acids
• Fats:
broken down to simple fats
• Carbohydrates:
broken down to simple sugar
```
33
what are the net products of the citric acid cycle
```
Results in :
2 ATP
6 NADH
2 FADH
2
4 CO2
(per glucose molecule)
```
34
Where does the citric acid cycle occur?
in the mitochondrial matrix
35
what does the citric acid cycle require?
oxygen
36
what are FADH2 and NADH
FADH
| 2 and NADH are electron donors in the electron transport chain
37
Where does glycolysis occur
Occurs in the cytosol and oxygen is not required
38
what are some citric cycle intermediates used for
amino acid synthesis
neurotransmitter synthesis
fatty acid synthesis
gluconeogenesis
39
What does it mean for a series of reactions
product of the first reaction is a substrate for the next
40
what is substrate level phosphorylation
ATP is generated by the direct transfer of a
| phosphate group to ADP
41
what processes in the mitochondria undergo substrate level phosphorylation
Glycolysis and Citric acid cycle make ATP via
| substrate phosphorylation
42
how many atp does chemiosmosis produce
This results in the production of 26 or 28 ATP
43
how many atp does oxidative phosphorylation produce
0
44
cellular respiration is versatile
it can derive energy from more than just carbohydrates
45
how is cellular respiration controlled?
Phosphofructokinase can be rate
limiting for glycolysis
it is inhibited by citrate and ATP
(though can be stimulated by AMP)
negative feedback control-integral to the production of atp
46
what is the role of insulin
Produced by beta cells of Islets of Langerhans in pancreas
• Function: promote glucose uptake into cells (for ATP
production or storage in liver
47
what is the role of glucagon
• Produced by alpha cells of Islets of Langerhans in pancreas
• Function: Stimulates the breakdown of glycogen to increase
blood sugar levels
48
what happens if you lose function of insulin
No glucose in cells
• No ATP from glucose
• No glycogen “for a rainy day
49
type 1 diabetes
Body does not produce insulin, as beta cells of pancreas are destroyed,
often this is autoimmune, or genetic or through environmental factors
• Affects 5 – 10 % of diabetics, and onset usually occurs in children or
adolescents.
• Requires insulin replacement
50
type 2 diabetes
* Body produces insulin, but receptors are non functional (insulin resistance)
* Most (>90%) diabetics are Type II, usually adults over the age of 40
* Can be linked to other pathogies and obesity, but not sure how or why
* A very active area of research
51
is the mitochondria part of the endomembrane system?
nope
52
anatomy of mitochondria
```
Mitochondria are made up of:
• Outer mitochondrial membrane
• Inner mitochondrial membrane, with
folds called cristae
• Fluid filled interior cavity, called the
mitochondrial matrix
```
53
other stuff about mitochondria
The more energy a cell requires, the more
ATP it must make, the greater the number
of mitochondria present in that cell.
Mitochondria carry a separate small (37 genes) genome encoding mitochondrial specific products2
54
what is the point of the cytoskeleton
```
Fibres or filaments that help to
maintain the size, shape and
integrity of the cell:
•Act as scaffolding across the cell
•Involved in intracellular
transportation and cell movement
```
55
microfilaments
Comprised of actin molecules assembled in two long
chains, twisted around each other
30
Assembled and disassembled as required ‐ dynamic
Function:
Bear tension and weight by anchoring cytoskeleton to plasma membrane
proteins, and promote amoeboid motility if required (eg. macrophage)
Found around the periphery and lining the interior of cell
56
intermediate filaments
Diameter: 8‐12 nm.
Comprised of diverse range of different materials; one example: keratin
Found in the cytoplasm of the cell.
Diameter: 8‐12 nm.
Comprised of diverse range of different materials; one example: keratin
Found in the cytoplasm of the cell.
Usually the most permanent of cytoskeleton
bear tension and weight throughout cell, e.g., during cell anchoring,
• act as scaffold for cellular organelles, e.g., the nucleus.
57
microtubules
gella
Functions:
• Support cell shape and size
• Guide for movement of organelles,
• e.g., vesicles from Golgi to membrane
• Chromosome organization – cell division
• Support and movement of cilia /flagella
32
Diameter:
: tubular structure, 25 nm with central lumen of 15 nm diameter
Comprised of tubulin dimers (alpha and beta), coiled, to form a tube
Extends from centriole into cytoplasm/nucleus
Assembled and disassembled as required ‐dynamic
58
What is an organism's genotype
an organisms hereditary information
59
What is an organism's phenotype
actual observable or physiological traits
60
what is meant by gene expression
the process of going from DNA to a functional product
61
definition of DNA
is the heritable material that is used
to store and transmit information from
generation to generation
62
what is RNA
acts as a messenger to allow the
information stored in the DNA to be used to
make proteins
63
What are the 3 main steps of creating a protein
Transcription of RNA from DNA
Processing of the pre‐mRNA transcript
Translation of the mRNA transcript to a protein
64
How is gene expression tightly regulated
```
1)Transcription factors need to
correctly assemble and DNA needs to
be accessible.
2)Most control is at this point.
Capping, extent of polyadenylation,
alternate splicing, producing a stable
3)mRNA able to be translated
specific proteins assist
in the export of mRNA
4)Regulatory proteins can block
translation, variable mRNA life‐spans
```
65
What types of proteins are transcribed
Housekeeping proteins are actively transcribed from DNA continuously
• Protein and mRNA are present in large quantities (e.g. Tubulin)
• Typically have long half life in cells
Housekeeping proteins are actively transcribed from DNA continuously
• Protein and mRNA are present in large quantities (e.g. Tubulin)
• Typically have long half life in cells
Other proteins are produced in response to stimuli as required
• Cell signaling (e.g. ligand binding a cell surface receptor, or activating an
intracellular receptor)
• Signal transduced and may enter nucleus to activate transcription
• results in the production of a short‐lived protein to carry out the required
function
66
Define anabolism
| Define catabolism
Anabolism means building up
| Catabolism means building down
67
What is the function of catabolic reactions
They help transfer energy from complex molecules to ATP. Complex molecules being things such as glycogen, proteins and triglycerides
68
What is the function of anabolic reactions
transfer energy from ATP to complex molecules
69
What is the definition of the ATP cycle
the transfer of energy between complex and simple molecules in the body, with ATP as the mediator
70
What are our 3 major sources of fuel and what are they broken down to
Proteins
Fats
Carbohydrates
Proteins are broken down to amino acids
Fats are broken down to simple fats
Carbohydrates are broken down to simple sugars
71
How is energy lost in the fuel is needed to generate atp
heat, energy lost in nitrogenous waste
72
Where does glycolysis occur
cytosol
73
What is pyruvate oxidation and where does this happen
pyruvate oxidation is causing the formation of Acetyl Coenzyme A
and it happens in the mitochondrial matrix
74
Where does the citric acid cycle occur
citric acid cycle happens in the matrix of the mitochondria
75
Where does oxidative phosphorylation occur
across the inner membrane
76
Is oxygen required for glycolysis
nope
77
what happens in glycolysis
2 ATP are invested
4 atp PRODUCED
2 nadh are produced
78
Is oxygen required for pyruvate oxidation
yes
79
What is the role of pyruvate oxidation
it links glycolysis to the citric acid cycle by forming acetyl CoA
80
What are the products of the pyruvate oxidation
no ATP
1NADH per pyruvate
CO2(per pyruvate I'm assuming)
Acetyl group
81
What are the products of the complete citric acid cycle
2ATP
6NADH
2FADH2
4CO2
(per glucose molecule)
82
What happens to citric cycle intermediates
The intermediates are used to synthesise lots of other stuff
```
LIKE fatty acids
amino acids
neurotransmitter
amino acids
glucose
```
83
What is meant by a series of reactions and is the citric acid cycle considerred to be one
Yes, the citric acid cycle is considerred to be a series of reaction
This is when a product of the first reaction is the substrate for the next
84
Define substrate level phosphorylation
| and which two parts of the process
glycolysis and citric acid cycle; use substrate phosphorylation
it is defined as the direct transfer of a phosphate group to ADP
85
what is the definition of oxidative phosphorylation
ATP is generated from the oxidation of NADH and FADH2 and the subsequnt transfer of electrons and pumping of protons
86
how many ATP is produced in the ETC
26 to 28
87
WHy is 26-28 ATP produced in electron transport chain and chemiosmosis, why not just 26 and why not just 28
Phosphorylation and redox reactions are not directly coupled, so have a ratio rather than a straight number
Energy stored in the H+ gradient may be used solely to produce ATP or may be split between making ATP and powering other mitochondrial processes
Glycolytic NADH electrons must be shuttled into the mitochondria, and transferred to either NAD+ or FAD, The latter of which promotes production less ATP
88
Give the steps of the electron transport chain
NADH and FADH2 are oxidised to donate 1 or 2 electrons
electrons transfer from protein to protein along the chain in a series of redox reactions
At each transfer, each electron gives up a small amount of energy which enables H+ ions to be pumped into the intermembrane space.
OXYGEN PULLS THE ELECTRONS DOWN THE CHAIN AND IS THEN THE FINAL ELECTRON ACCEPTOR WHERE IT IS REDUCED TO WATER
89
What is chemiosmosis and what is the process
The hydrogen ions in the intermembrane space rush down their concentration gradient through ATP synthase.
This causes the turbine within ATP synthase to turn
90
what does it mean that cellular respiration is versatile
We can derive energy from more than just glucose,
fats, proteins and more complex carbohydrates generate ATP also
monomers enter glycolysis and the citric acid cycle at different points
91
How is cellular respiration controlled
Phosphofructokinase limits rate for glycolysis
Negative feedback control is integral to the production of ATP
92
Definition of homeostasis
the maintenance of relatively constant conditions within physiologically tolerable limits
93
What are the functions of insulin
| and where is it produced
produced by beta cells of islets of langerhans in the pancrease
Function: promote glucose uptake into cells (for ATP production or storage in liver)
94
What are the functions of glucagon
| and where is it produced
produced in the alpha cells of islets of langerhans in pancrease
it stimulates the breakdown of glycogen to increase blood sugar levels
95
What is diabetes mellitus
| what are some of its side effects
the ability to produce or respond to insulin hormone impaired
results in abnormal metabolism of carbohydrates and elevated levels of glucose in blood
96
What generally happens when you lose the function of insulin
no glucose in cells
no ATP from glucose
no glycogen "for a rainy day"
97
What is type 1 diabetes
who does it usually affect
how is it often treated
Body does not produce insulin, as beta cells of pancreas are destroyed, this is usually genetic, or autoimmune
Since it is a genetic disease, it often happens in children and adolescents
The treatment requires insulin replacement
98
What is type 2 diabetes
body produces insulin, but receptors are non functional
happens mostly to adults over age of 40 (queen the plague)
It is often linked to other pathogies and obesity, but it is unclear why
Treatment options include careful energy intake management
some drugs
99
Why is extreme hunger and constant eating and unexplained weight loss symptoms of diabetes
The lack of functional insulin means that glucose is not able to get inside the cells to make ATP so the body asks for more glucose from both food and body stores
100
List 10 different side effects of diabetes
```
excessive thirst
frequent urination
extreme hunger or constant eating
unexplained weight loss
presence of glucose in urine
tiredness or fatigue
changes in vision
numbness or tingling in extremeties
slow healing wound or sores
```
abnormally high frequency of infection
101
What is initiation of transcription
Assembly of multiple proteins required before transcription can commence
102
What are the 3 main steps of initiation
Transcription factors are made, and several transcription factors bind to DNA( i assume near the promoter region)
After TFs bind, RNA POLYMERASE ii can now bind along more TFs to form the transcription initiation complex
transcription begins
103
What happens during elongation
10-20 nucleotides exposed at a time when unwound
Complementary RNA nucleotides added to 3' end of growing transcript
double helix reforms as transcript leaves the template strand
104
what happens at t Termination
after transcription of the polyadenylation signal, nuclear enzymes release the pre-mRNA and RNA polymerase then dissociates from the DNA
N.B, proofreading less than for DNA replication
105
what are some steps for mRNA processing
capping: a modified guanine nucleotide is added to the 5' end
Tailing:50-250 adenine nucleotides are added to the 3' end
106
What is the point of mRNA processing
facilitate export, confer stability, facilitake ribosome binding once in cytoplasm
107
splicing
introns are removed from the transcript
108
What are exons
coding regions including things called UTRs-untranslated regions at 5' and 3' ends
109
what are introns
non-coding regions intervening exons
110
Where does splicing occur
at the SPLICEOSOME. the SPLICEOSOME is within the NUCLEUS
111
What is a spliceosome
a large complex of proteins and small RNAs
112
How does splicing occur
What determine splcing
introns are removed from the transcript and rejoined to form mature mRNA
short donor and acceptor sequences near the ends of the introns determine splicing.
mutations in these splice sites can affect generation of gene produc
113
What is alternative splcing
splicing of DNA at different sites
it allows for multiple gene products from the same gene
114
What is the wobble hypothesis
How is it derived
that tRNAs can base pair to more than one codon.
there are 64 possible codons, 61 of which code for amino acids, but there are only around 40 tRNAs as tRNAs can base pair to presumably to more than one codon
115
what is translation-
when mature mRNA transcript exits nucleus and is bound by the ribosome
116
What is the overview of translation
codons are translated into amino acids
tRNA molecules within the ccytosol with specific anticodons carry corresponding amino acids
Hydrogen bonds form between mRNA and anticodon of appropriate tRNA
The amino acid is added via peptide bonds to the growing polypeptide chain
117
What are the functions of a ribosome
ribosome has binding sites for mRNA and tRNA
tRNA and mRNA held within ribosome to enable to formation of the polypeptide
118
what does the A site do
holds next in line tRNA
119
what does the P site do
holds tRNA carrying the growing polypeptide
120
what does the e site do
tRNAs exit from here
121
what is a tRNA
it is a physical link between the mRNA and the amino acid sequence of proteins
122
what happens during translation initiation
an initiator tRNA=a tRNA carrying methionine is needed
the small ribosomal subunit with initiator tRNA already bound binds to the 5' cap of mRNA
the small ribosomal subunit scans downstream to find the translation start site
Hydrogen bonds form between initiator anticodon and mRNA
Large ribosomal subunit then binds- completing initiation complex
GTP needed for the assembly of the translation initiation complex
123
What happens in the elongation phase of translation
1) codon recognition
2) peptide bond formation
3) Translocation
124
What is the codon recognition phase of translation
happens in elongation
it is when base pairs with complementary anticodon.
here GTP is invested to increase accuracy and efficiency
125
What happens during the peptide bond formation phase of translation
happens during elongation
A large subunit rRNA catalyses peptide bond formation
and removes it from tRNA in P site
126
what happens during translocation
moves tRNA from A to P site
tRNA in P site moves to E and is released.
Energy is required
127
what happens to the empty tRNAs after elongation
empty tRNAs are reloaded in the cytoplasm using aminoacyl tRNA synthetases
128
What happens at the termination step of translation
Ribosomes reaches a stop codon on mRNA
this causes release factor that promotes hydrolysis
the ribosomal subunits and other components dissociates
129
Explain what happens when a ribosome reaches a stop codon on mRNA
Mrna STOP CODON IN THE a SITE IS BOUND BY A RELEASE FACTOR
130
What happens to the bond between the p site tRNA and last amino acid when it is hydrolysed
polypeptide made is released
131
What is needed for the ribosomal subunits and other components to dissociate in the translation termination step
hydrolysis of 2 GTP molecules
132
what determines the properties of each amino acid
The side chains
133
What is a primary structure
it is a structure determined by DNA sequence and it is held by covalent bonds between amino acids
it starts to form secondary structures as soon as it leaves the ribosome
134
What is the N terminus and C terminus
N terminus is the amino end of the amino acid, and the C terminus is the carboxyl end of the acid. It should be noted that protein is coded from N to C i THINK
135
What is a key component of secondary structures
secondary structures include alpha helices and beta pleated sheets that are held together by hydrogen bonds
136
What is a tertiary structure
a tertiary structure is a 3D shape stabilized by side chain interactions.
The bonds often includes hydrgophobic interactions, hydrogen bonds
and sometimes disulphide bonds
137
What is the definition of quaternary structure
multiple proteins associate to form a functional protein. May be homo or hetero
138
what are the chaperone proteins
proteins that help with folding of polypeptide chains into tertiary structure
139
what is a signal peptide
at the N terminus of the protein, the small strip is known as a signal peptide
it directs ribosomes to the RER methinks(thats what chen says_
wikipedia says: Signal peptides function to prompt a cell to translocate the protein, usually to the cellular membrane. In prokaryotes, signal peptides direct the newly synthesized protein to the SecYEG protein-conducting channel, which is present in the plasma membrane. A homologous system exists in eukaryotes, where the signal peptide directs the newly synthesized protein to the Sec61 channel, which shares structural and sequence homology with SecYEG, but is present in the endoplasmic reticulum.[3] Both the SecYEG and Sec61 channels are commonly referred to as the translocon, and transit through this channel is known as translocation. While secreted proteins are threaded through the channel, transmembrane domains may diffuse across a lateral gate in the translocon to partition into the surrounding membrane.
140
what does the signal recognition particle do
the signal recognition particle recognises the signal peptide, and then it retards elongation and docks to the receptor
141
what is the overview of the fate of protein (6 steps)
1)Polypeptide synthesis begins
2)SRP binds to signal peptide
3) SRP binds to receptor protein
4) SRP detaches and polypeptide synthesis resumes
5) signal cleaving enzymes cuts off signal peptide
the completed polypeptide folds into final conformation
142
in the ER lumen, what happens to a secretory protein and what happens to a membrane protein when the completed polypeptide folds into final conformation
A secretory protein is solubilized in lumen, while a membrane protein remains anchored to the membrane
Both then go to the golgi via vesicles for further maturation
143
Why do we need post-translational modifications
translation is now complete but the protein may not yet be functional
144
What do some post-translational modifications do to a protein
it can confer activity-via phosphorylation or enzyme cleavage
it can confer an ability to interact with other molecules- this includes biotinylation, methylation of histones
or this can direct proteins towards particular locations- e.g ubiquitination for proteasome degradation
ULTIMATELY ALL OF THIS PROVIDES ANOTHER LEVEL of REGULATION
145
What are the three main steps of a transduction method of cell signalling
reception
transduction
respons
146
What happens at reception
signalling protein binds to a receptor protein and allows or causes the activation of a protein
147
What happens during transduction
the activated protein may cause a relay of changes, this when relay molecules known as second messengers and other proteins may be activated
a common example includes the phosphorylation cascade
148
Why are receptors specific
human body sends many chemicals- gotta be specific if we want to activate a target receptor
only certain cells at certain times will have particular receptors meaning that while the signal might be widespread the transmission of the signal occurs only where it is needed
149
What are the 2 kinds of receptors
intracellular receptors
| membrane bound-cell surface receptors
150
Describe intracellular receptors
primary messenger is generally hydrophobic and/or small-lipid soluble, it can cross PM.
this typically includes sex hormones and thyroid hormones
after it crosses, it causes a significant change
151
Describe membrane bound cell surfce receptors
primary messenger is generally hydrophilic and need help to cross PM
152
what are GPCRs
G protein coupled receptors
these are typically transmembrane proteins and have the weird feature of passing the PM 7 times. there are many different ligands and have diverse functions
153
what are G proteins
G proteins are molecular switches which either are on or off depending on whether GDP or GTP is bound
154
generally how does a GPCR work
at rest, the receptor is unbound and G protein is bound to GDP, the enzyme is in an inactive state
the ligand then binds to receptor and binds the G protein. GTP displaces GDP. the enzyme is still inactive
the activated G protein dissociates from recptor. Enzyme is activated to elicit a cellular response
G Protein has GTPase activity promoting its release from enzyme and reverting it back to resting state
155
explain the basic mechanism of a ligand gated ion channel
binding of ligad at specific site on receptor elicits change in shape
the channel opens or closes as the receptor changes shape
ions can then pass through channel
156
what do protein kinases do
protein kinases are enzymes that transfer a phosphate group from ATP to another protein
series of protein kinases each add a phosphate to the next kinase
157
what do phosphatases do
they are enzymes that dephosphorylate, rendering the protein inactive-but recyclable
158
how is calcium often used as a common second messenger
conc grad- usually theres a low calcium concentration inside the cell and very high calcium concentration outside the cell.
The maintenance of concentration via calcium pumps important
159
Why are there so many steps in cell signalling
it amplifies the response
provides multiple control points
allows for specificty of response
allows for coordination with other signaling pathways
160
Why do somatic cells divide?
growth and development, tissue renewal
results in 2 daughter cells that are genetically and functionally identical to the parent cell
161
Do all somatic cells divide?
many, but not all.
Some like muscle cells don't divide at all
162
What stages are found in the interphase
growth-aka gap phase 1
Synthesis of DNA-aka S phase
growth phase 2, G2
163
What happens in G1
most cellular activities occur here;
cells here are metabolically active, the duplication of organelles and cytosolic components happen
Centrosome replication begins
164
What happens in G0
known as the resting phase, it is a cellular state outside of the replicative cell cycle
165
what is the cell cycle
it is the series of events that take place in a cell leading to duplication of its DNA
166
What happens in the S phase
DNA replication occurs
strands are separated at the hydrogen bonds holding the nucelotides together
new strand of DNA is synthesized opposite each of the old strands
167
What happens in the G2 phase
checks for correct DNA synthesis-it prepares for the mitotic phase
Cell growth continues
enzymes and other proteins are synthesized
Centrosome replication repeated
168
How long does the following take;
G1 phase
S phase
G2 phase
g1= 8-10 hrs
S=8 hrs
G2=4 to 6 hours
169
what does the mitotic phase include
mitosis plus cytokinesis
170
What are sister chromatids
sister chromatids are the two identical chromatids per chromosome
sister chromatids are 2 identical copies of the same chromosome formed by DNA replication attached to each other by a structure called a centromere
171
what are the 3 checkpoints called
M checkpoint, G2 check point and G1 checkpoint
172
what are the 3 key regulatory molecules for G2 and what are their functions
Cyclin: a protein that fluctuates throughout the cell cycle. It pretty much attaches to target kinases and direct the Cdk to a specific set of target proteins
Cyclin dependant kinase (Cdk): a kinasethat is activated when attached to a cyclin: kinases phosphorylate protein making it more active
M phase promoting factor: an cyclin and a Cdk bound to its M cyclin partner
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what are the G1 "checkpoints" for cell division
1) undamaged DNA
2) Cell size
nutrition
3) appropriate signals
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what are the M checkpoints
All chromosomes are attched to spindles
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What happens when a cell does not pass the G1 checkpoint
cell enters G-0, EXITS CELL DIVISION
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what happens when the cell does not pass the M checkpoints
stop signal received, and cell division goes towards a halt
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How does DNA become changed
could be the result of an acquired change
or inherited change
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what are the 2 commonly affected genes
proto-oncogenes- genes that stimulate cell proliferatio
or
Tumor suppressor genes-genes that keep proliferation in check
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What happens when tumour suppressor genes lose function
it causes a loss of brakes
it means that cell division not under control
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what are 3 examples of tumor suppressor gene
TP53, brca1, brca2
| APC, SMAD4
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what are 2 examples of oncogene
Ras- a GTPase
| and Myc- a transcription factor
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what is a proto oncogene
A normal cellular gene that encodes a protein usually involved in regulation of cell growth or proliferation and that can be mutated into a cancer-promoting oncogene, either by changing the protein-coding segment or by altering its expression
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what is an oncogene
A gene whose product is involved either in transforming cells in culture or in inducing cancer in animals. Most oncogenes are mutant forms of normal genes (proto-oncogenes) involved in the control of cell growth or division
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why does an oncogene cause cancer
oncogene provides an excessive or uncontrolled growth promoting signal
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how does a carcinoma form
Loss of tumor suppressor gene such as APC
causes a small polyp to form
2) activation of ras oncogene
3) loss of tumor suppressor gene SMAD4
this may cause the growth of a larger benign growth - an adenoma
4) loss of tumor suppressor gene -53 and additional mutations causes carcinoma.
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What are primary human cells
cells that are directly cultured from their source organ tissue
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what are immortalised human cell lines
cell which would normally not proliferate indefinitely but have evaded normal cellular senescence
