Self study Flashcards
What can you said about the DNA?
-DNA is a helix with 10 bases per turn.
-The sugar-phosphate backbone of the DNA is composed of deoxyribose molecules.
- The two DNA strands are complementary
- DNA has a chemical polarity (5 to 3)
What is the difference between interphase chromosomes and mitotic chromosomes?
Interphase: extended shape, replication and expression of the genes
Mitotic: condensed to enable their segregation during cell division
What can you said about DNA replication
-DNA replication can only work in the 5’- 3’ direction of a DNA strand.
-DNA replication is semi-conservative.
-DNA replication is mediated by polymerase
What can you say about regulation of chromosome structure?
-Decondensation of chromatin via the remodeling complex requires ATP.
- Histone modifications can alter the stability of the chromatin fiber.
- Chemical modifications of histones serve as docking sites for regulatory proteins.
- The accessibility of DNA can be modified by the chromatin-remodeling complex.
Mention some essential structures for chromosome segregation?
-Chromatid
- Kinetochore
- Centromere
Mention some elements of the chromosomes
-Retrotransposons
- exons
- short and long interspersed nuclear elements
- mobile genetic elements
Of what is composed a nucleoside?
A base and a sugar
What are the number of hydrogen bonds between G-C and A-T?
G-C : 3 hydrogen bonds
A-T : 2 hydrogen bonds
What does/is a karyotype?
- Compares one set of chromosomes to another.
- Identifies abnormalities in the number of chromosomes.
- Is a photograph of cells undergoing mitosis during anaphase.
- Cannot be used to identify individual chromosomes beyond the fact that two
chromosomes are homologues. - Is a visual display of chromosomes arranged according to size.
Of what is composed a nucleotide?
Of a base, phosphate and a sugar
How is composed a gene and what produces?
Of a coding strand and a complementary strand and its products are
RNA and protein.
What type of chromatin contain interphase chromosomes?
Euchromatin
Heterochromatin
What can you say about hetero- and euchromatin?
- Heterochromatin contains few genes and is densely packed.
- The formation of heterochromatin is required for silencing of one X-chromosome in female mammals.
- Euchromatin is rich in genes and less compact than heterochromatin.
Mention some structural characteristics that can be found in a DNA double helix?
- 2 parallel DNA strands (but antiparallel)
- hydrogen bonds
- desoxyribose
- major groove
Mention the pyrimidines and the purines
- Thymine and cytosine are pyrimidines.
- Adenine and guanine are purines.
Only 1,5% of the human genome code for proteins?
True
Genes contain a coding strand and a complementary strand?
True
The chromosomal DNA forms complexes with…
histone H2A and H2B
histone H3 and H4
Histones contain a high proportion of + or - charged amino acids?
positively, This enables the
electrostatic interaction with the negatively charged sugar-phosphate backbone of the DNA
The replication of DNA is?
Semiconservative, proven by the Meeselson-Stahl experiment which showed that each daughter DNA double helix is composed of 1 conserved
strand and 1 newly synthesized strand.
What can you say about DNA replication?
- The parent DNA double helix is composed of an S strand and an S’strand.
- Initiator proteins recognize replication
- Replication origins are rich in A and T.
What is the function of DNA Polymerse?
Adds new nucleotides to the 3’ end of the growing DNA strand.
What is the function of primase?
Makes a short RNA primer and is able to begin new strand without need for basepaired
end.
What is the function of Nuclease?
Degrades the RNA primer.
What is the function of the repair Polymerase?
Replaces the RNA primer with DNA and is required for proofreading.
What is the function of DNA ligase?
Joins the 5’ end of one fragment to the 3 end of the next which requires ATP.
What is the function of DNA helicase?
Unwind(s) the DNA strands and breaks the hydrogen bonds between the two strands.
What is the function of Single strand binding protein?
Bind(s) to DNA to keep the strand in its elongated form.
What is the function of DNA topoisomerase?
Produce(s) transient nicks to release tensions and seals the nicks
What is the function of Sliding Clamp?
keep(s) DNA polymerase firmly attached to the DNA.
What is Clamp holder?
lock(s) sliding clamp around a newly formed double helix thereby hydrolyzing ATP.
Which strategies can be used by a cell to repair the damage of both strands during DNA replication?
- non-homologous end joining
- homologous recombination
Which of the following proteins are required for DNA replication?
- single-strand DNA binding proteins
- DNA helicase
What can be said of DNA replication?
- The direction of chain growth during DNA replication is 5’ -3 .
- During DNA replication, 2 replication forks move away from the replication origin in
opposite directions.
Homologous recombination…
- is technologically applied for gene targeting and protein engineering.
- … takes place during DNA double-strand break repair.
- … requires a repair polymerase.
- … takes place during meiosis and results in new combinations of DNA sequences.
What can you said about telomers and telomerase?
- Telomers are long, repetitive sequences capping the ends of chromosomes.
- The telomerase prevents the loss of DNA during cell division.
- The DNA polymerase completes the lagging strand after telomer extension.
- The telomerase carries a short piece of RNA which serves as a template for the
telomers.
Which types of DNA damage continually occur in our cells?
- Depurination
- deamination
- formation of thymine dimers
RNA contains ribose. Whereas DNA …
- Whereas DNA contains desoxyribose.
RNA is usually…
- Single stranded
Uracil can be found in—
- RNA instead of Thymine
RNA folds into three-dimensional structures via …
- short stretches of non conventional basepair interactions within the molecule
mRNAs…
code for proteins.
rRNAs…
form the basic structure of the ribosome and catalyze protein synt
tRNAs…
central to protein synthesis as adaptors between mRNA and amino
snRNAs…
funchon in a variety of nuclear processes, including the splicing of pre
Transcription of a gene produces an RNA complementary to…
- the template strand of the DNA
What need DNA transcribed by RNA polymerase
needs NO primer and NO proofreading
Due to the almost immediate release of RNA from DNA
it is possible to make many RNA copies from the same gene in a short time
What are the functions of the transcription factors: TFIIF, TFIIE, TFIIH? (of transcriphon by the eukaryohc RNA polymerase I)
TFIIFstabilize(s) RNA polymerase interachon with TBP and TFIIB; helps ajract TFIIE and TFIIH.
TFIIE ajracts and regulates TFIIH.
TFIIH unwinds DNA at the transcriphon start point, phosphorylates Ser5 of the RNA
polymerase CTD (C-terminal domain): releases RNA polymerase from the promoter.
What are the functions of the transcription factors: TFIIB, TFIID TBP, TEIID TAF? (of transcriphon by the eukaryohc RNA polymerase II)
TFIID TBP subunit recognize(s) TATA box.
TFIIB recognize (s) BRE element in promoters; accurately posihons RNA polymerase at the
start site of transcriphon.
TEIID TAF subunits recognize (s) other DNA sequences near the transcriphon start point;
regulate(s) DNA-binding by TBP.
Consensus sequences serve as binding sites for transcriphon factor to the DNA…
TFIlB binds to the BRE element.
TFIID binds directly to the INR element which contains the transcriphon start point and to
the DPE element.
TBP binds to the TATA box.
What proteins are part of the transcriphon inihahon complex?
- RNA pol II
- TFIIH
- TFIIF
- TFIIB
- TFIIE
What are the differences and commonalihes between eukaryotic and prokaryotic
transcription?
- Eukaryotic cells have three RNA polymerases compared to only one RNA
polymerase in prokaryotic cells. - Eukaryotic DNA is packed into nucleosomes while prokaryotic DNA is easily
accessible. - Eukaryotic polymerases require the assistance of numerous proteins.
- Eukaryotic transcription is under the control of a large variety of regulatory sequences.
Mention steps on the way from the gene to protein.
- transcription
- processing
- export to the cytoplasm
- translation
Eukaryohc RNA is processed in the nucleus amer transcription. List the three processing steps
- capping
- splicing
- tailing
The process of splicing removes noncoding regions, termed ___________ from the mRNA.
introns
Splicing is carried out by …
snRNPs (small nuclear ribonucleoproteins)
During splicing, ribonucleoproteins….
catalyze the covalent linkage of exon sequences
Describe capping
- the 2’ OH of the second ribose is often addi]onally methylated
- a guanosine bearing a methyl group is attached to the 5’ end in an unusual way
- the process starts already afterer the produc]on of about 25nt RNA
Describe tailing
- an enzyme cuts the RNA at a particular sequence
- the 3’ end is trimmed - a series of repeated adenine nucleotides are added
A specialized set of RNA-binding molecules signals that a mature mRNA is ready for export to
the cytosol. Which proteins are included in this set?
- exon junc]on complex
- polyA binding protein
- cap binding protein
What are the functions and effects of RNA processing?
- facilitates the export of the mRNA to the cytoplasm
- marks the RNA molecule as mRNA
- enables the protein-synthesis machinery to make sure that both ends of the mRNA
are present indicating that the mRNA is complete - increase of stability of mRNA
During translahon, the mRNA us read from…
5’ to 3’ end
During translation, the peptide is synthesized from …
from the N to the C terminus
An mRNA can be translated in how many possible reading frames?
3
Ribozymes are RNA molecules that possess …
- catalytic activity
How describe ribosomes?
- they capture complementary tRNA molecules and hold them in position
- they contain 3 binding sites for tRNA
- they are composed of 2 subunits
- they covalently link the amino acid of the tRNA to the growing polypeptide chain
Mention features of tRNAs
- It contains unusual bases which are derived from uracil.
- It contains 4 double helical regions.
- It is an adaptor between codon an amino acid.
- It harbors the anticodon on one side and the attached amino acid on the opposite side.
Mention the function of Chloramphenicol, Rifamycin and Cycloheximide
Chloramphenicol: blocks the peptidyl transferase reaction on ribosomes.
Rifamycin: blocks initiation of transcription by binding to RNA polymerase.
Cycloheximide: blocks translocation reaction on ribosomes.
Mention the ribosome subunits and its functions
Large subunit catalysis of the formation of peptide bonds.
Small subunit matching tRNA to codons of mRNA.
The final concentrahon of proteins depends on …
- the rate of each step combined (transcription, processing, export, transla]on, folding, degradation)
The final activity of a protein depends on …
- correct folding, modifications and binding to cofactors
Proteasomal degradation of proteins depends on ..
- the addition of a polyubiquitin chain
The initiator tRNA…
- carries methionine
- is loaded into the P-site with translation initiation factors
- is capable of binding tightly to the mRNA in the absence of the large ribosomal subunit
Mulhple ribosomes usually bind to each mRNA being translated?
TRUE
Whta is the name of the polymerase subunit that recognize the promoter in bacterial RNA polymerase?
Sigma
What is the function of the sequence of the promoter?
Orient the RNA polymerase and determines which DNA strand is transcribed
Which DNA damage repair mechanisms exist for which scenario?
1 strand damaged: Base excision and nucleotide excision (second strand can be used as a template).
both strands damaged: homologous repair and non-homologous repair (second
chromosome is used as a template).
The consequences of errors during DNA replication?
deletions , mismatches and
point mutations. Errors made during DNA replication must be corrected to avoid permanent
mutations in one of the two DNA molecules
A cluster of bacterial genes transcribed as one mRNA from one promoter is called?
Operon
mRNA is stable for up to 30 minutes and in some cases even for more than 10 hours in?
Eukaryotes
Cell differentiation arises because cells make and accumulate different sets of RNA and proteins?
True
The total protein content of a cell can be analyzed by 2-dimentional gel electrophoresis and mass spectrometry.?
True
Cells express house warming genes and regulated genes?
False
Differentiated cells contain only the genetic instructions necessary for one cell type?
False
Various cell types of an organism differ because they differentially express genes.
True
Transcription regulators bind to specific sequences which are necessary for the initiation of transcription, namely the ?
Promoter
Transcription factors interact with the ….. groove of the double helix
major
Transcriptional regulators often bind as dimers, thereby doubling the area of contact and generating many possible combinations. Their interaction with DNA is…
Highly specific
Prokaryotic transcription can be regulated by …… binding to the operator and preventing the recruitment of the RNA polymerase.
represors
Prokaryotic transcription can be regulated by …. binding next to the promoter to help position the RNA polymerase.
Activators
In eukaryotes, gene activators can only bind to the DNA 50 bp upstream of the TATA box?
False
First, general transcription factors and the RNA polymerase bind to the DNA.
TRUE
Activators and repressors influence the assembly of the transcription initiation complex?
TRUE
Proteins modifying the chromatin structure do not affect the accessibility of the promoter.
False
The effects of multiple transcription regulators combine the determine the final rate of transcription initiation.
True
One single protein can only control the expression of one single gene.
False
Which mechanisms contribute to the maintenance of the identity of differentiated cells?
- Positive feedback loops
- DNA methylation
- Modification of histones
“Cell memory” means that the patterns of gene expression in each cell can not be passed on to daughter cells.?
False
A riboswitch can be best described as …
- a short sequences of RNA that changes its conformation when bound to other small molecules
Alternative splicing allows …
- switching from membrane-bound to secreted proteins
- transcription of cell type specific forms of proteins
RNA editing can lead to
- altered mRNA binding properties
- a premature stop codon
- altered mRNA transport
- different splicing pattern
- amino acid change
mRNA transport is determined by…
3’UTR
5’ cap and 3’ poly-A-tail are known to influence
- translation initiation
- deadenylation-dependent mRNA decay
In eukaryotes, mRNA can be stable to up to
10 hours
RNA interference CANNOT lead to..
- active degradation of RNA polymerase
Which of these small non-coding RNAs influence gene expression?
- piRNA
- miRNA
- siRNA
One single miRNA can control
- a set of mRNAs
Which proteins are involved in the generation and action of siRNAs?
- Argonaute
- RNA polymerase
- RISC complex
The CRISPR system original biological function is..
- a defence mechanism against viral infection
Humans express more than … long non coding RNAs.
30000
What are the functions of intermediate filaments?
- mechanical strength
- positioning of organelles
- shape of a cell’s surface
Assign the cytoskeleton filament type to the according
diameter!
7 nm diameter: actin filaments
10 nm diameter: intermediate filaments
25 nm diameter: microtubules
Intermediate filaments form also a meshwork beneath the inner nuclear membrane called ?
Lamina
What are the functions of actin filaments?
- mechanical strength
- positioning of organelles
- shape of a cell’s surface
- whole-cell locomotion
How many staggered tetramers of two coiled-coil dimers form the intermediate filament?
8
In which type of intermediate filament are mutations responsible for the disease epidermolysis bullosa simplex (blistering of the skin in response to very slight mechanical stress).
Keratin
What is the morphology of intermediate filaments?
ropelike filaments
Growth of microtubules is controlled by ?
GTP hydrolysis
What are the functions of microtubules?
- mechanical strength
- intracellular transport
- cilia & flagella movement
- shape of a cell’s surface
- positioning of organelles
- formation of mitotic spindle
Microtubules grow out of an organizing structure called ?
Centrosome
Stable microtubules are a stiff support in cilia and flagella. Describe them
Cilia: generate a current and can be found in the respiratory tract and in cells of the oviduct wall.
Flagella: move the entire cell and can be found in sperm cells and protozoa.
What is the morphology of microtubules?
- hollow cylinders
Centrosomes contain a pair of ? And hundreds of nucleation sites.
Centrioles
Which end of the microtubule is protected by the
centrosome?
minus end
Dynein moves to the plus end and kinesin moves to the minus end?
False
The activity of actin filaments is influenced by extracellular signals. They lead to the activation of GTP-binding proteins of the Rho protein family.
Activation of Rac induces lamellipodia formation.
Activation of Cdc42 induces the formation of filopodia.
Activation of Rho results in the assembly of long bundles
All actin-dependent motor proteins belong to the?
Myosin family
The Z discs in sarcomeres are (direct) attachment sites for ..
Actin filaments
Myosin hydrolyzes ___ to provide energy for the movement along actin filaments.
ATP
Where are myosin I and Il expressed respectively?
Myosin I expressed in all cells.
Myosin Il expressed only in muscle cells.
Mention actin-binding proteins are responsible for cell locomotion?
- Spectrin
- ERM
- Filamin
What is the name of the spike-like projection of the plasma membrane that allow a cell to explore its environment (plural or singular)?
Filopodia
Which backbones can phospholipids have?
Sphingosin and glycerol
How are composed the membrane lipid molecules?
Hydrophilic head and hydrophobic tail
Membrane lipids are functionally important for cell signaling and apoptosis. One membrane lipid can only be found in the inner layer of cell membrane of living cells. In apoptotic cell ___________ translocates to the extracellular monolayer and the cell is phagocytosed
Phosphatidylserine
Which requirements have to fulfill the cellular membrane?
Cell signaling
Growth and motility
Transport
Barrier
Membrane lipids are_____, meaning they have hydrophilic and hydrophobic properties and are able to form bilayers spontaneously
amphiphilic
What can you say about membrane?
- A large of unsaturated hydrocarbon tails makes the membrane more fluid.
- The fluidity of a lipid bilayer depends on temperature and composition
-Lateral diffusion of lipids within the lipid layer can occurr
Which compartments are surrounded by two bilayers in eukariotic cells?
Nucleus and mitochondria
What are the most abundant membrane lipids?
Sterols, glycolipids and phospholipids
Which structures contain transmembrane proteins to cross the lipid bilayer?
Single pass alpha helix, rolled up beta sheet, multi pass alfa helices
The fluorescence based methods can be used to investigate the movement of membrane proteins. One method is based on the recovery after bleaching of the cell membrane with laser beam and is called _____ and the other method is based on continuous bleachin of the membrane called ______
FRAP and FLIP
Where are located the membrane associated, lipid anchored and protein associated membrane proteins?
Only one side of the cell membrane
Glycosylation of membrane proteins always occurs at the noncytosolic side of the membrane. If oligosacharide chains are linked to the proteins, ________ are generated, whereas the addition of polysaccharides to proteins results in the generation of ______
Glycoproteins and proteoglycans
Which of the following functions are fulfilled by the carbohydrate layer on the cell surface?
-Protection of cells against mechanical and chemical damage
-Assisting in cell-cell recognition and adhesion
-Keeping others cell distance
The GPI anchor is localized in the
Outer layer of the plasma membrane
Which molecules beginning with the one ehich can easily diffuse across the membrane:
Hydrophobic molecules
Small uncharged polar molecules
Large uncharged polar molecules
Ions
What can you say about passive transport
Charged molecules depend on electrochemical gradient
Water depend on a osmotic gradient
Uncharged molecules depend on a concentration gradient
Coupled transport can occur in 2 ways…
Antiport and symport
Which transport requires energy and moves solutes agains their concentration gradient?
Active
ATP-diven pumps hydrolyze
ATP to ADP
Membrane transport molecules fall in two clases:
Transporters, channel proteins, non membrane transport molecules: nucleoporins
Animal cells drive most transport processes across the membrane with electrochemical gradient of
Na+
What can you say about the Na+/K+ pump?
Is required for the osmotic balance of animal cells
Is driven by the transient addition of a phosphate group
Is crucial for the regulation of the cytosolic pH
Which stumili are able to open channels?
Voltage-gated
Mechanically gated
Mention some organelles and their function
Cytosol:many metabolic pathways
Endosome: sorting of endocytosis
Lysosome: intracellular degradation
Peroxisome: oxidation of toxins
Golgi apparatus: modification, sorting and packaging of proteins and lipids for secretion and deliver to another organels
Nucleus: genome, Dna and RNA synthesis
Rough endoplasmic : synthesis of most lipids and proteins for distribution
Mitochondrion: ATP synthesis by oxidative phosphorylation
What can you say about protein sorting signals?
Sorting signals are necessary for directing proteins towards their target organelles
Protein sorting signals are often removed aftter sorting
What can you say about the nuclear transport and PC?
Ran-GDP is localized in the cytosol
Small water soluble molecules are able to pass the pores non-selectively
Which statements about protein sorting are true?
There are different sorting signals for different cellular compartments
A typical sorting signal is required to direct a protein to its organelle
The sorting signal of proteins is a sequence of 15-60 aminoacids
What can you say about nuclear pores?
As nuclear pores are filled with water, small, water soluble mmolecules may pass non-selectively
During mitosis, the nuclear poe complexes disassemble
What is the function of the dephosphorylation of lamins in the nucleus during mitosis?
Induces reformation of the nuclear envelope around individual decondensing daughter chromosomes during early telophase
Which molecules are necessary for protein translocation across the ER membrane to occur?
Signal sequence, SRP, translocation channel, SP receptor
Proteins enter mitochondria unfolded. Chaperones pull them into the mitochondrial matrix and help with refolding?
True
What can you say about the ER and nucleus as membrane enclosed organelles?
The ER is the most extensive membrane in the eukaryotic cell
The outer membrane of the nucleus is continuous with the membrane of the ER
The ribosomes at the surface of the rough ER are synthesizing proteins
The rough endoplasmatic reticulum…
Has water soluble proteins in its lumen
Has prospective transmembrane proteins embedded in its membrane
Has ribosomes bound to the cytosolic side of its membrane
Harbors SRP receptors in its membrane
TOM complex…
Transfers proteins across the outer membrane
TIM complex…
Transfers proteins across the inner membrane
SAM complex…
Is a sorting and assembly machine and helps the TOM complex to transport proteins
What can you say about mitochondrial protein translocation?
The mitochondrial signal sequence found on precursor proteins is necessary for their localization to mitochondria
Chaperone proteins play a role in pulling proteins into the mitochondria and refolding
Where can you find the signal sequence in a protein which has to be sorted?
N-terminal
Why does the cell add oligosaccharides to proteins?
To add a transport signal
For protection from degradation
To retain proteins in ER until they are properly folded
Which proteins are involved in the process of budding clathrin coated vesicles?
Clathrin, adaptin, cargo molecule, cargo receptor, dynamin
Where are found the Rab proteins?
On the surface of vesicles
Where are expresses the tethering proteins?
On the cytosolic surface of the target membrane and recognize the Rab proteins
For what are required the SNARE proteins?
For the fusion of the vesicle with the target membrane
The regulation of vesicular transport events occurs via…
The use of different coat proteins
The specific expression of Rab and SNARE proteins
Different types of PIPs
What can you say about vesicle budding?
Budding of vesicles is driven by the assembly of a vesicle coat
Clathrin has the structure of a triskelion and is composed of heavy and light chains
Clathrin coated vesicles bud from the plasma membrane
Clathrin coated vesicles mediate transport from Golgi apparatus and from the plasma membrane?
True
COPI coated vesicles mediate transport from golgi apparatus and from the plasma memrane?
False
How is composed a clathrin?
36 triskelions, organized in a network of 12 pentagons and 6 hexagons. 3 heavy chaind and light chains
What can you say about coated vesicles?
They bind transmembrane receptors, bind coat proteins to the membrane, form a discrete inner layer of the coat
Materials des:ned for degrada:on follow 3 different pathways to the lysosome. Name
them
- autophagy
- endocytosis
- phagocytosis
Exocytosis is a regulated process for the delivery of lipids, proteins and carbohydrates to
the cell surface. What is the correct order for their fixed route?
- ER
- GOLGI
- vesicles
- plasma membrane
The Golgi apparatus is located near the nucleus. Bring the components of the Golgi in their correct order from the ER towards the cell membrane!
- cis Golgi network
- CIS cisternae
- medial cisternae
- trans cisternae
- trans Golgi network
What are the different main functions of phagocytosis?
- defense
- cleaning
- feeding
Secretory cells…
- produce large quantities of particular products
- produce vesicles which fuse with the plasma membrane after transmission of a
signal
-have a regulated exocytosis pathway
Endocvtosed macromolecules are sorted in endosomes and can have different fates.
During transcytosis…
the luminal content of a vesicle is transported via a recycling
endosome to a different domain of the plasma membrane.
What can you say about autophagy and the formattion of autophagosomes?
- mTOR complex 1 signals to the autophagic machinery.
- Acid hydrolases are digesting the inner membrane and luminal contents.
- Autophagosomes fuse with lysosomes, catalyzed by SNAREs.
Small GTPases, large GTPases, and G-proteins have intrinsic ____?____activity.
GTP hydrolyzing
What is true about signaling by protein phosphorylation?
-Protein kinases are frequently organized in a cascade
-Phosphate residues are attached to serine, threonine and tyrosine
-Dephosphorylation events are reversible
-Ser/ thr kinases phosphorlyate serines and threonin
A sequence of two inhibitory signals produces a secured negative signal.
False
Mention four styles of cell communication to their appropriate explanation in layman’s terms
phone call or e-mail: neuronal signaling
Face to face conversation: contact dependent
Broadcast over ratio station: endocrine signaling
Post a flyer on selective notice boards:paracrine signals
Small monomeric GTPases are regulated by …
GAPS: inactivate the protein
GEFS: activate the proteins
Enzyme coupled receptors
-can associate directly with enzymes that they activate
-Activates enzymes via G proteins
-Can function as enzymes
A trimeric GTP-binding protein mediates the interaction between the activated G-protein-coupled receptor and its target protein. These receptors generally target enzymes or chaperones in the cytosol.
False
What can you say about intracellular signaling complexes?
Some activated receptors phosphorylate phosphoinositides, whereby intracellular signaling proteins can bind
A GPCR signal is shut off by…
-the hydrolysis of the GTP bound to the a-subunit
What can you say about G-protein coupled receptors (GPCRs) and G-proteins are true?
-GPCRs represent the largest family of cell surface receptors.
-The extracellular domain of the GPCR binds to the ligand whereas the intracellular domain is coupled to the G-protein.
-GDP is bound to the a-subunit of the G-protein in its inactive state.
-GPs are seven-pass transmembrane receptors.
Ion channels are targets of GPCRs. Which of the following statements are true?
-The activated G-protein opens K+ channels in the plasma membrane of heart muscle cells.
-Acetvlcholine binds to GPCRs on the cell surface of heart muscle cells.
-The outflow of K+ into the extracellular space decreases the excitability of the cell.
Which subunits of a G-protein are tethered to the membrane by lipid tails?
-alpha-subunit
-gamma-subunit
The cholera toxin modifies GPCR signaling. It causes __________ via the GPRC resulting in water loss.
continuous signaling
The GTPase domain of the a subunit contains two major subdomains:
Ras domain, which is related to other GTPases and provides one face of the nucleotide-binding pocket and the AH domain, which clamps the nucleotide in place.
Activation of a G-protein leads to its complete dissociation into its alpha-, gamma- and beta-subunits, which subsequently interact with their targets, respectively.
FALSE
What leads to the inactivation of an alpha-subunit of a G-protein?
alpha-subunit hydrolyzes its bound GTP
Receptor tyrosine kinases (RTK) activate a cascade which results in the activation of ERK. Please bring them in the correct order starting with the protein directly downstream of the RTK!
- Ras
- Raf
- MEK
The PI3K-AKT signaling pathway regulates…
-cell growth
-survival
Receptor tyrosine kinases…
-contain intracellular binding sites for adaptors.
-dimerize upon binding of a ligand.
-harbor tyrosine residues which can be phosphorylated.
Enzyme coupled receptors…
-play a major role in cell growth, survival, and proliferation.
-are transmembrane proteins.
-are enzymes themselves or in complex with enzymes.
-transmit signals.
What can you say about Bad protein and Akt?
-Phosphorylation of Bad leads to its inactivation.
-Apoptosis-inhibitory proteins are inactive if they are bound to Bad.
The phosphorylation of phosphatidylinositol (PI) on the carbon atom 3 diverts the molecule away from the pathway leading to IP3 and diacylglycerol.
True
What activates Cdks?
-Phosphorylation by CAK
-Binding of cyclin
During mitosis, a cell can still pause before a specific transition point. But once it has passed this point, the cell carries on to the end of mitosis. What is this transition called?
-metaphase-to-anaphase transition
Mention the phases and roles of mitosis
- Condensation of replicated chromosome and assembly of mitotic spindle: Prophase
- Breakdown of the nuclear envelope and attachment of kinetochores to spindle microtubules: Prometaphase
- Alignment of chromosomes at the equator: Metaphase
Separation of sister chromatids and movement toward the spindle pole they face: Anaphase - Decondensation of daughter chromosomes and reassembly of new nuclear envelope: Telophase
- Division of the cytoplasm by a contractile ring: Cytokinesis
What happens during the cell cycle, if extracellular conditions are unfavorable?
Cells may enter the resting state GO
The contractile ring during the cytokinesis is composed of actin and myosin I.
False
What can be said about Cdks?
-Cyclins are regulators of Cdks
- Are important components of the cell-cycle control system
The cell cycle has three major check points:
- Before entering mitosis: G2/M Transition
- Before entering the last phases of mitosis and proceeding to cytokinesis: Metaphase-to-anaphase
- Before entering cell cycle and proceeding to S phase: Start Transition
The contractile ring during the cytokinesis is controlled by the RhoA. Which protein leads to its deactivation?
RhoGAP
Sister chromatid cohesion depends on a large protein complex called _______
It contains ATPase domains which are required for its loading on the DNA
cohesin
Which statements about cancer are true?
-Cancer cells can modify the extracellular matrix.
-Cancer cells usually lost contact inhibition.
In normal tissue the total cell amount remains stable. This state is called homeostasis.
For this reason, both increased ________ and decreased ________ can contribute to tumorigenesis.
cell division - apoptosis
Which statements about meiosis are true?
-It produces haploid cells.
-Consists of two divisions.
Damaged DNA has to be repaired before the cell enters the S phase or M phase. What can you say about DNA damage?
- p53 activates transcription of p21
- Protein kinases called ATM and ATR are activated
Development of cancer requires a spontaneous mutation which directly leads to uncontrolled proliferation and invasive behavior.
False
Abnormal activity of Ras or Myc would induce excessive stimulation of mitogenic pathways. Normal cells react with the activation of …
Arf thereby increases p53 levels
What do mitogens stimulate?
-cell division
