Cell Cycle Flashcards
What does DNA ligase do?
Seals together Okazaki fragments on the lagging strand
Which direction does DNA polymerase work?
Reads DNA 3’ to 5’. New strand grows 5’ to 3’.
What does interphase consist of?
G1 - cell content replication and growth.
S - DNA replication.
G2 - more growth.
What’s the function of helicase?
To unwind the DNA double helix and separate the strands.
What is an exonuclease?
An enzyme that cleaves nucleotides (one at a time) from the end of a polynucleotide chain.
What happens in G0?
G0 is when the cell cycle is arrested (non dividing) and the cell is in a distinct quiescent state, but still metabolically active
What is the nucleolus?
Small dense structure within the nucleus made up of proteins and RNA responsible for making ribosomes
What is synapsis?
the pairing of two homologous chromosomes that occurs during meiosis. It allows matching-up of homologous pairs prior to their segregation, and possible chromosomal crossover between them.
What is the SRY gene?
The sex-determining region Y. Protein produced acts as a transcription factor. This protein starts processes that cause a fetus to develop male gonads (testes) and prevent the development of female reproductive structures (uterus and fallopian tubes).
What does aneuploidy of germline cells have less effect than on somatic cells?
Would only affect sexual characteristics (genes on X and Y chromosomes), normal growth and genes and proteins will still develop
What is xeroderma pigmentosa?
Autosomal recessive defect in nucleotide excision repair enzymes are mutated - reduction in NER. Therefore, damage to cells caused by UV light (pyrimidine dimers) cannot be repaired.
What are common targets of anti-cancer agents?
Damage enzymes involved in DNA replication therefore can’t replicate and divide
Damage manipulation of DNA - topoisomerases - affect untangling if DNA
Mutant bases - cannot be replicated
Prevent nucleotide production- nothing to be incoooerated
Damage DNA itself (radiation) can’t be
What is non homologous end joining?
Two double strand breaks are ligated without need for homologous template. Repairs close by pieces of DNA, ligates then together
Mechanism to protect the ds ends from endonuceases
What is the potential problem with non homologous end joining?
Too many DSB, problem with non homologous, quick process, doesn’t look for matching DNA, could match any ends together- cause DNA inappropriate joins.
How long does spermatogenesis take?
~ 60 days
What is senescence?
Permanent cell cycle arrest
What is INTRA-tumour heterogeneity?
Different sub-clones within the SAME TUMOUR
What are the features of an alpha helix? (3)
3.6 aa / turn
0.54nm pitch
Right-handed helix
What is a motif?
folding patterns containing 1 or more elements of secondary structure
What is a domain?
part of a polypeptide chain that fold into a distinct shape. Often has a specific functional role
What are amyloidoses?
disorders of protein conformation and metabolism in which insoluble fibrils are deposited in body organs
Recombination frequency between two linked genes is dependent on ____________________
How close together they are on the chromosome
Genes close together on the chromosome are said to be __________ linked
Tightly
Where are proteins targeted to the nucleus, mitochondria and peroxisomes translated?
Cytosolic free ribosomes
What is the peroxisomes targeting sequence?
A sequence of serine – lysine – leucine usually present on the C-terminus
What receptor recognises PTS?
Pex5
What enables peroxisomes targeted proteins bound to Pex5 to enter peroxisomes?
15 pex proteins make up a transport channel across the peroxisomal membrane
Does peroxisomes protein targeting require energy?
Yes, ATP hydrolysis needed for recycling of the PTS receptor
What is Zellweger syndrome an example of?
A peroxisome biogenesis disorder
What do endocrine cells secrete?
Hormones, into the bloodstream (without ducts)
What do exocrine cells secrete?
Secrete digestive enzymes (often) into ducts
What is the signal sequence for secretory proteins?
N-terminal aa sequence of 5- 30 amino acids that are rich in hydrophobic residues - Able to form an alpha helix
What receptor recognises the signal sequence of proteins destined for the ER?
Signal recognition peptide (SRP)
What enzyme in the ER membrane cleave the signal sequence from the protein?
Signal peptidase
Name 5 functions of the ER
Insertion of proteins into membranes Specific proteolytic cleavage N linked Glycosylation Formation of disulphide bonds Assembly of multisubunit proteins Hydroxylation of selected lysine and proline residues
In N linked glycosylation where are sugars added?
Onto an asparagine side chain
What protein forms disulphide binds in the ER?
protein disulphide isomerase (PDI)
What proteins attempt of correct misfolding of proteins in the ER?
ER chaperone proteins
Where does the sugar attach to in O linked glycosylation?
Attaches to the OH group of serine or threonine. Occurs in Golgi
90% of all body collagen (skin, tendons, ligaments, bone) is what type?
Type 1 - a1(x2), a2 (x1)
What is scurvy due to?
Well triple tropocollagen helices
What does iron bind to in haemoglobin and myoglobin?
The proximal histidine
What two things are long term regulators of enzyme activity?
- Change in rate of protein synthesis
2. Change in rate of protein degradation
Why is protein phosphorylation so effective?
It adds 2 negative charges (from phosphate) which make H-bonds
Allows for amplification effects
What are the 4 basic steps of gene cloning?
Isolate relevant gene using restriction enzymes
Insert gene into plasmid vector (recombinant DNA)
Introduce recombinant DNA molecule into suitable host cells e.g. E. coli
Identify and isolate the clone containing the DNA of interest
How would you identify proteins? (Proteomics)
Digest protein with trypsin
Perform mass spectrometry
Generate list of peptide sizes
Use database of predicted peptide sizes for known proteins to Identify protein
What are polyclonal antibodies?
Produced by many B lymphocytes include multiple different antibodies that are specific to 1 antigen (multiple epitope)
What are monoclonal antibodies?
Produced from 1 B lymphocyte produce identical antibodies (same epitope) - specific to 1 antigen
Give two examples of continuous enzyme assays
Spectrophotometry
Chemoluminescence
Give two examples of discontinuous enzyme assays
Radioactivity
Chromatography
What method is used for diagnosis of MI?
measurement of cardiac troponin I by ELISA
