CH 9
Cell Signaling
Cell Signaling
What are the four essential elements of cell communication?y
Signaling cell, signaling molecule, receptor molecule, and responding cell
What is the cytoskeleton’s main role in cells (2)?
To provide internal structural support and enable the movement of materials within the cell
What are the two main phases of the eukaryotic cell cycle and what are their purposes?
Interphase prepares the cell for division which includes DNA replication; M phase divides the cell
What are the five stages of mitosis in order?
Prophase, Prometaphase, Metaphase, Anaphase, Telophase
What are the three main DNA repair mechanisms?
Post-replication mismatch repair, base excision repair, and nucleotide excision repair
What type of signaling involves molecules traveling through the bloodstream to reach distant cells?
Endocrine Signaling
Which cytoskeletal filament is made of tubulin dimers?
Microtubules
Explain what Okazaki fragments are and why they must be produced
DNA polymerase can only add nucleotides in the 5′–3′ direction, so the lagging strand must be built in short, discontinuous fragments.
What is the role of kinetochores during mitosis?
To attach chromosomes to spindle microtubules
What is the difference between a non-synonymous and synonymous mutation?
Non-synonymous changes the amino acid; synonymous does not - due to how every codon has one amino acid it codes for, but multiple codons code for the same amino acid
Why do polar and non-polar signaling molecules use different types of receptors and what are those receptors?
Polar molecules can’t pass through the lipid membrane so bind surface receptors; non-polar molecules can diffuse through to bind intracellular receptors
What property of actin filaments allows cells to move or change shape quickly?
Their dynamic polymerization and depolymerization at the plus and minus ends
Describe the difference in DNA replication between prokaryotic DNA and eukaryotic DNA
Prokaryotic DNA which is circular has one origin of replication; eukaryotic chromosomes have many origins to replicate large genomes efficiently
What are cyclins and CDKs, and what is their function?
Cyclins, which are synthesized and degraded cyclically, activate CDKs, which are always present; together they regulate progression through the cell cycle
Why are most mutations neutral in humans?
Only ~2.5% of the human genome codes for proteins, so most mutations occur in noncoding regions
Explain, very simply, phosphorylation and its role in signaling pathways
Kinases add phosphate groups to activate proteins; phosphatases remove them to deactivate proteins, controlling the pathway’s on/off state
Explain how cadherins and integrins work and include where each are used
Cadherins, found in adherens junctions and desmosomes, connect cells to cells by the cytoplasmic domain attaching to microfilaments and the extracellular domains attaching to one another; integrins (integrin dimer), found in hemidesmosomes, connect cells to extracellular matrix for structural integrity under stress at the surface of most animal cells
Name four proteins involved in DNA replication and their role
Topoisomerase II; helicase; DNA polymerase; RNA primase; DNA ligase; telomerase
Explain the role of p53
p53, as the guardian angel of the genome, detects DNA damage and can halt the cell cycle or trigger apoptosis to prevent passing on mutations - tumor suppressor
Explain the ways that somatic and germ-line mutations differ
Somatic mutations occur in body cells, aren’t inherited, and are less tightly regulated; germ-line mutations occur in reproductive cells, can be passed to offspring, and are more strictly controlled to prevent heritable errors
A mutation in a receptor prevents GTP from hydrolyzing back to GDP. What effect would this have on the cell?
The G protein would remain permanently active, leading to continuous signaling/uncontrolled activation
Why would a mutation in keratin genes cause the disease epidermolysis bullosa?
Keratins are intermediate filaments that provide mechanical strength to skin; without them, cells tear under stress
Explain the role and telomeres and how they solve a problem for linear DNA
Telomeres, repetitive, non-coding sequences at the end of linear DNA, protect chromosome ends and prevent loss of DNA during replication on the lagging strand, since the removal of the RNA primer leaves coding DNA not replicated; a telomerase with an RNA template codes for additional telomere repeats which then allows a new segment of the lagging strand to be formed
How do mutations in two specific genes collectively lead to cancer?
Each mutation removes a layer of control, proto-oncogene mutations promote overactive division, and tumor suppressor genes' mutation removes division inhibition, together enabling uncontrolled growth.
How does Cystic Fibrosis occur?
An in-frame deletion (one full amino acid deleted) causes a misfolded protein that affects secretions in many organs; the CFTR gene is affected which is meant to pump chloride ions out of the cell