Biology Exam 1: Cell Membrane Proteins

Exam 1

Proteins associated with the lipid bilayer:
- Integral proteins are embedded within the lipid bilayer, with a hydrophobic affinity.
- Peripheral proteins are on the membrane surface, with a hydrophilic affinity.
- Lipid-anchored proteins are on the membrane surface, covalently bound to hydrophilic molecules.
- Integral proteins can be classified as monotopic, single-pass, multipass, or multi-subunit proteins.
- Peripheral proteins are bound by electrostatic forces or hydrogen bonds.
- Lipid-anchored proteins are covalently attached to lipid molecules embedded in the bilayer (e.g., fatty acid or isoprenyl anchors on the inner surface or GPI anchor on the outer surface).
Phospholipid structure and fluidity: -Phospholipids have a structure with two fatty acid tails and a phosphate head.
- Features that increase fluidity include shorter fatty acid tails and higher levels of unsaturated fatty acids.
- Features that decrease fluidity include longer fatty acid tails and higher levels of saturated fatty acids.
Primary classes of lipids in cell membranes:
- Phospholipids
- Glycolipids
- Sterols
Fluid mosaic model:
- Proposed by Singer and Nicolson.
- Explains the structure of cell membranes as a fluid mixture of lipids and proteins.
Glycolysis:
- Breakdown of glucose to pyruvate.
- Rate-limiting steps include:
  - Hexokinase (step 1)
  - Phosphofructokinase (step 3)
  - Pyruvate kinase (step 10)
- Purpose is to produce ATP.
Products of glycolysis:
- Under aerobic conditions, the products of glycolysis enter the citric acid cycle.
- Under anaerobic conditions, fermentation occurs to create lactic acid or alcohol.
Transcription:
- The process of converting DNA to pre-mRNA.
- Four phases: initiation, elongation, and termination.

Exam 2

Rough ER:
- Contains ribosomes.
- Found near the nucleus.
- Synthesizes proteins.
- Composed of cisternae.
Smooth ER:
- Lacks ribosomes.
- Synthesizes lipids (e.g., testosterone, estrogen).
- Composed of tubules.
- Often found near the cell membrane.
Protein insertion into Rough ER:
- Proteins are targeted to ER by signal sequences, bound by SRP and SRP receptor, inserted into the ER membrane.
- Type I: N terminal cytosolic and C terminal ER lumen
- Type II: N terminal ER lumen and C terminal cytosolic
- Type IV: Multiple transmembrane segments
Glycosylation:
- Adds carbohydrate groups to proteins.
- Aids in protein sorting, aids in disulfide bond formation, and quality control.
Transport across the lipid membrane (channels vs. transporters):
- Channels transport water, ions, and small hydrophilic molecules passively.
- Transporters transport a wider variety of molecules actively or passively.

Exam 3

Cytoskeletal structures:
- Microfilaments:
  - Made of actin.
  - Increase surface area, aid in cell movement, and provide structural support.
  - Form structures like microvilli, lamellipodia, filopodia.
- Microtubules:
  - Made of tubulin.
  - Important for cell function, polarity, and dynamic instability.
  - Essential for cell division (spindle fibres), intracellular transport, and maintaining cell shape.
- Intermediate filaments:
  - Provide strength for tissues and cells.
  - Rope-like, structural components in a variety of cell types.

Exam 4 and 5

Structure and direction of movement of kinesins and dyneins: - Kinesins move cargo toward the (+) end. - Dyneins move cargo toward the (-) end.
Types of junctions: - Anchoring junctions (cadherins and desmosomes) enable cell to function as a unit. - Tight junctions (occludin and claudin) prevent the movement of molecules across cell layers. - Gap junctions (connexins) allow direct communication between cells.
DNA binding domains:
- Examples include homeodomain, zinc-finger, leucine zipper, and basic helix-loop-helix.
- These domains bind to DNA to regulate gene expression.
Epigenetic regulation: Includes DNA methylation, histone modifications and non-coding RNA-mediated mechanisms that modify gene expression without altering the DNA sequence.
CDK cyclin complex regulation: involved in driving the cell cycle via phosphorylation of substrates. Various cyclin–CDK complexes carry out different regulatory functions at various stages of the cell cycle.

Exam 6, 7, and 8

Cell cycle checkpoints:
- Anaphase-promoting complex (APC) and Mitotic spindle checkpoint:
  - Ensure proper chromosome segregation before cell division.
- G1 Cdk-cyclin checkpoint:
  - Regulates the progression through the cell cycle.
- DNA damage checkpoint:
  - Involves p53 activation to halt the cycle/induce apoptosis as a response to damage.
Cancer causes and development:
- Carcinogens, genetic predisposition.
- Ames test (testing for mutagenicity).
- Categories of cancer (carcinomas, sarcomas, lymphomas, leukemias)
- Benign vs. malignant tumors
- Tumor initiation, progression and clonal selection.
- Loss of contact inhibition.
- Viral origins of oncogenes.
- RAS study using transfected cells and injections into mice.
- Gene mutations that regulate cell growth (e.g., Ras).
- Tumor suppressor genes (e.g., Rb, APC, p53).
- Risk factors (age, inherited mutations, viruses, exposure to radiation, obesity).

Exam 9 and 10

Molecular approaches to cancer: early detection (screening), surgical approaches (preventive, diagnostic, curative), hormone therapy, radiation therapy, chemotherapy.
Environmental chemicals and cancer risk: Polychlorinated biphenyls, dioxins, chromium, asbestos, chlorofluorocarbons. Persistence of chemicals.