Molecular Biology: Gene Expression and Function

Control of Gene Expression

• Different cell types arise from the same genome through selective gene expression.
• Transcription is the most common and efficient stage for regulating gene expression.
• Regulatory proteins control cell differentiation by activating tissue-specific genes.
• Oct4, Sox2, and Klf4 are transcription factors required for reprogramming differentiated cells into pluripotent stem cells (iPS cells).

Analyzing the Structure and Function of Genes

• PCR amplifies specific DNA sequences for molecular cloning and diagnostics.
• Sanger sequencing determines nucleotide order by using dideoxynucleotides.
• Restriction enzymes cut DNA at specific sites to create recombinant plasmids.
• Reporter genes are linked to regulatory sequences to monitor gene expression.
• GFP is a commonly used reporter gene that fluoresces under certain conditions.

How Cells Obtain Energy from Food

• Most ATP is generated in mitochondria through oxidative phosphorylation.
• Glycolysis occurs in the cytosol, converting glucose to pyruvate.
• Pyruvate is converted to acetyl-CoA in the mitochondrial matrix.
• The TCA cycle takes place in the mitochondrial matrix.
• During fermentation in muscle cells, pyruvate is reduced to lactate, producing 2 ATP per glucose.
• Fermentation in yeast converts pyruvate to ethanol and CO2, also producing 2 ATP per glucose.
• Fatty acids are broken down into acetyl-CoA through β-oxidation, which enters the TCA cycle for energy production.
• Amino acids can be converted to intermediates that enter the TCA cycle for energy production.

Energy Generation in Mitochondria and Chloroplasts

• A proton gradient is generated across the mitochondrial inner membrane during the electron transport chain, driving ATP synthesis.
• ATP synthase uses the proton gradient to synthesize ATP during oxidative phosphorylation.
• Mitochondria have a double membrane with the inner membrane folded into cristae.
• Chloroplasts contain thylakoid membranes (site of light reactions) and stroma (site of the Calvin cycle).
• Muscle and sperm cells have more mitochondria because they have high energy demands.
• Acetyl-CoA plays a central role in both catabolism (TCA cycle) and anabolism (lipid biosynthesis).
• Oxygen is the final electron acceptor in the electron transport chain, allowing for efficient ATP production.
• In mitochondria, ATP is directly transported to the cytosol for cellular use.
• In chloroplasts, ATP is used within the chloroplast to synthesize carbohydrates.
• Photosystem II occurs first, producing O2 and ATP, followed by Photosystem I, which produces NADPH.
• The Calvin cycle consumes 9 ATP and 6 NADPH in each turn.
• The main product of the Calvin cycle is glyceraldehyde 3-phosphate (G3P), which is used to form glucose and other carbohydrates.

Membrane Structure

• Membrane organelles include the nucleus, ER, Golgi apparatus, and mitochondria.
• Phosphatidylcholine is the most abundant phospholipid in the cell membrane.
• Cholesterol helps modulate membrane fluidity by providing membrane stiffness.
• Lipid synthesis occurs in the smooth ER, with enzymes like scramblase and flippase facilitating lipid distribution between membrane leaflets.
• Membranes are asymmetric, with different lipid compositions on the inner and outer leaflets.
• Membrane proteins include transporters, anchors, receptors, and enzymes, each facilitating specific cellular functions.