UNIT 3

die

Glycolysis

The process by which glucose is broken down into pyruvate, yielding 2 ATP molecules and 2 NADH in the cytoplasm.

Krebs Cycle (Citric Acid Cycle)

A series of reactions in the mitochondrial matrix that produces ATP, NADH, FADH₂, and CO₂ by oxidizing acetyl-CoA.

Oxidative Phosphorylation

The production of ATP using the energy derived from redox reactions in the ETC, resulting in a proton gradient that drives ATP synthesis.

NADH

An electron carrier produced in glycolysis, acetyl-CoA formation, and the Krebs cycle, donating electrons to the ETC.

FADH₂

An electron carrier produced in the Krebs cycle, donating electrons to the ETC but yielding less ATP than NADH.

Proton Gradient

A concentration difference of protons across the mitochondrial inner membrane, driving ATP synthesis through chemiosmosis.

Chemiosmosis

The movement of protons across the mitochondrial membrane, driving the synthesis of ATP by ATP synthase in the ETC.

DNA (Deoxyribonucleic Acid)

The molecule carrying genetic information, composed of two complementary strands forming a double helix, made up of nucleotides (adenine, thymine, cytosine, guanine).

Nucleotide

The basic unit of DNA, consisting of a sugar (deoxyribose), a phosphate group, and a nitrogenous base (A, T, C, or G).

Double Helix

The twisted-ladder structure of DNA, with complementary base pairs (A-T, C-G) forming the "rungs" and the sugar-phosphate backbone forming the "sides."

Base Pairing Rules

Adenine pairs with thymine (A-T) and cytosine pairs with guanine (C-G) through hydrogen bonding, maintaining a uniform DNA structure.

Hydrogen Bonds in DNA

Weak bonds between complementary bases that hold the two DNA strands together; two bonds between A-T pairs and three between C-G pairs.

DNA Replication

The process of copying DNA, occurring in the S phase of the cell cycle, where each strand serves as a template for a new complementary strand.

Helicase

An enzyme that unwinds the DNA double helix at the replication fork, separating the two strands for replication.

Leading Strand

The DNA strand that is synthesized continuously toward the replication fork by DNA polymerase during replication.

Lagging Strand

The DNA strand that is synthesized discontinuously in short fragments (Okazaki fragments) away from the replication fork, later joined by DNA ligase.

Okazaki Fragments

Short DNA fragments synthesized on the lagging strand during DNA replication, which are later joined by DNA ligase.

Semi-Conservative Replication

The model of DNA replication in which each new DNA molecule consists of one original strand and one newly synthesized strand.

Cell Cycle

The series of stages a cell goes through to grow and divide, consisting of interphase (G1, S, G2) and mitotic phase (mitosis and cytokinesis).

Interphase

The phase where a cell spends most of its life, consisting of G1 (cell growth), S (DNA replication), and G2 (preparation for mitosis).

G1 Phase

The first growth phase in interphase, where the cell grows, produces organelles, and synthesizes proteins necessary for DNA replication.

S Phase

The synthesis phase in interphase, where DNA is replicated, resulting in two identical sets of chromosomes.

G2 Phase

The second growth phase in interphase, where the cell continues to grow, checks for DNA errors, and prepares for mitosis.

Mitosis

The division of a cell's nucleus into two identical nuclei, ensuring each daughter cell receives an identical set of chromosomes.

Cytokinesis

The division of the cytoplasm, resulting in two separate daughter cells with their own nuclei and organelles.

Checkpoints in Cell Cycle

Regulatory points (G1, G2, M checkpoints) where the cell assesses conditions to ensure accurate progression through the cycle.

G1 Checkpoint

Ensures the cell is ready for DNA replication, checking for adequate size, nutrient supply, and DNA integrity.

G2 Checkpoint

Checks for DNA damage after replication and ensures all DNA has been accurately replicated before mitosis.

M Checkpoint (Spindle Checkpoint)

Ensures chromosomes are correctly attached to the spindle apparatus, allowing for equal chromosome separation during mitosis.

Apoptosis

Programmed cell death, a mechanism to eliminate damaged or unneeded cells, often activated if cell cycle errors cannot be corrected.

Cancer and the Cell Cycle

Uncontrolled cell division due to loss of cell cycle regulation, often caused by mutations in genes controlling checkpoints.

Cyclins

Proteins that regulate the cell cycle by activating cyclin-dependent kinases (CDKs), essential for cell cycle progression.

Cyclin-Dependent Kinases (CDKs)

Enzymes that, when bound to cyclins, phosphorylate target proteins to push the cell through each phase of the cycle.

Tumor Suppressor Genes

Genes that produce proteins to prevent uncontrolled cell growth; mutations in these genes can lead to cancer.

Proto-Oncogenes

Genes that, when mutated, become oncogenes and can cause cells to divide uncontrollably, contributing to cancer development.

p53 Protein

A tumor suppressor protein that can halt the cell cycle at the G1 checkpoint if DNA damage is detected, allowing for repair or apoptosis.

Density-Dependent Inhibition

A property in which crowded cells stop dividing; often lost in cancerous cells.

Anchorage Dependence

The requirement that cells must be attached to a substratum to divide, a feature often absent in cancer cells.

Metastasis

The spread of cancer cells from their original site to other parts of the body, forming secondary tumors.

Acetyl-CoA Formation

The process following glycolysis where pyruvate is converted to acetyl-CoA, releasing CO₂ and forming NADH.

Electron Transport Chain (ETC)

A series of proteins in the mitochondrial membrane that transfer electrons, releasing energy to pump protons and generate ATP.

ATP Synthase

An enzyme in the mitochondrial membrane that synthesizes ATP as protons flow back into the matrix, driven by the proton gradient.

NADH and FADH₂

Electron carriers that transfer electrons to the ETC, powering ATP production in oxidative phosphorylation.

Anaerobic Respiration

Cellular respiration occurring without oxygen, resulting in the production of lactic acid or ethanol and significantly less ATP.

Fermentation

A type of anaerobic respiration that generates ATP by converting glucose into lactic acid or ethanol when oxygen is unavailable.

Lactic Acid Fermentation

The process where glucose is converted to lactate in muscle cells during anaerobic conditions, regenerating NAD⁺ for glycolysis.

Alcohol Fermentation

A process in yeast and some bacteria where glucose is converted to ethanol and CO₂, regenerating NAD⁺ for glycolysis.

Semiconservative Replication

The process by which each new DNA molecule contains one original strand and one newly synthesized strand.

DNA Polymerase

An enzyme that synthesizes new DNA strands by adding nucleotides to the 3' end of an existing strand during replication.

Leading Strand

The continuously synthesized strand of DNA during replication, moving towards the replication fork.

Lagging Strand

The DNA strand synthesized discontinuously in short segments (Okazaki fragments), moving away from the replication fork.

Okazaki Fragments

Short DNA fragments formed on the lagging strand during DNA replication, later joined by DNA ligase.

DNA Ligase

An enzyme that joins Okazaki fragments on the lagging strand, creating a continuous DNA strand.

Helicase

An enzyme that unwinds the DNA double helix at the replication fork, allowing each strand to be copied.

Primase

An enzyme that synthesizes RNA primers, providing a starting point for DNA polymerase during replication.

Single-Strand Binding Proteins (SSBs)

Proteins that stabilize the unwound DNA strands, preventing them from re-forming a double helix during replication.

Topoisomerase

An enzyme that relieves the strain caused by the unwinding of DNA by cutting and rejoining the strands ahead of the replication fork.

ATP

The primary energy carrier in cells, consisting of adenine, ribose, and three phosphate groups. Energy is released when a phosphate group is removed to form ADP.