Cell Types, Size and Shape Adaptations

• Scientists group cells by DNA location (nucleus or not), size, shape, presence/absence of membrane-bound organelles, and whether they are prokaryotic or eukaryotic

Types of Cells

• The two basic types are prokaryotic and eukaryotic

Human Cells

• All human cells (except red blood cells) have a nucleus, cell membrane, cytoplasm, and organelles for essential functions
• They all contain DNA and perform metabolic activities to sustain life

Cell Shape and Size Adaptations

• Nerve cells (neurons) feature long extensions (axons) as an adaptation that helps transmit electrical signals over long distances
• Muscle cells are long and fibrous to allow contraction and movement
• Blood cells are small and flexible to move through narrow blood vessels and efficiently carry oxygen

Importance of Cell Shape and Size to Function

• Red blood cells are small and round to maximize oxygen transport through blood vessels
• Nerve cells have long extensions for rapid communication
• Muscle cells are elongated to contract and generate movement

Interphase

• Interphase is when the cell grows, replicates its DNA, and produces necessary proteins and organelles to prepare for mitosis

Stages of Mitosis and Cytokinesis

• Interphase: The cell grows, replicates DNA, and prepares for mitosis
• Prophase: Chromatin condenses into chromosomes, the nuclear membrane breaks down, and spindle fibers form
• Metaphase: Chromosomes line up at the center (equatorial plate) of the cell
• Anaphase: Sister chromatids are pulled apart to opposite ends of the cell
• Telophase: Two new nuclear membranes form around the separated chromatids, which now become chromatin again
• Cytokinesis: The cytoplasm divides fully, splitting the parent cell into two daughter cells

Mitosis

• Mitosis ensures identical daughter cells by precisely copying DNA during interphase and evenly distributing the duplicated chromosomes into two nuclei
• Accurate separation of sister chromatids guarantees that each daughter cell receives an exact copy of the original genetic material

Reproduction

• Sexual Reproduction: Requires two parents who contribute gametes (sperm and egg), resulting in genetically diverse offspring due to recombination and independent assortment
• Asexual Reproduction: Involves only one parent, and offspring are genetically identical clones of the parent; this occurs in organisms like bacteria, plants, and some animals

Binary Fission vs. Mitosis

• Binary Fission occurs in prokaryotic cells (like bacteria), where the single circular DNA molecule replicates, and the cell simply splits into two
• Mitosis occurs in eukaryotic cells, where multiple linear chromosomes are replicated, organized and pulled apart using spindle fibers before cell division

Diversity in Reproduction

• Sexual Reproduction increases genetic diversity because it involves recombination of genes from two parents

Chromatin, Chromatid and Chromosomes

• Chromatin is the loose, uncoiled form of DNA and proteins found in the nucleus
• A chromosome is a condensed, tightly coiled structure of DNA that forms before cell division
• A chromatid is one half of a duplicated chromosome; sister chromatids are identical copies joined by a centromere before being separated during mitosis

Cell Cycle

• Interphase is the longest phase, taking up most of the cell cycle as the cell grows and prepares for division

DNA

• DNA carries genetic instructions for building proteins, which determine cell function, structure, and inherited traits

Experiments Determining DNA as Genetic Material

• Griffith Experiment: Griffith discovered the “transforming principle” when he observed that harmless R-Bacteria became deadly when mixed with heat-killed S Bacteria; this suggested that genetic material was transferred, but he didn’t determine if it was DNA or Protein
• Avery Experiment: Avery continued Griffith’s work, using enzymes to destroy proteins, RNA and DNA; when DNA was destroyed, transformation didn’t occur, proving that DNA - not protein - was the genetic material
• Hershey & Chase Experiment: Hershey and Chase used radioactive labeling to track whether DNA or Protein was injected into bacteria by viruses; only radioactive phosphorus (found in DNA) entered the cells, proving that DNA - not protein - is the hereditary material

DNA Extraction Lab

• Detergent dissolves the cell membrane and nuclear membrane, allowing the DNA to be released from the cell
• Enzymes break down proteins and other cellular components that are bound to the DNA, helping to free and purify the DNA
• Alcohol precipitates the DNA, causing it to clump together and become visible, making it easier to extract

Gene Expression

• Cells can have the same DNA but different structures and functions because different genes are turned on off in different cell types
• This process, called gene expression, allows specialized cells (such as muscle cells, nerve cells, and skin cells) to perform distinct functions despite having the same genetic information

Chromosomes

• Humans have 46 chromosomes in each of their somatic (body) cells, arranged in 23 pairs
• Human gametes (sperm and egg cells) contain 23 chromosomes each

DNA Components

• The monomer of DNA is a nucleotide, which consists of a phosphate group, a deoxyribose sugar, and a nitrogenous base
• The four nitrogenous bases that make up DNA nucleotides are Adenine (A), Thymine (T), Cytosine (C), and Guanine (G)
• The bonds that hold base pairs together are hydrogen bonds, and these bonds are relatively weak compared to covalent bonds, allowing the DNA strands to separate during replication and transcription

Cells are grouped by DNA location, size, shape, and membrane-bound organelles. The two basic types are prokaryotic and eukaryotic. Human cells have a nucleus, cell membrane, cytoplasm, and organelles for essential functions. Cell adaptations like long nerve cell extensions facilitate specific functions.