CF

Biology Part II

Part 02

The Cell Cycle

Is the life cycle of a cell, and its different stages

  • Cells go through this cycle to grow and divide to make new cells

  1. Interphase

  • G1 (Gap 1)

—> The cell grows and does its normal job

—> Where the cell spends most of its time

  • S (Synthesis)

—> The cell copies its DNA so when it divides, each new cell gets a full set

  • G2 (Gap 2)

—> The cell checks the copied DNA for mistakes and prepares to divide

  1. Mitosis (PMAT)

—> When the cell actually divides its nucleus

  1. Cytokinesis

—> The rest of the cell (cytoplasm) splits, making two separate cells

Mitosis - PMAT Breakdown

Mitosis has four main phases

  1. Prophase

—> DNA condenses from loose form (chromatin) into chromosomes (X-shaped structures)

—> The nuclear membrane breaks down

—> Spindle fibers (tiny ropes) start to form

  1. Metaphase (Middle)

—> Chromosomes line up in the middle of the cell

—> Spindle fibers attach to them

  1. Anaphase (Apart)

—> The two halves of the chromosomes (sister chromatids) are pulled apart to opposite sides of the cell

  1. Telophase (Two Nuclei)

—> Two nuclear membranes start to form around the DNA

—> The cell begins to pinch in the middle

Cytokinesis

—> The cytoplasm splits, fully dividing the cell, into two identical daughter cells

—> In animal cells, the membrane pinches inward

—> In plant cells, a new cell wall forms between two new cells

Regulation of the Cell Cycle

The cell cycle is controlled by genes and checkpoints to make sure everything is working properly

  • Checkpoints

—> At different stages, the cell checks if it is ready to move forward. If something is wrong (like damaged DNA), the cell will either fix it or self destruct (apoptosis)

—> Genes like p53 help regulate the cycle. If they get mutated, cells may grow uncontrollably, which can lead to cancer

Chromatin, Chromosomes, and Chromatids

Chromatin

—> Loose, stringy DNA (like spaghetti)

Chromosome

—> Tightly coiled DNA, shaped like an X, visible during cell division

Chromatid

—> One half of a duplicated chromosome. Sister chromatids are identical copies that seperate in anaphase

Karyotypes - Male versus Female

A picture of all the chromosomes in a cell

  • Humans have 46 chromosomes (23 pairs)

  • The last pair are the sex chromosomes

—> XX = Female

—> XY = Male

DNA Structure and Function - The Blueprint of Life

DNA (deoxyribonucleic acid) is like a cookbook that has all the instructions to build and run your body

  • Each cell has a fully copy of this cookbook

Components of a Nucleotide - The Lego Blocks of DNA

DNA is made of small building blocks called nucleotides. Each nucleotide has three parts :

  1. Sugar (Deoxyribose)

  • The backbone that holds things together

  1. Phosphate Group

  • Connects the sugars like a chain

  1. Nitrogenous Base

  • The most important part. It carries the genetic information

Types of Nitrogenous Bases and Base Pairing - Who Matches with Who?

There are four types of bases, and they are super picky about their partners

—> Adenine (A) pairs with Thymine (T)

—> Cytosine (C) pairs with Guanine (G)

Way to Remember

—> A and T = Always Together

—> C and G = Cool Guys

Overall Structure of DNA - The Twisty Ladder

—> DNA looks like a twisted ladder (double helix)

—> The sugar and phosphate make the sides of the ladder

—> The bases (A, T, C, G) make the steps (held together by weak hydrogen bonds)

—> Because of base pairing, one strand always matches the other (complementary)

Telomeres - The Aglets of Shoelaces

—> Telomeres are caps at the end of DNA strands that protect important genetic information

  • Think of them like the plastic tips on shoelaces— without them, the shoelaces (DNA) would fray and get damaged over time

—> Telomeres get shorter as we age, which is why cells stop working properly as we get older

DNA Replication - Definitions

  1. DNA

  • The molecule that carries genetic instructions

  • Looks like a twisted ladder made of nucleotides

  1. Nucleotide

  • The building blocks of DNA

  • Each nucleotide has three parts

—> A sugar, a phosphate, and a base (A, T, C, or G)

—> These bases pair up (A-T, C-G) to form the DNA ladder

  1. Helicase

  • The enzyme that unzips the DNA by breaking the bonds between the bases

  • Separates the two strands so they can be copied

  1. Leading Strand

  • The strand that is copied continuously in one smooth motion

  • DNA polymerase moves in the same direction

  1. Lagging Strand

  • The strand that is copied in small chunks (Okazaki Fragments)

  • DNA polymerase moves in the opposite direction

  1. DNA Polymerase

  • The enzyme that builds new DNA strands by adding nucleotides to match the original strand

  • Works smoothly on the Leading Strand

  • Works in sections on the Lagging Strand

  1. Exonuclease (DNA Polymerase I)

  • A special type of DNA polymerase that removes errors and replaces them

  1. Ligase

  • The enzyme that glues together the Okazaki Fragments on the lagging strand, making it a smooth, continuous piece

  1. Semi-Conservative

  • The final result of DNA Replication

  • Each new DNA molecule has one old strand and one new strand, meaning half (semi) of the original DNA is saved (conserved)