Cell Replication

• Telophase

  Daughter chromosomes gather at opposite poles and nuclear membranes form nuclei around them, plant cell only - cell plate forms to become new cell wall, cell elongates and continues to cleave, cytokinesis (division of cytoplasm) occurs
• Metaphase

  Chromosomes are lined up on metaphase plate ('equator'), centrioles build spindle fibres, centromeres join to spindle fibres
• Prophase


  1. Early: Chromosomes fully condensed, two vertical arms of chromosomes called sister chromatids connected by centromere, centrioles duplicate

  2. Mid: Centrioles move in opposite directions, nuclear membrane breaks down, chromosomes start to line up on metaphase plate

  3. Late: Centrioles arrive at opposite ends of the cell, nuclear membrane has completely broken down
• Meiosis

  Cell division that results in 4 daughter cells, half the number of chromosomes of the parent cell (1n), produces genetically different daughters, genetic variations, reductive division from 1 diploid (2n) divides into 4 haploid (1n)
• Interphase

  1. G1 (growth phase)

  2. New cell grows and replicates organelles in the cytoplasm

  3. Chromosome number is diploid (2n)

  4. Chromatids have not replicated yet

  5. S phase (synthesis phase)

  6. DNA in the nucleus replicates itself

  7. There is double the genetic material (2 chromatids) joined at the centromere = still diploid (2n)

  8. G2 (proofreading)

  9. The cell continues to grow and gets ready for the next cell division (mitosis and cytokinesis)
• Cell cycle

  1. Division + enlargement of cells occur

  2. Interphase (completed in 18-22 hours)

  3. Mitosis (completed in 1-2 hours)
• Mitosis


  Form of cell division that results in 2 identical daughter cells
• Mitosis

  1. 4 main stages: PMAT + C

  2. Prophase

  3. Metaphase

  4. Anaphase

  5. Telophase

  6. Cytokinesis
• Anaphase


  Chromosomes pulled apart, sister chromatids move to opposite ends of the cell along the spindle fibres, centriole assists spindle fibres in pulling the daughter chromatids towards the poles, cell starts to elongate and cleave
• Meiosis I


  Prophase I: Chromosomes separate into homologous pairs that start to move to metaphase plate, nuclear membrane breaks down, centrioles duplicate + move towards poles, crossing over occurs
• Metaphase I


  Chromosomes align in pairs along the metaphase plate
• DNA structure

  • Double helix structure
  • Long strands of DNA are wound up and packed in the nucleus
  • In the form of chromosomes
• Process of DNA replication

  1. Double helix unwinds

  2. Topoisomerase relaxes DNA ahead of the replication fork

  3. Helicase unwinds and unzips the double helix by breaking hydrogen bonds between bases

  4. DNA strands separate

  5. Single-stranded binding proteins (SSBs) bind and stabilize the newly separated single-stranded DNA

  6. Nucleotides are added against each single strand

  7. Each strand of the DNA molecule acts as a template for the production of a new strand of DNA

  8. A short strand of RNA (RNA primer) is made and attaches to the DNA

  9. DNA polymerase III adds nucleotides

  10. Continues the synt
• Each daughter cell needs a complete copy of genes
• Mitosis


  1. Metaphase plate

  2. Nuclear membrane breaks down

  3. Centrioles duplicate + move towards poles

  4. Crossing over occurs
• Crossing over

  1. Homologous pairs join together in a process called synapsis

  2. The arms of a pair of homologous chromosomes wrap around each other at the point called chiasmata

  3. Genetic material can be exchanged between paternal and maternal genes

  4. This causes genetic variation
• Cytokinesis

  Cell divides producing 2 genetically different diploid daughter cells
• Nucleotides pair based off the nitrogenous base they carry
• DNA

  Deoxyribonucleic acid
• Telophase I

  1. Spindles disappear

  2. Nuclear membrane forms

  3. Cell elongates and cleaves
• Anaphase I


  1. Sister chromatids remain attached at the centromere

  2. Spindle fibres pull chromosomes to opposite poles
• Nitrogenous bases

  • Adenine + thymine
  • Guanine + cytosine
• Nucleotide

  A strand of DNA made of sugar (deoxyribose) + phosphate + nitrogenous base
• DNA replication occurs during interphase
• Meiosis II

  1. Prophase II

  2. Metaphase II

  3. Anaphase II

  4. Telophase II

  5. Cytokinesis
• Enzymes involved in DNA replication

  1. Topoisomerase

  2. Helicase

  3. DNA polymerase ll

  4. DNA polymerase l

  5. Primase

  6. Ligase
• Nucleotides are strongly held together to form the DNA double helix shape by the hydrogen bonds formed between nitrogenous bases
• Anti-parallel strands

  2 strands in a double-stranded DNA molecule run in opposite directions
• DNA replication produces an exact copy of genetic information prior to cell division, daughter cells will have all genes and chromosomes, repair enzymes correct errors as DNA replication occurs, mutations may occur if not corrected by repair enzymes
• 3’ and 5’ ends of DNA strands


  Each DNA strand has a 3 prime end (3’) and a 5 prime end (5’), nucleotides are always added to the 3’ end of the DNA strand
• Assess the effect of the cell replication process on the continuity of a species
• Meiosis: All daughter cells contain a copy of all chromosomes/genes, DNA in the original cell is an exact copy of that of the parent, variation introduced through crossing over, random segregation, & independent assortment, mutations (e.g., nondisjunction)
• Meiosis

  Processes involved: Prophase 1 (Crossing over, Nuclear membrane breakdown, Homologous pairs, Centrioles), Metaphase 1 (Line up in pairs, Spindle fibres attach at centromere), Anaphase 1 (Split, Pull away), Telophase 1 (Spindles disappear, Nuclear membrane reforms), Cytokinesis (2 different diploids, REPEATS WITHOUT CROSSING OVER + PRODUCES 4 GENETICALLY DIFFERENT HAPLOID CELLS)
• How is variation introduced?
• Mitosis


  Processes involved: Prophase, Pairing, Nuclear membrane breakdown, Centrioles movement, Metaphase, Anaphase, Telophase
• DNA replication

  1. Each strand of the DNA molecule acts as a template for the production of a new strand of DNA

  2. Short strands of RNA (RNA primer) is made and attaches to the DNA

  3. DNA polymerase III adds nucleotides

  4. Continues the synthesis of a new strand

  5. Nucleotides are always added to the 3’ of DNA strand

  6. Leading strand: Nucleotides are added in a long chain growing in the same direction as the replication fork opens up, replication is continuous

  7. Lagging strand: Nucleotides added in chunks (Okazaki fragments) from the replication fork backward, fragments are joined by ligase to form one continuous strand, replication is discontinuous

  8. Replication errors are identified and corrected by DNA polymerase l 'proofreading’ and ‘editing’, ligase seals 2 new strands together
• How is stability maintained?
• Mitosis creates identical daughter cells, mutations may occur from DNA replication or incorrect assortment of chromosomes into daughter cells