Four stages of the cell cycle
G₁ (Growth 1) Cell grows, carries out normal functions, prepares to copy DNA.
S (Synthesis) DNA is replicated (each chromosome is copied).
G₂ (Growth 2) Final checks and prep for cell division(miitosis).
M (Mitosis) The cell/nucleus divides into two identical daughter cells.
What are the steps of DNA replication
DNA makes an exact copy of itself in the S phase.
Unwinding the DNA:
Helicase breaks hydrogen bonds, separating strands and forming a replication fork.
Each strand acts as a template for a new strand.
Complementary Base Pairing:
Free nucleotides pair with template bases: A–T, C–G.
Building the New Strand:
DNA polymerase adds nucleotides 5’ → 3’.
Leading strand: synthesized continuously.
Lagging strand: synthesized in Okazaki fragments in the opposite direction.
Sealing the Gaps:
DNA ligase joins Okazaki fragments to make a continuous strand.
Result: 2 identical DNA molecules
Define mitosis
Mitosis is the type of cell division that makes two genetically identical body cells (somatic cells).
Purpose of mitosis
To allow for growth, repair, and replacement of cells, and to maintain the same DNA in each new cell.
Factors affecting life processes
Temperature Affects enzyme activity (too high = denatured, too low = slow).
Nutrients Needed for energy and growth (e.g. glucose, oxygen).
pH levels Enzymes work best at specific pH.
Water availability Required for reactions and transport.
Waste build-up Can slow or stop processes if not removed.
Why different types of cells differ in structure to fit their purpose
Example
Leaf cell (palisade cell) Packed with chloroplasts near the surface Maximises light absorption for photosynthesis
Chloroplast Contains thylakoid stacks with chlorophyll Increases surface area to capture light energy
what is theDNA structure
A double helix made of nucleotides (sugar, phosphate, base).
What is the base pairing rulse
A pairs with T, C pairs with G.
what is DNA replication
The process of making an identical copy of DNA (each chromosome) before cell division.
what is Semiconservative in terms of Dna and replication
Each new DNA molecule has one old strand and one new strand.
what areOkazaki fragments:
Short DNA pieces made on the lagging strand during replication.
Enzymes (names) in replication:
Helicase: Unzips the DNA.
DNA polymerase: Adds new nucleotides to growing strand.
Primase:Synthesizes RNA primers to guide DNA polymerase.
Ligase: Joins Okazaki fragments.
What are the leading and laggin strands
Leading strand: Built continuously toward the replication fork.
Lagging strand: Built in fragments away from the fork.
What is the cell cycle
The stages a cell goes through to grow and divide.
What is cytosis
Division of the cytoplasm after mitosis.
mistosis process
Prophase: Chromosomes condense, spindle forms.
Metaphase: Chromosomes line up in the middle.
Anaphase: Chromatids pulled apart.
Telophase: Two nuclei form.
Limiting factors of mitosis (SALE)
Stage of life: Cells divide more during growth or healing.
Availability of nutrients: Needed to build cell structures.
Location of cells: Skin/gut cells divide often; nerve cells rarely.
Environmental factors: Temperature, toxins, or radiation can affect division.
what is a Protein structure:
Made of amino acids folded into a specific shape.
What are copies produced by replication called
The identical copies produced by replication are called chromatids.
When does Dna replication occur
Just before mitosis or meiosis
how are mistakes avoided in replication
The base pairing rule means that only certain bases will pair up.
The bonding between the different pairs is different ie different number of hydrogen bonds A-T (2) G-C (3)
Errors that escape proofreading can result in mutations, which may affect protein synthesis.
DNA polymerase ‘proofreads’ the strand for any mistakes and fixes them.
What are the two types of cell divison and what are they for
Mitosis – cell division for growth and repair.
Meiosis – cell division to produce gametes
(eggs and sperm).
Where does DNA replication occur
Nucleas
When does DNA replication occur in the cell cycle
S phase
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Cell purpose19
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Organelles10
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Enzymes11
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Transport20
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Photosynthesis30
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Respiration21
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Cell Cycle28
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Protein Synthesis9
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Mitosis7
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DNA12
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Meiosis17
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Monohybrid inheritance6
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Dihybrid inheritance4
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Pedigree charts4
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Mutations14
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Genetic Variation4
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Natural selection9
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Definitions77
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Evolution and gene pool9
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Variation12
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Factor’s Causing Change in the Gene Pool19
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Speciation8
