What is a zygote?
A fertiliser egg -> Replicates itself during mitosis
Why do cells replicate?
- Growth & development
- Maintenance & repair
How does cell replication assist in growth & development?
- New cells grow in size, which increase size of organism
- Individuals develop -> Cells become specialised
- More replications -> Specialised cells become organised into tissues -> Form organism’s body
How does cell replication assist in maintenance & repair?
- Maintaining and repairing damaged tissues requires production of identical new cells to replace dead cells
- New cells produced by mitosis
What is DNA?
Nucleic acid responsible for storing genetic info in cells
Contains info for growth, survival & replication
What is the structure of DNA?
- 2 chains twist around to form double helix structure
- Building blocks called nucleotides
- Guanine-Cytosine, Adenine-THYMINE
What is RNA?
Type of nucleic acid responsible for interpreting genetic info into proteins
What is the structure of RNA?
- Nucleotides -> Contain sugar, phosphate and nitrogenous group
- Specific type of nucleotide called ribonucleotide
- Guanine-Cytosine, Adenine-URACIL
What are the 3 steps of DNA replication?
- Unravelling the DNA
- Building a new DNA strand
- Forming the DNA backbone
What occurs during unravelling the DNA?
Enzyme helicase breaks hydrogen bonds between bases, ‘unzipping’ the double helix into two single strands
What occurs during building the new DNA strand?
DNA polymerase helps bind free nucleotide in cell nucleus to the single strand
What does semi-conservative mean?
When DNA is produced, one of the strands in each new DNA molecule comes from old DNA molecule
What occurs during forming the DNA backbone?
- DNA polymerase stitches newly joined nucleotides together -> Sugar-phosphate backbone is formed
- Enzymes catalysts condensation reaction between adjacent phosphate + sugar
- Two identical DNA strands are formed, wound into double helix
What is a leading strand of DNA?
Moves in 5’ to 3’ direction towards fork. Adds bases continuously one by one
What is a lagging strand of DNA
Moves in 3’ to 5’ direction. Sections of DNA are added in okazaki fragments
What is cell replication?
Process -> Cells replicate genetic material and divide to form new cells
What is mitosis?
Type of cell division where 1 parent cell divides once to produce 2 identical daughter cells
What are the stages of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
What happens during the Prophase of mitosis?
Chromatin shortens and thickens to form chromosomes
What happens during the Metaphase of mitosis?
Chromosomes line up individuality along the MIDDLE of cell -> Spindle fibres attach to centromeres
What happens during the Anaphase of mitosis?
Spindle fibres shorten, centromeres break and chromatids move apart. Chromosomes pulled towards OPPOSITE poles of cell
What happens during the Telophase of mitosis?
Cytoplasm separates (cytokinesis), cell and nuclear membranes form, chromosomes uncoil -> 2 identical daughter cells form
What is meiosis?
1 parent cell divides TWICE to produce 4 NON-IDENTICAL daughter cells
What happens in Meiosis I?
- Interphase I: DNA replicates
- Prophase I: Chromatin shortens + thickens to form chromosomes
- Metaphase I: Chromosomes line up in homologous pairs
- Anaphase I: Crossing over occurs
- Telophase I: Spindle fibres attach, shorten and homologous chromosomes break apart
- Cytokinesis: Cells completely divide, only one of each homologous chromosome on each cell
