This document offers a selection of summary notes on the chapter: Voice of the Genome. This is based on textbook A-Level Biology A (2015) Salters-Nuffield
, A Level Notes GEN: Protein Transport/Fertilisation/Stem Cells Biology
Protein Synthesis + Transport
1) Transcription of DNA to mRNA inside nucleus
2) Travels to ribosomes on rER where mRNA is translated into protein
3) Proteins enter and move through rER assuming 3D shape en route
4) Vesicles pinch off rER containing protein
5) Vesicles fuse to form flattened sacs of the Golgi Apparatus
6) Proteins are modified here (e.g. sugars added)
7) Vesicles pinch off, travel and fuse with cell surface membrane
8) Release protein (such as extracellular enzymes) via exocytosis
Stages of Fertilisation
1) Receptors on sperm membrane make contact with the zona pellucida
2) Hormones released by ovum cause acrosome to swell
3) Vesicles with digestive enzyme in acrosome fuse with sperm cell surface membrane
4) Exocytosis of enzymes occurs
5) Digestive enzymes from acrosome break down follicle cells and zona pellucida
6) Sperm fuses with ovum membrane; this allows sperm nucleus to enter ovum and fuse with
egg nucleus
ACROSOME REACTION CORTICAL REACTION
→ Acrosome in head of sperm swells, fuses with cell surface → Ovum receptor detects sperm, then releases chemicals
membrane, releases digestive enzymes → Zona pellucida thickens
→ Breaks down zona pellucida → Polyspermy prevented
SIMILARITIES DIFFERENCES
✓ Both involve the release of substance (acrosome in sperm, Zona pellucida broken down in AR, but thickens in CR
chemicals in ovum) AR allows entry of sperm nucleus, CR prevents entry of sperm
✓ Both have specialised lysosomes (acrosome in sperm, cortical
granules in ovum)
✓ Both triggered by stimulus
Totipotent All 216 cell types Embryonic stem cells (early zygote)
Pluripotent Most, but not all Adult stem cells; bone marrow; hair; muscle; in blastocyst
Multipotent/ Unipotent Only some cell types Neural cells; cord blood; cardiac cells; bone marrow
Digestive tissue, nervous tissue, cardiac tissue
Unspecialised cells have no limit to number of divisions → Hayflick Limit
Embryonic Stem Cells Adult Stem Cells
✓ Totipotent; differentiate into any cell type ✓ No rejection; genetically identical
✓ Treat a variety of diseases ✓ No immunosuppressants required
✓ Repair any damages tissue ✓ Less risk of infection
✓ Easier to obtain
Expensive Multipotent; only some diseases cured
Chance of rejection Religious issues (imitating God, etc.)
Destruction of (embryo) potential life
Regulatory body; cost, source, age of embryo, illegal cloning
Implications if discarded IVF embryos used
Plant Reproduction:
How stem cells become specialised: The sperm cells of a flowering plant are contained in
pollen grains. Pollination occurs when pollen grains are
1) Chemical stimulus (e.g. hormone) transported from anthers to stigmas. After the pollen
2) Activates some genes lands on the stigma, a tube grows from the pollen grain
3) Allows transcription of DNA → mRNA through the style of the ovary. Inside the ovary are
4) Translated into protein at ribosomes ovules. Each ovule contain an egg. Sperm cells within
5) Causes structural change of cell the pollen grain move down the pollen tube and into the
6) Cell because differentiated and specialised for a particular function ovule. Fertilization occurs as one of the sperm cells fuse
with the egg inside the ovule.
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