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Summary Study/ revision notes – Topic 3: Voice of the Genome (Biology A-Level Edexcel A Salters-Nuffield)

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Biology A-Level

Institución
Bachillerato

This document compiles study notes on Topic 3 (Voice of the Genome) of the Biology A-Level (Edexcel A Salters-Nuffield) course.

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Subido en 26 de enero de 2023
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Tipo Resumen

biology
alevel
biology a level
salters nuffield
biology a
topic 3
biology
a level
salters nuffield
option a
topic 3
voice of the genome
edexcel a

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Estudio Bachillerato
Grado Biology A-Level
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LUCIA ROMERO

TOPIC 3:
VOICE OF THE GENOME

1

,LUCIA ROMERO

3.1. & 3.2. EUKARYOTIC CELLS
Animal cells

Nucleus

→ Nucleus contains a nucleolus and chromatin

Nucleus: controls transcription of DNA, therefore, production of proteins

Nucleolus: makes ribosomes

Nuclear pore: allows passages of substances, e.g., mRNA can leave

Lysosome

→ Membrane bound circular organelle with no clear internal structure

Function:

1. Contains digestive enzymes that break down invading foreign cells, e.g., pathogens
2. Simply worn-out parts of the cell

Ribosome

→ small organelles with no plasma membrane. Can be found freely in the cytoplasm or attached to rough endoplasmic reticulum

Function:

1. Where protein synthesis occurs

Rough Endoplasmic Reticulum (RER)

→ Fluid filled membrane bound sacs. Ribosomes attached to the surface

Function:

Folds + processes new proteins

Smoot Endoplasmic Reticulum (SER)

→ Like rough ER in terms of structure but has no ribosomes

Function:

1. Synthesizes and processes lipids

2

,LUCIA ROMERO

Golgi apparatus

→ Also, fluid filled membrane sacs, often seen with vesicles nearby

Function:

1. Further processes the proteins
2. Packages proteins + newly synthesized lipids
3. Synthesizes lysosomes

Centriole

→ Mostly found in animal cells

Structure:

Made up of hollow tubules called microtubules (tiny protein cylinders)

Function:

Separating chromosomes during cell division

Mitochondrion

Structure:

• Double membrane, inner membrane is folded to form cristae.
• Inside is the matrix
• Where enzymes needed for respiration are found

Function:

1. To produce ATP in respiration
→ releases energy

3.3. ROUGH E.R AND GOLGI APPARATUS
Protein production & transport

Free ribosomes → make proteins that remain within the cell (intracellular proteins)

Ribosomes bound to rER → make proteins that leave the cell / become embedded in the plasma membrane (e.g., digestive enzymes + CFTR
protein)

Process

1) The rough endoplasmic reticulum helps to fold and process the proteins made
on the attached ribosomes.
e.g., a sugar chain may be added to form a glycoprotein
2) The Golgi apparatus further processes the protein
e.g., trimming the sugar chain or adding another sugar chain
It is then packaged into a vesicle ready for transport to the cell membrane or out of the
cell – exocytosis

3

, LUCIA ROMERO

3.4. & 3.5. PROKARYOTIC CELLS
Structure of a prokaryotic cell

Components of a prokaryotic cell

1) Plasma membrane

• Similar to eukaryotic membrane

Made mostly of...

1. Proteins
2. Lipids

2) Cell wall

Made of...

1. Murein (a glycoprotein)

3) Pili

Some prokaryotic cells have them

Function:

1. Transfer genetic material to other cells
2. Help stick cells together

4) Slime capsule

Present in some e.g., bacteria cells

Function:

1. Help defend against attack from immune system

5) Mesosome

It is a folding of the cell membrane inwards

Debated whether...

1. It occurs for cellular processes

Or

2. It is an artefact that happens when the cell is handled to be placed on a microscope slide

6) Ring of DNA (plasmid)

• Separate section of genetic material that → can be transferred from one cell to another

4

, LUCIA ROMERO

7) Coiled strand of circular DNA

→ Free floating in the cytoplasm: not membrane bound

8) Flagellum

Not present in all cells, and others have more than 1

Function:

1. Movement

9) Cytoplasm

→ No membrane bound organelles, do have ribosomes (much smaller than in eukaryotic cells)

Under an electron microscope

3.6. & 3.7. GAMETES AND FERTILISATION
The mitotic index

𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑒𝑙𝑙𝑠 𝑤𝑖𝑡ℎ 𝑣𝑖𝑠𝑖𝑏𝑙𝑒 𝑐ℎ𝑟𝑜𝑚𝑜𝑠𝑜𝑚𝑒𝑠 Because when cells divide,
𝒎𝒊𝒕𝒐𝒕𝒊𝒄 𝒊𝒏𝒅𝒆𝒙 = the chromosomes
𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑒𝑙𝑙𝑠 𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑
condense and become
fatter

Tells you how many cells proportionally are dividing in a sample

How is it useful? – in checking for cancers, because cancer leads to a faster rate of cell division

Structure of gametes

Egg cells

- They are much larger than sperm cells
- They contain huge food reserves to nourish the embryo

5

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