1. Nucleic Acids [revise Higher notes]
DNA and RNA are information carrying molecules
DNA: info storage & transmission
RNA: protein synthesis
Based on a SUGAR PHOSPHATE BACKBONE
Base coding A-T and G-C enables a variety and diversity of proteins

2. Nucleotide

3. Nucleotides Monomer of nucleic acid Consists of 3 main parts :
a PENTOSE sugar (deoxyribose/ribose)
a PHOSPHATE group (PO42-)
a nitrogenous base PURINE or a PYRIMIDINE

5. Phosphodiester Bond
Chains of nucleotides (polynucleotides) formed by DEHYDRATION SYNTHESIS reaction between the phosphate group of one nucleotide and the hydroxyl group on the sugar of another nucleotide
This bonding gives polynucleotides a defined polarity reflecting the component nucleotides

6. Phosphodiester bond

7. DNA a double stranded helix
two polynucleotide chains that run in opposite directions (anti-parallel)
one purine pairing with its complementary pyrimidine base
the helix is the only shape that accommodates the purine-pyrimidine base pair and maintains stable hydrogen bonds

8. RNA
3 types of RNA which are SINGLE stranded but can fold to give 3D shapes or conformations:
mRNA – information transcribed from a DNA molecule and transports it to a ribosome
tRNA - collects amino acids and transports them to a ribosome to be fitted according to the messenger RNA code
rRNA (ribosomal RNA) - provides a major structural support component of the ribosome

9. Polymerase enzymes DNA REPLICATION: enables a complete copy of
the genome to be passed on to each daughter
cell during mitosis
TRANSCRIPTION OF DNA into RNA:
mechanism by which genes are expressed
DNA polymerase

10. DNA Ligase
This enzyme forms phosphodiester bonds which are used to join DNA molecules or fragments together to produce recombinant DNA (recDNA)
Polymerases, ligases and restriction endonucleases
(cut DNA) are important components of a genetic
engineer’s ‘toolkit’.
They are used to manipulate DNA

11. Cell Membranes
The cell membrane/plasma membrane represents the barrier that separates the cell’s contents from the surrounding environment and controls what moves in and out
In eukaryotic cells, membranes are also used to generate compartments within the cell, each with a specialised function e.g. golgi apparatus, endoplasmic reticulum, lysosomes etc.

12. Membrane functions Provides selectively permeable barriers
Compartmentalisation
Localises reactions in the cell
Transport of solutes (active transport)
Signal transduction – receptor proteins on the membrane surface recognise and respond to different stimulating molecules, enabling specific responses to be generated
Cell to cell recognition – the external surface of the membrane represents the cell’s biochemical “personality”

13. The Plasma Membrane

14. Types of Membrane Proteins
Proteins approx. 50% of the mass of the plasma membrane and can be classified into different groups depending on their arrangement in the membrane and/or their function
INTRINSIC - proteins may be embedded ce
TRANSMEMBRANE – proteins run through completely
EXTRINSIC – proteins may be on surface
Glycoproteins – proteins may have carbohydrates attached

15. Functions of Membrane Proteins
The main functions of these membrane proteins are as follows: Transport Cell recognition Receptor sites Enzymes Intercellular Junctions

16. TRANSPORT PROTEINS
Transport non-diffusable Channel proteins – provide a ‘pore’ across the membrane through which molecules (usually small and charged) can diffuse Carrier proteins – these are more specific with binding sites for only one solute Both these proteins permit passive transport (with a concentration gradient this is called facilitated diffusion) To transport molecules against the concentration gradient, special types of the carrier proteins are needed. These harness energy to drive the transport process during active transport e.g. sodium-potassium pump

17. CELL RECOGNITION PROTEINS
usually glycoproteins
the carbohydrate chain of the glycoprotein projects out of the cell
the immune system can recognise it’s own cells and organs e.g. ABO blood group antigens:
A = glycoprotein antigen A
O = no glycoprotein antigens

18. RECEPTOR PROTEINS
These have a specific conformation (shape) that allows binding of a particular molecule (the ligand)
The binding of the ligand will then trigger a response in the cell

19. ENZYMES A protein that catalyses a specific reaction
Some receptor proteins have enzymatic activity; the cytoplasmic portion of the protein catalyses a reaction in response to binding a ligand

20. INTERCELLULAR JUNCTIONS
PLASMODESMATA
although each plant cell is encased cell wall, fine strands of cytoplasm, called plasmodesmata, extend through pores in the cell wall connecting the cytoplasm of each cell with that of its neighbours allowing direct exchange of materials

21. In ANIMALS, there are 3 types…
Spot desmosome – dense protein deposits that hold adjacent cells together like rivets. Mechanical strength is provided by the intracellular filaments passing from one desmosome to another
Tight junction – adjacent membrane proteins are bonded together preventing movement of materials in the space between the cells e.g. between epithelial cells lining the small intestine
Gap junction – doughnut shaped proteins from each cell joined together to form tiny channels allowing the passage of small molecules such as ions, amino acids and sugars

22. The Cytoskeleton
The eukaryotic cell is a 3D structure. It has a cytoskeleton anchored to proteins in the plasma membrane
These proteins both maintain shape and allow movement
The cytoskeleton is a dynamic structure, as the microfilaments and microtubules can depolymerise and repolymerise very easily
MICROFILAMENTS
INTERMEDIATE
FILAMENTS
MICROTUBULES

23. The Cytoskeleton 1) Actin filaments/microfilaments
The cytoskeleton is made up of 3 components, in order of increasing diameter. They are …
1) Actin filaments/microfilaments
2) Intermediate filaments
3) Microtubules

24. Microfilaments These are composed of actin (protein)
2 strands of protein molecules twisted together about 7nm in diameter
These are present throughout the cell but are most highly concentrated just inside the plasma membrane
They are important in all cell movement and contraction
Actin fibres in a cell stained with a fluorescent strain specific for actin

25. Intermediate Filaments
tough fibrous protein strands twisted together about 10nm in diameter
very stable structures provide mechanical strength to animal cells which lack the strong cell walls of plants
The nucleus in epithelial cells is held within the cell by a basket like network of intermediate filaments made of keratins which have been stained here using a fluorescent stain

26. Microtubules growing in vitro from an isolated centrosome
hollow tubes (like straws)
tubulin protein (a globular protein)
cylindrical arrangement
a relatively rigid structure
Microtubules only form around a centrosome (organising centre)
The centrosome provides a “place” from which the microtubules form.
important in cell division as part of the spindle fibre network
can move components within the cell
Microtubules growing in vitro from an isolated centrosome

27. Functions Primary importance of the cytoskeleton is in cell motility.
All of these components give mechanical support and shape to the cell
Primary importance of the cytoskeleton is in cell motility.
The cytoskeleton extends throughout the cytoplasm
determines the internal movement of cell organelles,
cell locomotion and muscle fibre contraction

28. Sodium-potassium pump
Cells maintain sodium and potassium against
concentration gradient.
Transmembrane protein and ATP involved.
3 Sodium pumped out and 2 potassium pumped in.
ATP changes shape of protein with phosphate.
(ATPase)
Nerve impulse transmission and ion balance.
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