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Summary BBS1001 The LEGO Bricks of Life
- Instelling
- Maastricht University (UM)
Summary study book Molecular Biology of the Cell of Bruce Alberts, Alexander Johnson - ISBN: 9780815344643, Edition: 6, Year of publication: - (-)
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Voorbeeld 3 van de 24 pagina's
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Course BBS1001: The LEGO Bricks of LifeFats and sugars
Saturated fats:
o Very stable and hard to break up
o No double bonds, maximum amount of H
o Can store more energy
o Likely to stick as cholesterol, therefore considered the “unhealthy” fats
Unsaturated fats:
o One or more double bonds, and thus easier to break up
o Cis and trans double bonds
Sugars
Needed why?
o Fats helps
absorb vitamins,
component of
cell membranes,
long term energy, maintain body temperature,
protect vital organs, part of the myelin
o Sugars quick energy, short time reserve energy storage, structural function
(cellulose almost completely L-glucose), some organs only work on sugar
Digestion of fat
1. Emulsion by bile acids
2. Coats fat droplets bigger surface micells are formed by bile salts
3. Fat is broken down into 1 glycerol and 3 fatty acids by pancreatic lipase
4. Absorption
Passes wall of small intestine and enters the epithelial cell (enterocyte)
Re-synthesized back into triglyceride which is coated by protein
Makes fat-water soluble
Can travel out of the epithelial cell and enters the lymph-vessels and after
that the bloodstream
Digestion of sugar
o Glucose: Krebs cycle and glycolysis ATP production
o Steps
Amylase breaks the sugars in smaller particles (salivary glands)
Stomach acid makes amylase dysfunctional and breaks the sugars further
into smaller pieces monosaccharides
Further broken down in small intestine (lactase breaks down lactose etc.)
Essential fatty acids
o Omega 6 gamma linolenic acid, treat symptoms of heart diseases
, o Omega 3 alpha linolenic acid, formation of cell membranes, circulation and
oxygen uptake
Nomenclature
o Omega where the double bond is, called from not the COOH part (last C is called
Omega)
o Delta where the double bond is, called from the COOH part (first C is called Delta)
o N number of C
o C:N number of C atoms : number of double bonds
Chemical evolution
How can a ribosome be used to create proteins when a ribosome is a protein a well?
o Ribozyme piece of RNA which can behave like an enzyme and therefore can
synthesize itself
Composition of DNA
Phosphate group, sugar group (deoxyribose),
nitrogen base (A, T, G, C)
o Chargaff rule: equal number of purines
(A, G) and pyrimidines (U, C, T)
Double helix structure formed by hydrogen
bonds minor and major groove
Nucleoside = sugar + base
Nucleotide = sugar + base + phosphate
Distance between basepairs: 0.34 nm
Differences RNA and DNA
Uracil instead of Thymine
o Less expensive to produce
o In DNA, Uracil is produced by the chemical degradation of cytosine for RNA is
quantity important but not lifespan
Ribose instead of desoxyribose
Different forms of RNA
Messenger RNA
o Carries the genetic code copied from the DNA during transcription in form of triplets
64 possible codons, 20 represent amino acids, 3 stop codons
o 5’ end is capped with guanosine triphosphate nucleotide, 3’ end has a poly-A-tail
Ribosomal RNA
o Two units in ribosomes which have their own RNA
o Combines with proteins to form ribosomes
o Facilitate the assembly of amino acids to form a polypeptide chain
Transfer RNA
o Transfers amino acids during protein synthesis
o Cloverleaf structure
o Only the nucleotides can be recycled anticodon of the mRNA
Small nuclear RNA
o Forms complexes with proteins which are used to pre-slice RNA
o Recognizes splice sites of the RNA and binds the end of two exons together
Transcription process
Prokaryotes
, 1. Initiation by RNA polymerase holoenzyme (does not require primer) from promotor
sequence
-35 region (sigma factor binds), -10 region (Pridnow box), +1 (transcription
starts)
2. Elongation
3. Termination rho independent (specific sequence and hairpin) or rho dependent
(rho protein)
Eukaryotes
1. Initiation by RNA polymerase and several other proteins
-75 region (CAAT box, sigma factor), -25 region (TATA box), +1 (transcription
starts)
2. Elongation: RNA polymerase is reading from 3’ to 5’ but synthesizing from 5’ to 3’
3. Termination: different for each type of RNA polymerase (I, II, III)
Product is pre-mRNA still needs post transcriptional modifications
Replication process
1. Topo-isomerase type 1 unwinds the DNA (removes supercoiling)
2. Helicase breaks interactions between base pairs
3. Primer (=short piece of RNA) binds to 3’ end
of the leading strand
4. DNA polymerase type II is responsible for
the elongation
5. DNA polymerase type I removes all primers
which are replaced by appropriate bases
6. DNA polymerase type III checks the newly
formed bases
7. DNA ligase joins the Okazaki fragments
8. Topo-isomerase type 2 creates supercoiling
Differences DNA polymerases and RNA polymerases
DNA polymerases RNA polymerases
Replication Transcription
Needs primer Doesn’t need primer
Fast 10% slower
Proofreading mechanism No proofreading mechanism
Attack 3OH group Doesn’t need the 3OH group
Reads from 3’ to 5’ and synthesizes from 5’ to 3’
Post transcriptional modifications
Splicing introns are removed from the RNA by U1, U2, U3, U4, U5 and U6
5’ capping the triphosphate group is replaced by the “cap” = guanine triphosphate
o Prevents from enzymatic degradation, assists in export to cytoplasm, increases
stability, serves recognition point for ribosome
Poly-A-tail string of adenine bases attached to the synthesized end of RNA, catalyzed by
poly (A) polymerase
o Protects RNA from enzymatic degradation, helps in translation
Prokaryote is polycistronic (transcription and translation at the same time), eukaryote is
monocistronic (first transcription, then translation)
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