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Global Summary Genetics First Exam
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Genetics Notes – Thijs RoodChapter 9 – Molecular structure of RNA and DNA
Four criteria of genetic material:
1. Information: all the information to construct an organism
2. Transmission: during reproduction from parent to offspring
3. Replication: copy its own content
4. Variation: variance from person to person and able to evolve
Important starter terms:
- Genome = organisms total genetic code/DNA
- Phenome = observable physical or psychological features
- Gene = contains enough DNA for one protein
- Allele = variant of a gene that contribute to phenotype variation can be either
paternal/maternal, recessive/dominant
- Nucleotide = Phosphate + sugar + base, nucleoside = sugar + base
- Chromatid = half of chromosome before duplication held together by centimetre
Scientists and their discoveries:
Griffith: Genetic material from bacteria could transform.
Avery, MacLeod, McCarty:
o Note: Protease and DNase (notice -ase) break down certain molecules
Hershey and Chase: Virus inject genetic information (DNA) into cells (?)
o Note: Proteins contain sulphur and DNA contains phosphorus atoms
Pauling:
Franklin: X-ray diffraction
Chargaff: Amount %A = %T, %G = %C
Watson and Crick: Structure of DNA
DNA and RNA are both nucleic acids. Nucleotides are linked together to form strands. A nucleotide is
composed of phosphates, a sugar and a base. For DNA these are G-C, A-T. The bonds between G-C
are stronger as there are 3 hydrogen bonds. The bases A and G are larger (double ring) and are
purines, the other bases are smaller and are pyrimides.
The nucleotides are covalently attached with phosphodiester linkages. The double helix B DNA has a
right-handed double helix which is antiparallel and has major and minor grooves. The alternative Z
DNA is left-handed. Under certain conditions DNA can form a triple helix structure with specific base-
pairing rules. The polarity is determined by the way in which the nucleotide subunits are linked to
each other.
For RNA the bases are G-C and A-U. An extra Oxygen molecule is attached to the 2’d atom in the D-
Ribose. RNA can form double-stranded helical regions and fold into three-dimensional structures.
, Chapter 12 – Gene Transcription and RNA modification
DNA -> transcription -> RNA -> translation - > POLYPEPTIDE
A gene is a sequence of DNA that encodes for a certain thing. The start of transcription is signalled
by a promoter and the end by a terminator. Regulatory sequences can influence the rate of
transcription. Genes that encode for a specific polypeptide the gene sequence also has a start and
stop codon.
The template/antisense strand is being transcribed into a mRNA from 3’ to 5’ by RNA polymerase.
The formed strand is equal to the coding/sense strand.
Prokaryotes
Bacterial promoters recognise elements at the -35 and -10 sides. During initiation the sigma factor
binds to the major groove and recognises elements at the promoter. A closed complex is formed
after which sigma is released. During elongation that follows the RNA polymerase slides over the
DNA and the open complex looks for complementary base pairs. In bacteria termination can occur
by a rho-dependent or -independent mechanism.
Eukaryotes
RNA polymerase I: all rRNA except 5S rRNA
RNA polymerase II: all mRNA, snRNA, non-coding RNA
RNA polymerase III: all tRNA also a few non-coding RNAs
In eukaryotes a core promoter and also other regulatory elements are found (enhancers and
silencers). Five general transcription factors and a mediator are needed to form an open complex. In
order these are TFIID, TFIIB, RNA polymerase II, TFIIF, TFIIH/TFIIE. They can turn specific genes on or
off.
Modification
RBA transcripts are modified in various ways:
Processing
Splicing: ribozyme or spliceosome
5’ capping: The 5’cap consists of a 7-methylguanosine (eukaryotes)
3’ Poly A tail: The polyA tail consists of Adenine (eukaryotes)
RNA editing: RNA editing changes the base sequence of any after synthesis
Base modification
Group I and II introns are removed by self-splicing, forming mature mRNA. The pre-mRNA introns
are removed via the spliceosome. The spliceosome is a multiunit that can recognise these introns
and remove them. Alternative splicing might occur because of splicing factors (proteins), they
regulate which exons are included in the mature mRNA.
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