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The nucleus and genome organisation (DNA (Consists of a double helical…
The nucleus and genome organisation
What is a genome
A genome can be defined as an organism's complete set of DNA , including all of its genes.Each genome contains all the information needed to build and maintain that organism
Sequence classes in the human genome
1% protein- coding genes , 4% RNA gene regulatory sequences, 44% other sequences, 45% transposon based repeats, 6% heterochromatin
Protein - coding genes examples:
Dystrophin = Protein, largest in size, takes 16 hours to transcribe
SRY = smallest size, determines sex
Human Genome = 2 parts
Nuclear genome 26'000 genes
Mitochondrial genome = 37 genes
Bears similarities to the compact genome of prokaryotes
A copy of entire genome, is contained in all cells that have a nucleus
Central dogma of molecular biology
DNA -- Transcription --> RNA -- Translation --> Proteins
The information coded in the DNA directs the synthesis of proteins
DNA
Consists of a double helical sugar - phosphate structure with the two strands held together by hydrogen bonding between adenine and thymine or cytosine and gaunine bases
The sugar is deoxyribose - ribose missing an oxygen atom at its 2' position
Each DNA strand consists of alternating deoxyribose molecules connected by phodphodiester bonds from the 5' position of one deoxyribose to the 3' position of the next
G-C = Three hydrogen bonds
A-T = Two hydrogen bonds
C value paradox
The amount of DNA in a haploid gene does not seem to correspond strongly to the complexity of an organism
G value complex
There is no correlation between the number of genes and complexity
Gene: The basic physical and functional unity of heredity: A gene controls the transmission and expression of one of more traits
20,000 protein-coding genes plus 6,000 RNA genes (provisional) total 26'000 genes
Genes in simple organisms - such as bacteria are comparatively similar in size and usually short.
In complex Eukaryotes genes show huge variation in size
Eukaryotes = Organisms whose cells contain nuclei and other organelles enclosed membranes
The nucleus:
House DNA and directs the synthesis of ribosomes and proteins
Enclosed within an envelope consisting of two parallel membranes separated by an inter membrane space
Compartmentalised
Tends to be the most prominent organelle
Prokaryotes = single celled organisms lacking a membrane - bound nucleus
Can acquire compounds from their local environment or synthesise them by enzymatic pathways
Regulatory mechanisms: recognise environmental conditions in which they should activate or repress the transcription of the relevant genes
Nuclear envelope:
Composed of two membranes separated by an intermembrane space
Inner membrane lined by the nuclear lamina, a meshwork of lamin proteins + allow rigidity and anchorage
Nuclear pores allow a two - way traffic of proteins and nucleic acids between the nucleus and the cytoplasm (2000-4000 per membrane)
Transport to and from the nucleus is mediated by the nuclear pores - Regulate the movement of macromolecules
RNA and ribosomal sub units have to enter the cystoplasm, and proteins must enter the nucleus
Pores are made from a large number of proteins
Transport is complex and requires both energy and transporter proteins
2000-4000 nuclear pores per membrane
Nuclear pore complex
Nucleoplasmic face: The ring of the NPC supports 8 filaments
Cytoplasmic face: supports 8 cytoplasmic filaments
Centre of the NPC: central plus or transporter proteins and spoke which connects the two rings together
Nuclear export: 560'000 proteins
Nuclear Import: 14'000 proteins
GTPase: Enzyme that can bind and hydrolyse GTP: It provides energy for transport
Nuclear compartments:
Nucleoli: where ribosomes are made
Mostly chromatin (heterochromatin and euchromatin)
Heterochromatin: more condensed, cannot be transcribed. Associated with tight histone binding
Euchromatin: less condensed, can be transcribed. Euchromaitin is marked by relatively weak binding.
Nucleosome:
Basic level of DNA packaging
147 bp of DNA wrapped around a complex of eight core histone molecules
Genes are unevenly distributed along the genome