Eukaryotic gene structure Flashcards
What is the diploid nucleus number and the haploid C-value number in human cells?
Diploid = 7pg Haploid = 3.5pg
What is the genome size of human cells?
3.3gb
How can we measure human genome size? (2)
Feulgen staining
DAPI fluorescence vs biochemical standard
What is the genome size also known as?
The C value
What is the definition of the C value?
The C value is the weight in grams of the DNA in a haploid genome
What is the average molecular weight of a base pair?
660Da (Daltons)
What are the calculation steps for working out the C value? (2)
- Genome BP number x average molecular weight (660) = molecular weight (1 mole)
- Weight = molecular weight/avogradros number (6.3x10^23)
Why do multicellular eukaryotes have genomes that encode genes inefficiently? (2)
Introns interrupt genes
Non-gene DNA
What is the explanation for the C value paradox?
Non-coding DNA can be present in variable amounts
They are not directly related to genetic complexity
What do the repetitive parts of a genome contain? (2)
Dispersed repeats
Tandem repeats
What does the non-repetitive part of the genome include?
Unique sequence (intergenic) Introns and exons (genic)
What is the makeup of the human genome in terms of repetitive and Non-repetitive? (2)
Genic - 25% (introns 23%, coding 2%)
Intergenic - 75% (20% unique, 55% repetitive)
What are the general features of gene organisation in eukaryotes? (5)
Telomere Non-coding intergenic sequences Gene (promoter, coding region) Centromere Telomere
What are introns and exons?
Introns: interruptions in coding DNA (non-coding DNA)
Exons: coding DNA
When are introns removed?
Post-transcriptionally
What happens when splicing occurs? (2)
In the nucleus, pre mRNA
Processing - splicing occurs, exons joined together and introns removed by spliceosomes
What are the advantages to retaining intron/exon organisation of genes?
Some genes have optimal exons
Allows for alternative splicing (not just one after another)
More than one protein form per gene
How are the beginnings and ends of introns recognised so precisely?
Promoter region
How do tandem repeats occur?
Arise from replication slippage
Why are inverted repeats unstable?
Unstable due to forming a hairpin structures that are attacked by nucleases
