lecture 2 - normal genome Flashcards
(34 cards)
how many base pairs is the human genome comprised of?
3.2 billion base pairs of DNA.
what are nucleotides comprised of
phosphate
base
sugar - ribose or dexoyribose
How is DNA packaged in the nucleus?
DNA is coiled into helix = wound around histones = nucleosomes = packaged into chromatin fibers, = loops,= chromosomes.
packaging of human nuclear genome
- dna double helix
- chromatin
- chromatin fibre packed into nucleosomes
- extended chromosome
- condensed chromosomes
- entire mitotic chromosome
what is a karyotype
the complete set of chromosomes of an organism showing:
chromosome number - 46 for humans
size and shape
banding pattern
what can karyotypes be used to show
diagnosis - e.g. trisomy 21 = down syndrome
detecting structural rearragements - e/g/ deletions. translocations
sex determination
comparitive genomics across species
what are chromosomes with very short p arms called
acrocentric chromosomes
How many pairs of chromosomes do humans have?
Humans have 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes (XX for females, XY for males).
What are histones, and how do they regulate chromatin structure?
Histones are proteins around which DNA is wound. They can be post-translationally modified to regulate chromatin structure.
what is a gene?
a gene is a unit of DNA that encodes an RNA or protein product
how many DNA/RNA polyermase
1 DNA
3RNA
What enzyme transcribes protein-coding genes?
RNA polymerase II
In which direction is the nucleotide chain synthesised during RNA transcription?
5’ → 3’ direction.
Are genes equally distributed across all chromosomes?
No. Some chromosomes are more gene-dense than others.
what are small and large genes called
small - OMG
large - NF1
What is the approximate number of protein-coding genes/promoters/enhancers in the human genome?
around 20,338 protein-coding genes.
70,292 promoters
399,124 enhancers
what are the first 4 steps of pre-mRNA splicing
- exons 1 and 2 with an intron line between them - intron needs to be cut out leaving only exons left
- at the 5’ end, splice donor site, theres a short sequence - where the spliceosome makes its first cut
- branch point “A” - downstream of donor - between A and splice acceptor is the Cs and Ts - polypyrimidine tract - helps splicesome line everything up
- at 3’ emd, the splicesome makes second cut
what are the last 3 steps of pre-mRNA splicing
- first transesterifcation the 2’-OH of the branch point attacks the 5’ splice doner - cutting between exon 1and intron and linking the intron’s 5’ end to the “A” = looped lariat
- second transesterification - newly freed 3’-OH of exon 1 attacks 3’ splice acceptor, cutting before exon 1 and 2 join
- intron release and degradation- lariat is released from splicesome, then debranched and degrades = spliced mRNA
What percentage of the genome undergoes alternative splicing?
Around 95% of multiexon genes undergo alternative splicing.
What are the three stages of translation?
Initiation, Elongation, and Termination.
what is the components of a cloverleaf tRNA
- bottom loop = anticodon loop - triplet of bases that base pairs with the complementary mRNA codon
- top 3’ end : single stranded CCA sequence where the corresponding amino acid is enzymatically attached
- left and right loop - structural loops contained modified bases that help tRNA fold correctly and interact with the ribosome and enzyme
- acceptor stem - vertical stem - paired region that included the CCA tail, forming the handle for amino accid attachement
What is the function of the A site in the ribosome?
The A site binds to tRNA carrying an amino acid during translation.
True or False: Genes are only found on the forward strand of DNA.
False. Genes can be found on both strands of DNA.
True or False: Genes can overlap on chromosomes.
True. Genes can be arranged in the same or opposite directions on a chromosome.