Structure and function of the human genome Flashcards
Describe the structure of DNA
DNA double helix (2 anti-parallel strands) binds to histones
Octamer of histones form nucleosome
What’s the basic structure of nucleotides?
- Nitrogenous base
- Deoxyribose
- Phosphate
What are histones?
Positively charged proteins, attracted to negative charge of DNA, they give DNA support to wrap around
What are the purines?
Adenine and guanine - Contain 2 nitrogenous rings
What are the pyrimidines?
Thymine, uracil and cytosine - Contain 1 nitrogenous base
What’s the relationship between pyrimidines and purines?
Purines bind to pyrimidines (A to T/U, G to C)
Describe the basic structure of chromosomes
- Chromosomes usually exist as chromatin
- DNA double helix binds to histones
- Octamer of histones form nucleosome
- Euchromatin
- Extended state, dispersed through nucleus
- Allows gene expression
- Heterochromatin
- Highly condensed, genes not expressed
- Tips of chromosome = Telomere
- P arm = Short arm
- Centromere
- Q arm = Long arm
What are the 4 types of chromosomes?
- Metacentric - Centromere in middle
- Sub-metacentric - Centromere slightly above middle
- Acrocentric - Centromere far above middle, contain little satellite arms
- Telocentric - Centromere at telomere
How are we able to distinguish between the different types of chromosomes?
- Size
- Banding pattern
- Centromere position
What are the main functions of centromeres?
- Keep sister chromatids together
- Attach to microtubules during cell division
- Rich in heterochromatin
- Normally highly repetitive
What are the main functions of telomeres?
- Protects ends of chromosome
- Telomerase repairs telomeres, only active in certain cell types
- If telomerase switched on in wrong cells, leads to cancer
What are exons?
Parts of the gene that code for and are actually in proteins, not all exons are coding though (Untranslated regions)
Code for amino acids except for untranslated regions (UTR)
What are introns?
Non-coding regions of gene, these are spliced off in pre-mRNA processing
Non-coding section of gene b/w exons
Define genome
Complete set of DNA (genetic material) in an organism
Packages = Chromatin and chromosomes
Describe the nuclear genome
- 22 pairs of autosomes
- 1 pair of sex chromosomes
- Actual DNA sequence
- Transcribed units = genes
- Protein coding
- RNA-only coding, make RNA but not protein
Describe the mitochondrial genome
- D-loop - Contains promoters for light and heavy strands
- 13 coding genes (code for OXPHOS proteins)
- 24 non-coding genes (coding for RNA molecules)
- Only ova provide mitochondria so this is maternal inheritance
Define exome
Parts of genome which code for protein i.e. all coding exons of all genes in the genome
What is the promoter region?
5’ of gene, contains important regulatory elements for transcription
What is the importance of UTR?
Contain regulatory elements, helps to control protein synthesis
Define epigenome
Chemical compounds that attach to DNA or histones and can affect gene activity (e.g. DNA methylation, histone acetylation)
Can:
- Alter chromatin strructure
- Recruit histone modifiers
- Repress transcription
- Genome-wide pattern established at fertilisation
- Gene expression (transcription)
- Responds to environmental cues (cellular and external)
Characterised by complex interactions of DNA methylation, chromatin remodellin complexes, histone modifications, histone variants, histone modifying enzymes etc.
What is differential gene expression?
Biochemical process that determines which genes respond o which signals or triggers depending on the conditions
In time (temporal):
- Development (i.e. embryos vs adults)
- In response to hormones, infection, other signals
Spatially:
- Different tissues/cells express different genes (e.g. brain vs liver)
What happens if gene expression isn’t regulated?
- Metabolic disease
- Metastasis
- Congenital disorders
- Cancer
