Lecture 1 - Human Genome Organization Flashcards
(40 cards)
What does genome refer to?
The genetic material in an organism
What does the genome comprise of in eukaryotes?
- comprised of both nuclear + mitochondrial genomes
Describe the following regarding the nuclear genome :
- Location
- DNA copies
- Genome structure
- Genome size
- Number of genes
- Coding region (%)
- Mode of inheritance
Location : Nucleus
DNA copies: 2 copies of 23 chromosomes per cell
Genome Structure: Linear DNA
Genome size: 3.2 x 10^9 base pairs
Number of genes: 30,000
Coding region : 2% ( 98% Non-coding )
Mode of inheritance : Nuclear DNA inherited from both mother & father (diploid)
Describe the following regarding the Mitochondrial genome :
- Location
- DNA copies
- Genome structure
- Genome size
- Number of genes
- Coding region (%)
- Mode of inheritance
Location : Mitochondria
DNA copies : Several copies of mt-DNA (2-10) per mitochondrion. Each cell contains multiple mitochondria, therefore each cell estimated 1,000-10,000 copies of mt-DNA.
Genome structure : Circular DNA
Genome size : 16,569
Number of genes : 37 genes
Coding region (%) : 97 ( 3% non-coding )
Mode of inheritance : Inherited only from mother (Haploid)
Describe what a Genome is :
- Total DNA content in a cell
- Contains all DNA including protein coding genes
- Each organism has one genome
- Study of properties of the genome is known as genomics
Describe what a Gene is :
- Segment of a total DNA molecule
- Only contain protein coding DNA
- Thousands of genes present in an organism
- Study of properties of genes known as genetics
Describe the structure of the human genome:
- Two nucleotides linked together by equal covalent bonds between the sugar of one nucleotide & phosphate group of another.
- many nucleotides joined together this way to form one strand of DNA
- DNA molecules consist of two strands of nucleotides wound together into a double helix
- Hydrogen bonds link the two strands together
- Complementary base pairing ( A-T & C-G ) occurs between the two strands
- The two strands run anti parallel ( 5’ to 3’ on one stand & 3’ to 5’ on the other )
What is Chargaff’s rule?
- A (30.9%) = T (29.4%)
- C (19.8%) = G (19.9%)
- Purines = Pyrimidines
What is the size of the DNA per cell? And what can it be divided into?
- 2 meters of DNA
- 46 human chromosomes
- 3 billion subunits/base pairs
- Approx 30,000 genes
How are such large DNA fibres compactly packaged in a small nucleus?
- Linear chromatin (DNA) fibres are tightly packed with Histone (H2A, H2B, H3 & H4) proteins.
- Dimers of histone proteins first form an octamer protein complex.
- The octamers bind & wrap the DNA around twice
- Each complex of Histone proteins & DNA wrapping around them is called nucleosomes
- Nucleosomes are separated by a 30-bp linker DNA
- Histone H1 binds on the linker site & protects the nucleosomes from becoming a mess/tangle
- All the nucleosomes condense further to form a loop like structure
- This loop structure further coils & gets denser to form a sister chromatid as seen in metaphase.
What occurs during the mitosis cell division & in which phase precisely?
- Metaphase stage
- Linear DNA packing w/ histone proteins
- Formation of a supercoiled sister chromatid
What is the significance of the Metaphase Chromosomes? Give an example.
- Used in karyotyping
- to identify chromosome number & structural abnormalities
- XO, XXY which is translocation error
Describe the Denaturation of the DNA double helix :
- When a double stranded DNA in solution is heated, the H-bonds holding the two strands together start breaking
At what temp. does denaturation occur? What does the particular temp. depend on?
- Denaturation of DNA at a particular temp depends on G-C & A-T content of DNA
- DNA containing A-T base pairs melts @ 70C due to weaker 2H bonds
- DNA containing G-C base pairs melts @ over 95C due to stronger 3H bonds
- Temp. where DNA strands half denatured are called melting temperature
- Melting temp. varies according to each organisms DNA based on their G-C / A-T contents.
Describe the Renaturation of DNA double helix :
- When the denatured DNA in solution is cooled down, complementary single strand DNA can reform into double stranded DNA with H bonding
- Must be in presence of water
- 37C
What are the significances of the denaturation and renaturation properties of DNA ?
- Used in experiments such as Hybridization & Polymerase Chain Reaction (PCR)
Describe the steps of hybridisation & why it is performed :
- Experiment performed to identify DNA homologous between two diff. organisms or their genes of interest.
1. Heat to separate strands (Denaturation)
2. Combine single strands of DNA
3. Cool to allow renaturation of double stranded DNA (Renaturation)
4. Determine degree of hybridization
What are the 3 degrees of hybridization?
Complete hybridization : organisms identical
Partial hybridization : Organisms related
No hybridization : Organisms unrelated
Describe what PCR does :
- Uses denaturation & renaturation properties of DNA
- to help amplify target DNA sequences in large quantities
Describe the typical structure of a 5’ to 3’ eukaryotic gene :
- Promotor region
- Transcription Initiation site
- 5’ untranslated region (5’-UTR)
- Translation start codon (ATG)
- Exons (Coding)
- Introns (Non-coding)
- Translation stop codon
- 3’ Untranslated Region (3’-UTR)
- Transcription termination site
What is the big difference between eukaryotic and prokaryotic gene structures?
Eukaryotic genes contain Introns.
Prokaryotic genes do not contain introns.
How do eukaryotic mRNA differ from prokaryotic?
- Eukaryotic mRNA is monocistronic. One mRNA is transcribed & translated into a protein.
- Prokaryotic mRNA is polycistronic.
One mRNA is transcribed & translated into multiple proteins.
Recall the sections & percentages of the entire genome :
.
What are Satellite or Tandem repeat sequences in the human genome?
- Satellite DNA belong to non-coding tandem repeats DNA sequences
- Repeated many times but always adjacent to each other
- DNA repeat length ranges from 100 to 100,000 times
- DNA repeat sequence size ranges from 1 to 300 bases
- Due to being non-coding, satellite DNA mostly located in the heterochromatin region of the human genome i.e TELOMERES & CENTROMERES
