The human genome Flashcards
What is the genome?
All the genetic information of an organism
How many nucleotides making up coding genes in humans?
3.2 billion make up 20,000
What is a genome divided up into?
2 sex chromosomes
44 (22 pairs) of autosomes
37 genes on circular mitochondrial chromosomes
Why do mitochondria have their own separate set of genes?
13 out of 37 provide instructions for making enzymes
What is a nucleotide made of?
Nitrogenous base
Phosphate group
5 carbon sugar (deoxyribose)
What chemical bonds hold DNA together?
Covalent phosphodiester bonds between 5’ of one sugar and 3’ of another
Hydrogen bonds between base pairs
How is DNA packaged into the nucleus?
1-DNA (negatively charged) bound to histone proteins (positively charged) to make nucleosomes
2-Coil nucleosomes to form 30nm thick
3-Chromatin fibres assembled on a protein scaffold to form a chromosome
What is coding DNA?
codes for proteins
7 examples of non coding DNA
Genes for other RNAs
Promoter regions
Introns
Tandem repeats
Telomeres
Pseudogenes
Viral DNA
Junk DNA
What are Pseudogenes?
DNA sequence that resembles a gene but has been mutated into an inactive form over the course of evolution
What are tandem repeats?
repeated short DNA sequences, occur due to polymerase “slippage”
What is the role of coding RNA?
Messenger mRNA (DNA-mRNA and mRNA- proteins)
Viral genomes (RNA how some viruses store genetic material)
What is the role of structural RNA?
Ribosomal rRNA (makes up ribosomes)
Transfer tRNA (carries amino acids to ribosome in translation)
What is the role of regulatory RNA?
microRNA (involved in post- transcriptional regulation of gene expression)
Xist (switches off one copy of the X chromosome in XX cells creating a Barr body)
What is the Sense/coding strand?
the stand (when read in the right direction) contains the specific code to make a protein, matches mRNA
What is the Antisense/ template strand?
the stand with the opposite sequence to the sense strand
Steps in DNA replication (leading strand)
- Unzip the double helix (DNA helicase)
- Attach a primer (primase enzyme)
- Add complementary nucleotides (DNA polymerase III adds nucleotides)
What prevents over coiling?
Topoisomerase
What direction are nucleotides added in?
5’ to 3’ direction and starts at primer
Steps in DNA replication (lagging strand)
-Unzip
- Add primer (DNA polymerase only works in one direction so primer adds close to helicase)
- DNA polymerase III add nucleotides in 5’3’ direction
- Helicase unzips more and process repeats
- Once replication is complete= lagging strand is a mess
What happens after DNA replication of the lagging strand?
- Made up of OKAZAKI FRAGMENTS
- Mix of RNA and DNA
- Primers from RNA are turned into to DNA using DNA polymerase I
- Gaps are stitched together by DNA ligase
What is PCR?
- Amplifies a DNA sample in a lab to allow us to perform genetic testing
What ingredients are added to PCR tube?
- The DNA sample from your patient
- Nucleotides
- Buffer solution
- Primers
- DNA Taq polymerase (heat stable DNA polymerase 1)
Steps in PCR
- Denaturation (94-95)
- Annealing (50-60)
- Extension/ Elongation (72)
Repeat approx 30 times, num of repeats depends on amount of DNA needed
Denaturation (95)
Heating to 95 seperates the two strands of double stranded DNA
Annealing (55-65)
Primers bind to single stranded DNA
Extension (72)
Taq DNA polymerase activity is optimum at 72 and new DNA is therefore synthesised during this phase
What is a Barr body?
An inactivated X chromsome in a female somatic cell
What is the function of the enzyme DNA telomerase?
To prevent the ends of chromosomes from degradation
What is semi conservative replication?
After replication each strand is made of half of the original strand
