IMMS: Week 3 Flashcards
Describe the process of DNA replication
- Topoisomerase unwinds DNA and DNA helicase separates DNA apart to expose two single DNA strands and create two replication forks. DNA replication takes place simultaneously at each fork.
- SSB’s coat the single DNA strands to prevent re-annealing or ‘snap back together’
- The primate enzyme then uses the original DNA sequence on the parent strand to synthesise a short RNA primer.
- DNA Polymerase begins to synthesise a new DNA (via complementary base pairing using free floating nucleotides) strand by extending an RNA primer in the 5’ to 3’ direction. Each parental strand is copied by one DNA polymerase
- As replication proceeds, RNAse H recognises RNA primers bound to the DNA template and removes the primers by hydrolyzing the RNA.
- DNA polymerase can then fill the gap left by RNAse H.
- DNA replication process completed when the ligase enzyme joins the short DNA pieces together into one continuous strand.
What are okazaki fragments
The short pieces of DNA that need to be joined together to form one continuous strand.
DNA vs RNA
- DNA is double stranded with a complementary chain. RNA is single-stranded
- RNA contains uracil as a base instead of thymine
Name the three types of RNA
- mRNA
- rRNA
- tRNA
Role fo mRNA
Conveys genetic information that will be translate into a protein
Role of tRNA
Delivers amino acids to RER during translation
Role of rRNA
Catalyses the formation of peptide bonds between the amino acids during translation.
Describe the process of transcription
- Transcription factors find their way to specific sequences on the 5 on the 5’ on the first exon - the promotor
- A ‘transcription complex’ forms around the TATA box (thymine,adenine, thymine, adenine) on the 5’ of the first exon.
- Topoisomerase unwinds the double helix by relieving the supercoils. DNA helicase then separates the DNA apart exposing the nucleotides. SSB’s coat the single DNA strands to prevent DNA re-annealing.
- Free mRNA nucleotides line up next to their complementary bases on the template strand/antisense strand of the DNA (U-T + C-G)
- RNA polymerase 2 joins the mRNA nucleotides to form antiparallel mRNA strands (5’ to 3’ remember) starting at the promoter.
- mRNA leaves the nucleus and attaches to an 80s ribosome.
- At the ribosome the mRNA sequence is used as a template to bind to complementary tRNA molecules at their anticodons (3 bases complementary to codon on mRNA).
- Ribosome reads mRNA codon by codon and amino acids are brought in by specific tRNA molecules
- Enzymes remove amino acid from tRNA and amino acids are linked together by a peptide bone creating a polypeptide chain - a protein
What are the stop codons in RNA
UAG
UAA
UGA
What part of the tRNA molecule carries the amino acid
its 3’
How are bases read
5’ to 3’
Do promotor sites code for proteins
No, they only act as binding sites
What part of the DNA are promotor sites found on
5’ end.
What is the start codon
AUG
Where is mRNA produced
Nucleus
How does the ribosome recognise the mRNA
from the CAP on the 5’ end.
What are exons
Parts of the DNA that will encode a part of the final mature RNA
What are introns
Non-coding parts of DNA which are removed from immature mRNA via SPLICING
What is the mRNA primary transcript
Single-stranded RNA chain which can then be used to produce tRNA, mRNA or rRNA
How does primary mRNA transcript become mature
Splicing
What is exon shuffling
This is where new genes are formed as two or more axons from different genes can be brought together to produce a new exon-intron structure
Three characteristics of the genetic code
Degenerate but unambiguous - Many amino acids can be coded for by different combinations of triplets but each codon specifies only one amino acid
Almost universal - All organisms use the same code
Non-overlapping and without punctuation - Codons do not overlap and each nucleotide is read once.
How is immunoglobulin production in normal macrophages stopped
The gene for producing immunoglobulins is stored as ‘heterochromatin’ so it isn’t being expressed
How is immunoglobulin production in normal B cells produced
Gene is placed in ‘euchromatin’ state so it can be transcript.
HINT: Eu means euphoric = free
What is the difference between euchromatin and heterochromatin
Heterochromatin is DENSELY packed
Euchromatin is very lightly packed
What molecule stops expression of genes
Repressors
How do repressors prevent expression of genes
Inhibit RNA polymerase binding
What is a ‘duplication’ mutation
Where genes or parts of a gene or a single base are duplicated
What is a deletion of a gene
‘out of frame’ deletion - A deletion in an amino acid that causes a frame shift and changes all bases downstream and thus the whole protein
‘in frame’ deletion - Where a CODON is removed (sequence of three bases) which does not alter the sequence of bases downstream (we get a milder disease)
What is a mutation of regulatory sequence
Coding sequence is intact but a mutation causes the gene to switch off or on
What external factors can cause DNA damage
Chemicals, UV and radiation
What is mismatch repair
Repairing insertions, deletions and mis-incorporation of bases during DNA replication
What is a mis-sense mutation
Where a single nucleotide change results in a codon that codes for a different amino acid (substitution) Which can result in a silent mutation or non-functional protein
Name an example of a disease which results from mis-sense mutation
Sickle cell disease
What is a non-sense mutation
Point mutation that produces a stop codon - results in incomplete and non-functional protein
What is a splice-site mutation
Affects the accurate removal of an intron
Enzyme no longer recognises the sequence so excision of intron does not occur - causes translation of the intron
How is huntington’s disease caused
Repeat of CAG several times in the FIRST PART OF THE CODING SEQUENCE
What is this type of mutation called
Expansion of a tai-nucleotide repeat
What is the normal range of repeats of a tri-nucleotide in a normal human
15-20
What is the consequence if a trinucleotide is repeated more than 36 times in the first part of the coding sequence
Develop huntington’s and onset of disease is earlier with more repeats
NOTE: less than 36 repeats causes no disease
Describe anticipation
Repeats get bigger of the tri-nucleotide when transmitted to the next generation resulting in earlier symptoms and greater severity
What is the aim of PCR
To synthesise fragments of DNA
What are primers
Short synthetic pieces of DNA that have complementary bases to DNA you are trying to synthesise/amplify
How long does one cycle of PCR take
5-20 minutes
What is homeostasis
It is the maintenance of an internal environment within a narrow range
Define autocrine
Chemical released from a cell into ECF that acts on the cell that produced it
Define paracrine
Chemical messengers involved in the communication between cells, released into ECF (travel short distances)
What is the difference between endocrine and paracrine
Hormones travel in the blood in endocrine whilst paracrine chemical messengers only travel in the ECF. Endocrine affects more things and travels further
What is a positive feedback loop
Amplification of a signal
What is the problem with negative feedback loops
Can get primary issues - Problems with the endocrine glands
Can get secondary issues - Problem lies with the pituitary or hypothalamus
What is a hormone
Molecules that act as a chemical messenger
Define serous effusion
Excess water in a body cavity
Define oedema
Excess fluid in intracellular tissue space (interstitial)
How is lymphatic oedema caused
Obstructions by a tumour
How is venous oedema caused
Due to increased venous pressure or venous obstruction from a thrombus
Define hypernatraemia
High sodium conc.
