GENETICS - Basics Flashcards
What is the process of DNA replication (4)
- DNA helix (parent strand) unwound by DNA helicase to form two single strands (templates)
at the replication fork - DNA polymerase adds nucelotides to these templates to allow new DNA leading strand to grow in 5’ to 3’ direction
- DNA lagging strand formed by discontinuous short nucleotide strands called Okazaki fragments by a different DNA polymerase which is formed in the 3’ to 5’ direction
- Thees are joined together by DNA ligase
What is transcription? What enzyme is involved?
DNA code is read in nucleus and complementary messenger RNA is produced, which leaves for the cytoplasm for protein synthesis.
RNA polymerase in a 5 prime to 3 prime direction
What is the structure of mitochondrial DNA? What type of inheritance? Which genes does it code for?
- Circular double stranded-DNA
- Inherited from mother
- Encodes 37 genes that produce structural RNA (22 tRNA, 2rRNA) & Proteins of electron transport chain (complex I, III, IV and V)
What is the relation between histones and DNA?
histones are alkaline positively charged proteins, allow them to interact with negatively charged DNA
Which is the short arm chromosome and which is the long arm chromosome?
p - petit
q - long
What is the structure of a nucleotide (3)
- Deoxyribose (pentose sugar)
- Nitrogen base (purines and pyramidines)
- Phosphate Group
How are adjacent nucleotides linked to each other?
How are the DNA strands linked to each other?
- 3’ to 5’ phosphodiesterase bond
- Hydrogen bonds between bases.
DNA complexes are called?
Histones
Histones are found as an octomer to form a nucleosome. They are packed together to make chromatin.
Chromatin fibre pack together to form a chromosome.
Whats the difference between euchromatin and heterochromatin? (2)
- Euchromatin is less densely packed than heterochromatin
- Euchromatin contains acetyl group
How long does a cell cycle last?
Usually 24 hours
What is the G0 stage?
Cell is quiescient, some cells permanently stopped in G0
What is the M stage?
Mitosis - occupies one hour
What happens in G1 stage?
Biosynthetic activity, cellular contents are duplicated (excluding chromosomes)
What happens in S phase?
DNA synthesis and chromosomal replication to form two daughter chromatids (6-8 hours)
What happens in G2 stage?
Second gap phase with preparation for division (cell doubles mass, chromosome checks for errors)
What are the four stages of mitosis?
Prophase
Anaphase
Metaphase
Telophase (Cytokinesis)
What happens in prophase? (4)
- Nucleolus disappears
- Chromatin condenses into chromosomes
- Separation of centrosomes
- Formation of mitotic spindle
What happens in metaphase?
chromosomes align in the equatorial plane
What happens in anaphase? (3)
- Centromere divides with chromatid separation at the centromere
- Chromatids move to the opposite poles of the cell
3.Unattached microtubules push against each other to elongate cells
What happens in telophase? (4)
- New nuclear envelope forms
- Chromosomes unfold back into chromatin
- Nucleolus reappears
- Cells continue to elongate
What happens in cytokinesis?
Division of cytoplasm
What are the role of cyclins in the cell cycle?
Regulatory subunits within cells which regulate cyclin-dependent kinases (CDKs)
they drive the cell through stages of the cell cycle via phosphorylation of protein substrates
Whats the difference between mitosis and meiosis?
see picture
Which is the most error prone phase in meiosis?
Anaphase I
What are the steps involved in protein transcription?
Initiation
1. Binding of transcription factors to promoter sequence in DNA (TATA box)
- RNA polymerase binds to promoter and separates DNA strands
Elongation
1. RNA polymerase along the DNA template strand adds complementary RNA nucleotide to the 3’ end of the RNA strand.
- The RNA molecule is made from the 5’ end to the 3’ end
Termination
3. RNA polymerase keeps transcribing until meets termination signal,
What three processes are involved in pre-mRNA processing?
Where does it occur?
- Addition of 5’ cap to the beginning of RNA (7-methylguanine nucleotide addition)
- Addition of 3’ poly A nucleotide tail to end of RNA (aids transport and provides stability)
- RNA splicing - removal of introns at the spliceosome and pasting together of exons
This occurs in nucleus - leaves once becomes mature and goes towards ribosomes for translation.
What is the process of translation?
Initiation
1. Start codon (AUG - methionine) is recognised
2. mRNA at 5’ end binds to small 40s subunit of ribosome, then large 60s subunit binds to make initiation complex.
Elongation
1. tRNA with initiator is attached to P site of ribosomal unit - tRNA/mRNA linkage is catalysed by initiation factor 2
- new tRNA with anticodon attaches to complementary codon of mRNA (amino acid is on other end of anticodon).
- Hydrogen bonds form between the two amino acids
- Once bond has formed, empty tRNA exits P site and ribosomal unit translocates one unit across to next codon and process repeats.
- Polypeptide chain is built from N terminal to C terminal
Termination
1. Stop codon enters A-site - no tRNA instead it is a release factor binds to A site
- This blocks further tRNA from binding and releases polypeptide chain into cytoplasm
What are histone proteins?
Histones are proteins that have DNA wound around it, they are influenced by environmental change and dictate which DNA parts are open for transcription –> CONTRIBUTES TO EPIGENETICS.
What is the Hardy Weinburg Equilibrium?
describes the constancy of gene frequences from one generaton to the next
What is the criteria for Hardy Weinburg principle to apply? (4)
- Absence of mutation
- Absence of genetic drift
- Absence of natural selection
- Randomly breeding population
Which bases are purines?
double ring structure.
*PURE AS GOLD
Adenine
Guanine
Hypoxanthine
Which bases are pyrimidines?
Single ring structure
CUT THE PYRAMID
- Cytosine
- Thymine (DNA)
- Uracil (RNA)
What is the process of viral replication?
What is the difference between DNA virus and RNA virus in replication
Replication occurs in host cell nucleus or cytoplasm
- Adsorption - attachment of virus particle to cells by (1) Collision (2) Electrostatic attachment (3) Host cell receptor
- Penetration - fusion of viral envelope with cell membrane
- Capsid removal by host cells
- Nucleic acid replication
DNA virsues replicate in nucleus of host cells and create messenger RNA
RNA virus replication occurs in cytoplasm, and uses reverse transcriptase to make DNA from RNA template –> RNA virus unable to use host cell enzymes and uses reverse transcriptase to synthesis own proteins
When does recombination occur during meiosis?
Crossing over of non-sister chromatids occurs in prophase I of meiosis.
Which amino acids are positively charged? (2)
Which amino acids can be encoded only by one codon (2)
Which amino acid is the start codon (1)
+ve amino acids:
Arginine, Lysine –> found in histones.
one codon amino acids:
Tryptophan (TGG) and methionine (ATG/AUG)
start codon amino acid: AUG (methionine)
Where does histone modification occur?
post-translational modifications occur on the histone tail.
What molecule is responsible for mitochondrial DNA replication? What gene is responsible and where is it found?
What conditions is this related to?
DNA polymerase gamma.
Found on POLG gene on chromosome 15. Mutations here can cause
1. progressive external ophthalmoplegia
2. Alper’s syndrome.
What do these terms mean:
1. Metacentric
2. Acrocentric
Which chromosomes are involved in either?
Metacentric: chromosomes have centromeres located centrally, and have two arms of roughly equal length (chromosome 1 and 3)
Accrocentric: Centromere is near terminal end, giving rise to p and q arms. (Chromosome 13, 14, 15, 21 and 22).
What is the role of ubiquitin?
What is the role of proteosomes?
What is the role of lactacystin?
Ubiquitin tags and marks unwanted proteins –> plays a role in destroying phosphorylated cyclins and CDKs.
Proteosomes target ubiquitin tagged proteins and cleave them into peptides
Lactacystin inhibits proteosomes.
