the 1st unicram (3) Flashcards
ATP?
Consists of nuceloside joined to 3 phosphates
Universal energy currency in all living organisms
Soluble
Unstable
What reaction is the hydrolysis of ATP?
Exergonic reaction
Then pathway of ATP hydrolysis?
AMP –> ADP –> ATP
production of ATP is an endergonic reaction (requires energy)
DNA extra information
Triplet code: Each 3 bases code for an animo acid
Degenerate code: (Stop and start codons), Amino acids coded for by more than one codon
Non overlapping code: Each base is only used once in a codon
DNA information
- Anti-Parallel double helix
- Sugar Phosphate backbone joined by covalent phosphodiester bonds
- Nitrogenous base is joined to deoxyribose sugar via a glycosidic bond
Histones information?
Proteins that bind to DNA, they maintain shape and regulate gene activity
8 histones form a nucleosome with DNA
Highly basic protein, abundant in lysine and arginine
Nucleosome information?
Single nucleosome consists of 150 base pairs of DNA sequence wrapped around a core of histone proteins
When forming a chromosome, the nucleosome repeatedly fold in on themselves to tighten and condense the packaged DNA
Functions of Histones?
DNA packaging and nucleosome formation
- Histones are responsible for packaging and condensing long DNA strands into nucleosomes. Nucleosomes compact, scaffold, organise DNA into chromatin
- Allows DNA to fit in the nucleus, prevents tangling and damage of DNA
Gene regulation and DNA replication
- Changes like methylation, acetylation and phosphorylation of histones modulate chromatin structure and affectn gene expression
Epigenetic Inheritance
- Change in histone modifications can be passed on to daughter cells during cell division, contributes to Epigenetic Inheritance
DNA Repair
- Phosphorylated at sites of DNA damage, marks it for repair
Chromosome Segregation
- Histones ensure accurate segregation of chromosomes into daughter cells
Maintaining Genome Integrity
- Histones protect integrity of the geneome, prevents DNA to damaging agents
Scaffolding for Protein binding
- Histones provide a scaffold for the binding of proteins involved in transcription, DNA replication and repair processes
Gene structure?
3 regions: promoter, coding region, termination sequence
(coding regions are not continuous in eukaryotes)
Made up of areas that are trasncribed into mRNA (Exons)
Which are interrupted by stretches of DNA that do not appera in mature mRNA (Introns)
genes are a minority of total DNA
more than 98% of the human genome consists of noncoding DNA
Between genes there are vast stretches of untranscribed DNA that play a structural role
Purine and Pyrimidine
Purine:
Guanine
Adenine
Pyrimidines:
Uracil
Cytosine
Types of RNA
mRNA: Messenger RNA, single stranded, variable length
rRNA: Ribosomal RNA, formes ribosomes.
Prokaryotes
Ribosomes have an exit, peptidyl and acceptor site to link amino acids together to create polypeptides
Transfer RNA?
Carries amino acids to a ribosome complex with help of aminoacyl-tRNA synthetase
aminoacuyl-tRNA synthetase load appropriate amino acid onto a free tRNA to form aminoacyl-tRNA
Amino acid depends on the mRNA codon and anticodon arm of tRNA, whichn is complementary to the mRNA codon
Cell cycle phases
Metaphase:
Prophase,metaphase,anaphase,telophase
Cytokinesis
Interphase:
G1- growth phase
S - Synthesis Phase
G2 - growth phase
G0 - resting stage
Purpose of G1?
Prepares cell for division,
protein synthesis
growth
organelle production
Purpose of S?
Synthesis phase,
semi conservative replication of DNA occuirs
Purpose of G2?
Final preparation for mitosis,
Nuclear envelope gets formed and encloses the nucleus
More synthesis of molecules and growth
Cell is prepared for division
Purpose of G0?
Cells rest
Old and damaged cells are destroyed
Cell repair
How are cell cycle checkpoints controlled?
Levels of cyclins, proteins produced by enzymes
Where are the checkpoints?
At the boundary of G1 and S, ensures cells aren ready to undergo DNA replication, nutritions checked.
At the boundary of S and G2, DNA is checked to ensure there are no mutations
At the boundary of G2 and M
Final checkpoint is at telophase , to ensure chromosomes are segregated properly before divison
Prophase?
DNA condenses, shortens, thickens and becomes two chromatids joined by a centromere
Centrosomes migrate to the poles and initiate spindle formation
(centrosomes are made up of two centrioles at right angles to one another)
Metaphase?
Two stages, prometaphase and metaphase:
Prometaphase:
Nuclear envelope breaks down and microtubules attach to chromosomes
During this, microtubules grow and shrink until the ends contact chromosomes
Metaphase:
Changes to spindle occur, microtubules lengthen and shorten until chromosomes align along the centre of the cell
Anaphase?
Sister chromatids seperated as the spindle fibres contract, chromatids pulled back towards the poles
Telophase?
Chromatids arrive at poles, become chromosomes
DNA decondenses
Telophase begins when nuclear membrane reforms
Spindle fibres break down
Nucleolus reforms
Cytokinesis?
After nuclear membrane reforms, cytoplasm cleaves, two new genetically identical cells are formed
what does Mitosis produce?
Produces 2 genetically identical cells with half the DNA and the same number of chromosomes as the parent cell
What does Meiosis produce?
Produces variation and reduces the chromosome number to the haploid so it can be made into a diploid on fertilisation
Produces 4 genetically different cells with half the chromosome number and 1/4 of the DNA of the parent cell
What happens in PMAT 1 meiosis?
Generates variation
Reduces the chromosome number to the haploid
Prophase I?
5 Phases:
Leptotene: Chromatin starts to condense and form chromosomes
Zygotene: Homologous chromosomes come together in homologous pairs
Pachytene: Cross over of non-sister chromatids
Diplotene: Formation of chiasmata
Diakinesis: Chromosomes move apart
What is crossing over?
Exchange of genetic material at the chiasmata
Metaphase I?
Random assortment occurs of homologous chromosomes
Homologous pairs attach to the equator of the spindle
Anaphase I?
Spindle fibres contract
Homologous chromosomes seperate and move back towards the poles
Telophase I and cytokinesis?
Nuclear membrane reforms and cytoplasm divides to produce two haploid cells, each with half the chromosome number and half the DNA of the parent cells
Prophase II?
Mitotic division
Seperates chromatids to produce 4 haploid cells
Metaphase II and Anaphase II?
Spindle forms at right angles to orignial cell division
Independant assortment also occurs at metaphase II, greater genetic variation
Telophase II and cytokinesis?
Nuclei reform
Cytoplasm cleaves
4 cells produced
Transciption?
Occurs in the nucleus of eukaryote and cytoplasm of prokaryotes
Produces pre-mRNA
Starts with initiation where DNA unwinds
One strand acts as the template, other is non-coding
Initiation for transcription?
Transcription gets catalysed by the enzyme RNA polymerase. Attaches and moves along the DNA molecule until it recognises a promoter sequence
Transcriptiion starts when 6 general transcription factors come together at the promoter region of a gene.
Next, one or more transcriptional activator proteins bind to an enhancer region on the DNA
When the activators bind to the enhancer DNA, they attract a mediator complex of proteins which attract RNA polymerase for transcription to begin
What is elongation for transcription?
Occurs in a transcription, where the two strands of DNA are seperated and the RNA nucleosides come and base pair with the template strand
Triphosphate ribonucleosides join to form a strand of pre MRNA
Breaking of the phosphodiester bond between nucleotides releases the other two phosphate groups, provides energy for reaction to occur
What is termination for transcription?
Elongation continues until RNA polymerase encouinters a stop sequence
mRNA now needs to be stabilised so it doesn’t become damaged as it leaves the nucleus and travels through the cytoplasm to the ribosomes.
Polyadenylation occurs, 250 adenine nuleotides get added to the strand to stablalise the mRNA.
At the end of the new strand, a methylated guanine cap is added which is essential for translation to occur
What is translation?
Translates the strand of mRNA into a polypeptide chain
Happens on the ribosomes
What is charging of tRNA?
Aminoacyl tRNA synthetases connect a specific amino acid to the amino acid binding site on then tRNA, catalyses the formation of a covalent bond
tRNA said to be charged once the amino acid is added
What is the process of initiation for translation?
Charged MET tRNA is situated on P site
The next charged tRNA with its amino acid comes down and attaches to A site
Peptide bond formed between two amino acids
Ribosome shifts along, tRNA carrying MET is now uncharged and goes to the E site and leaves the ribosome
The tRNA on A site is now on P site, frees A site for the next charged tRNA
Whole process helped by proteins called elongation factors which are bound to GTP and break the triphosphate bond, releases the energy to allow the polypeptide chain to elongate
What happens after Elongation for translation? (termination)
Elongation occurs until a stop codon is reached
This doesn’t code for tRNA
At this point a protein release factor binds to the A site and releases the polypeptide chain
Replication of DNA - the enzymes
Semi-conservative replication produces a new helix with one new and one original strand
DNA unwinds at the replication fork, each strand becomes a template strand and the new strand thatn will form is the daughter strand
DNA helicase separates the parent strands (Breaks hydrogen bonds between complementary base pairs)
Single strand binding protein attaches to the strands and stops them re-annealing
Topoisomerase moves up the helix, relieves the stress of DNA unwinding
DNA polymerase catalyses the formation of a new strand
Process of DNA replication?
RNA primase produces short strand/primer to start the process
DNA polymerase then takes over and adds nucleotides to 3’ end of replicating strand , can only add nucleotides to the end of the 5’ strand
Triphosphate nucleosides get added when the inner most inter phosphate bond gets broken, and the two phosphates are released. This provides energy for the joining of the nucleotides
replication is continuous in leading strand, while in lag strand it is discontinuous and makes fragments which are joined by DNA ligase
Lagging strand must loop round to be replicated
Polymerase proofreads the forming strands
