the 1st unicram (3)

Question 1

ATP?

Answer 1

Consists of nuceloside joined to 3 phosphates
Universal energy currency in all living organisms
Soluble
Unstable

Question 2

What reaction is the hydrolysis of ATP?

Answer 2

Exergonic reaction

Question 3

Then pathway of ATP hydrolysis?

Answer 3

AMP –> ADP –> ATP

production of ATP is an endergonic reaction (requires energy)

Question 4

DNA extra information

Answer 4

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

Question 4

DNA information

Answer 4

• Anti-Parallel double helix
• Sugar Phosphate backbone joined by covalent phosphodiester bonds
• Nitrogenous base is joined to deoxyribose sugar via a glycosidic bond

Question 5

Histones information?

Answer 5

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

Question 6

Nucleosome information?

Answer 6

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

Question 7

Functions of Histones?

Answer 7

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

Question 8

Gene structure?

Answer 8

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

Question 9

Purine and Pyrimidine

Answer 9

Purine:
Guanine
Adenine

Pyrimidines:
Uracil
Cytosine

Question 10

Types of RNA

Answer 10

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

Question 11

Transfer RNA?

Answer 11

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

Question 12

Cell cycle phases

Answer 12

Metaphase:
Prophase,metaphase,anaphase,telophase
Cytokinesis

Interphase:
G1- growth phase
S - Synthesis Phase
G2 - growth phase
G0 - resting stage

Question 13

Purpose of G1?

Answer 13

Prepares cell for division,
protein synthesis
growth
organelle production

Question 14

Purpose of S?

Answer 14

Synthesis phase,
semi conservative replication of DNA occuirs

Question 15

Purpose of G2?

Answer 15

Final preparation for mitosis,
Nuclear envelope gets formed and encloses the nucleus
More synthesis of molecules and growth
Cell is prepared for division

Question 16

Purpose of G0?

Answer 16

Cells rest
Old and damaged cells are destroyed
Cell repair

Question 17

How are cell cycle checkpoints controlled?

Answer 17

Levels of cyclins, proteins produced by enzymes

Question 18

Where are the checkpoints?

Answer 18

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

Question 19

Prophase?

Answer 19

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)

Question 20

Metaphase?

Answer 20

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

Question 21

Anaphase?

Answer 21

Sister chromatids seperated as the spindle fibres contract, chromatids pulled back towards the poles

Question 22

Telophase?

Answer 22

Chromatids arrive at poles, become chromosomes
DNA decondenses
Telophase begins when nuclear membrane reforms
Spindle fibres break down
Nucleolus reforms

Question 23

Cytokinesis?

Answer 23

After nuclear membrane reforms, cytoplasm cleaves, two new genetically identical cells are formed

Question 24

what does Mitosis produce?

Answer 24

Produces 2 genetically identical cells with half the DNA and the same number of chromosomes as the parent cell

Question 25

What does Meiosis produce?

Answer 25

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

Question 26

What happens in PMAT 1 meiosis?

Answer 26

Generates variation Reduces the chromosome number to the haploid

Question 27

Prophase I?

Answer 27

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

Question 28

What is crossing over?

Answer 28

Exchange of genetic material at the chiasmata

Question 29

Metaphase I?

Answer 29

Random assortment occurs of homologous chromosomes Homologous pairs attach to the equator of the spindle

Question 30

Anaphase I?

Answer 30

Spindle fibres contract Homologous chromosomes seperate and move back towards the poles

Question 31

Telophase I and cytokinesis?

Answer 31

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

Question 32

Prophase II?

Answer 32

Mitotic division Seperates chromatids to produce 4 haploid cells

Question 33

Metaphase II and Anaphase II?

Answer 33

Spindle forms at right angles to orignial cell division Independant assortment also occurs at metaphase II, greater genetic variation

Question 34

Telophase II and cytokinesis?

Answer 34

Nuclei reform Cytoplasm cleaves 4 cells produced

Question 35

Transciption?

Answer 35

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

Question 36

Initiation for transcription?

Answer 36

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

Question 37

What is elongation for transcription?

Answer 37

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

Question 38

What is termination for transcription?

Answer 38

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

Question 39

What is translation?

Answer 39

Translates the strand of mRNA into a polypeptide chain Happens on the ribosomes

Question 40

What is charging of tRNA?

Answer 40

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

Question 41

What is the process of initiation for translation?

Answer 41

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

Question 42

What happens after Elongation for translation? (termination)

Answer 42

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

Question 43

Replication of DNA - the enzymes

Answer 43

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

Question 44

Process of DNA replication?

Answer 44

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