DNA and Chromosomes Flashcards
What are the stages of Cell Cycle? (4)
- Mitosis and Cytokinesis (nuclear and cytoplasmic division)
- G1 phase - Growing proteins and organelles
- S phase - DNA replication of 23 pairs of chromosomes to 46 pairs
- G2 phase - preparation for
What are the 6 stages of Mitosis? (6)
(PMAT)
- Prophase
- Pre-metaphase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
Describe Prophase (3)
Prophase:
- Chromosomes condense chromatins to 2 sister chromatids joined at a centromere.
- Centrosomes migrate to end of the cell with spindles forming.
Describe Premetaphase and metaphase (3)
Premetaphase: Nuclear envelope starts to disappear due to phosphorylation.
Metaphase:
- Chromosomes line up in the middle of the cell.
- Spindle fibres attach at kinetochore in preparation for anaphase.
Draw and label a metaphase chromosome (2 sister chromatids joined together) (5)
Allocate:
- Telomere
- Centromere
- Short arm and long arm
- Kinetochore
- Spindle fibres
Describe Anaphase (2)
- The 2 sister chromatids are pulled apart by the microtubules towards centrosomes.
- Forming 2 chromosomes at each end.
Describe Telophase and cytokinesis (3)
Telophase :
- Chromosomes arrive at centrosome.
- Nuclear envelope starts to reform around chromosomes
Cytokinesis: Cytoplasm and cell membrane divides to form 2 new identical cells.
What proteins control are cell cycle checkpoints? (2)
- cyclins
- Protein kinases
Controlled by phosphorylation of kinase or cyclin complex.
Why are cell cycle checkpoints important? (2)
- Errors are checked for at G1, S, G2 or mitosis e,g damaged DNA, improper replication or poor attachment to spindles.
- Failure to check (stop, wait or go) leads to cancer.
How many base pairs are replicated in DNA, and at what accuracy and speed? (2)
- 6 billion base pairs
2. 100 nt/s accuracy and speed at multiple points and time about 1 hour.
Describe the steps of DNA Replication in Leading Strand (4)
- DNA chain in unwound by enzyme (topoisomerase)
- Helicase breaks hydrogen bonds between base pairs to form replication fork.
- DNA primase adds RNA primer.
- DNA polymerase binds to primer to add nucleotides from 5’ to 3’ end. This happens continuously in leading strand.
Describe replication in lagging strand (4)
- As lagging strand runs in opposite direction (3’ to 5’), nucleotides can only be added in fragments. (Okazaki fragments).
- DNA primase adds RNA primer.
- DNA polymerase attaches to primer, adding nucleotides to fill in gap to form okazaki fragment.
- DNA primase attaches further up line and repeats steps.
Describe final steps of DNA replication (3)
- Enzyme Exonuclease removes all RNA primers from both strands of DNA.
- Another DNA polymerase attaches to fill in gaps left with DNA.
- DNA ligase seals up fragments of DNA to form continuous strand.
Why is DNA replication called semi-conservative? (1)
It is made up of one conserved (old) strand of DNA and one new strand.
What is an example of a condition resulting from DNA helicase in DNA replication? (3)
Werner Syndrome (mutation in Helicase)
- Causes premature ageing
- Increase risk of cataracts, cancer, atherosclerosis etc.
How is accumulation of mutation prevented during Replication and in cell cycle? (2)
- DNA polymerase can proof-read during replication
- Excision repair systems in place throughout cell cycle (G1, S, G2 etc).
How does DNA repair occur? (4)
- Damage in strand in recognised by DNA polymerase
- DNA Nuclease removes damaged region
- DNA polymerase makes new strand using bottom as template.
- DNA ligase seals strand.
Examples of External sources that can cause DNA Damage?
UV, mutagenic chemicals.
Example of inherited disease characterised by problem with DNA repair? (4)
Xeroderma Pigmentosum (acute sun sensitivity, poor pigmentation, cancers at young age, degeneration, intellectual disability)
- It is Autosomal recessive disorder.
- Caused by two thymines bounded together.
How are mutations Characterised? (3)
- Effect on heritability (somatic or germline)
- Scale of mutation (chromosome or SNP)
- Effect on normal function (loss or gain of function)
How can single gene mutations occur and example of corresponding disease that could result? (3)
- Substitution (sickle cell anaemia) Loss of function
- Deletion (cystic fibrosis) loss of function
- Insertion (huntingtons disease) gain of function
Describe Sickle Cell (3)
- Substitution Mutation in Beta globin gene; loss of function mutation.
- Leads to change of tetiary structure of red blood cells, which do not survive as long and clog up capillaries
- Around 12,500 cases in UK
Describe Cystic Fibrosis (3)
- Deletion Mutation, 70% of patients share 3bp deletion in CFTR (cystic fibrosis transmembrane conductance regulator) or chr 7.
- Impairs chloride transport, cause build up of mucus in lungs that lead to infection.
- Loss of Function
Describe Huntingtons disease (3)
- Insertion mutation, CAG tri-nucleotide repeats >40. (carrier 36-39). Gain of function.
- Damages nerve cells in areas of brain
- Leading to uncontrollable muscular movements, loss of memory and depression, difficulties with speech and swallowing.
