Genes and Proteins - find more info in a level biology folder Flashcards
What are the 5 types of histones?
H1, H2A, H2B, H3, H4
What are the two types of chromatin?
Euchromatin and Heterochromatin
what are the general features of Euchromatin?
-lightly packed
-can be transcribed
-found in loops near the nuclear pore in parts of chromosomes that contain many genes
What are the general features of heterochromatin?
-densely packed
-found in parts of chromosomes where there are few, inactive or no genes
-not transcribed
-replicated late in s phase
-have reduced crossing over during meiosis
label a chromosome
(check screenshots in file folder)
Give the stages of the cell cycle
INTERRPHASE:
-G1 phase: interval between mitosis and DNA replication initiation
-G0 phase: cells stop dividing and are locked into phase
-S phase: synthesis - where DNA is replicated
-G2 phase - where cell growth continues and proteins are made up
M PHASE:
mitosis and cytokinesis
What are the two types of cyclins?
mitotic cyclins and G1 cyclins
Give the process of cell cycle regulation:
-at G2 Cdk phophorylates histones and other proteins
-cell accumulates mitotik cyclin
-mitotic cyclin binds to cdk to form MPF and so triggers mitosis
-MPF activates cyclin degrading protein causing G2 cyclin to be degraded ending mitosis
- at G1 checkpoint, G1 cyclin phosphorylates CDK and triggers the s phase
-cyclin degrading protein is activated and G2 is triggered
What is the cause for retinoblastoma?
mutation of the Rb1 gene on chromosome 13. Rb1 is a tumour suppressor and normally regulates cell growth and limits proliferation
what is carcinogenesis example in the eye
Retinoblastoma
what is retinoblastoma
A rare form of cancer which develops in the retina and is the most common malignant cancer of the eye in young children
what post translational modifications can occur?
-phosphorylation
-lipidation
-acetylation
-glycosidation
What are alleles?
Different forms of the same gene with small differences in DNA sequence that make up the phenotype
What are histones?
linear double stranded DNA that’s tightly coiled around proteins.
what is chromatin made up of
nucleosomes which are groups of 8 histones bound by DNA
what is critical during the s phase of the cell cycle?
Histone biosynthesis
What is the point of cell cycle regulation?
to prevent mutant cells from replicating and causing cancer
Where and what are the checkpoint in the cell cycle?
-G1 checkpoint: makes the key decicison on if the cell should divide
-G2 checkpoint: decided if mitosis should occur
-M checkpoint: triggers the cell to enter cytokinesis
What happens at interphase?
there is de-condensed chromatic in the nucleus
- nucleoli are visible
- the nuclear membrane is visible
- centrioles are present
- the DNA undergoes replication and the two chromosomes remain joined at the centromere
what happens at prophase?
chromatin condenses and chromosomes become visible
- nucleoli disappears
- the nuclear membrane disappears
- the centrioles move to the poles off the cell and each centriole forms spindle fibres to produce the spindle apparatus
- the chromosomes attach to the spindle fibres at their centromeres
What happens at metaphase?
- the chromosomes can be seen to be made of two chromatids
- the microtubules of the spindle apparatus are attached to the centromere of each chromosome
- the chromosomes are pulled along the spindle apparatus and arrange themselves across the equator of the cell
What happens at anaphase?
- the centromeres divide and the spindle fibres begin to shorten
- sister chromatids are pulled to opposite poles by the spindle fibres using energy from ATP
- the separated chromatids are now referred to as individual chromosomes
What happens at telophase and cytokinesis ?
- the chromosomes reach the poles and de-condense making them no-longer visible to leave the widely spread chromatin
- the spindle breaks down and the centrioles reappear
- the nuclear membrane and nucleoli reappear
- the cytoplasm divides in cytokinesis to form two identical daughter cells
What are the stages of meosis?
nterphase- homologous pair of chromosomes are replicated
Meiosis I - homologous pair of replicated chromosomes separate and the chromosome number is halved
Meiosis II - each of the sister chromatids separate to produce 4 haploid daughter cells
What are the steps in crossing over
- The chromatids of each pair become twisted around each other
- This causes tensions and so portions of chromatid break off
- The broken portions then rejoin with the chromatids of its homologous partner ( usually the equivalent portions of homologous chromosomes are exchanged)
- This causes new genetic combinations of maternal and paternal alleles to be produced
What are the steps of eukaryotic transcription?
. RNA polymerase binds to the region of DNA to be transcribed
2. The two strands here unwind and separate breaking the H bonds between complementary base pairs leaving both strands of the DNA molecule in the region of the gene exposed
3. One strand acts as a template strand to make mRNA
4. Activated RNA nucleotides in the nucleus are attracted to their complementary bases and H bond with their corresponding DNA nucleotides (A on DNA pairs with U on RNA)
5. RNA nucleotides align themselves along the DNA template strand as RNA polymerase moves along the template strand to form phosphodiester bonds between the adjacent RNA nucleotides
6. RNA reaches a specific termination sequence and it detaches and the process stops
7. The pre-mRNA has now been produced as the sequence of bases on the DNA molecule have been transcribed to a sequence of codons on the mRNA molecule
8. Introns are then removed through splicing and the exons join together resulting in the mature mRNA molecule which leaves the nucleus via nuclear pore
Give the steps of translation
- A ribosome attaches to the starting codon at one end of the mRNA molecule
- The tRNA molecule with the complementary anti-codon sequence moves to the ribosome and pairs up with the codon on the mRNA and this tRNA carries a specific amino acid
- The t RNA molecule with a complementary anticodon pairs up with the next codon on the m RNA and this t RNA molecule carries another amino acid
- The ribosome moves along the m RNA bringing together two tRNA molecules at any one time each pairing up with the corresponding two codons on the mRNA.
- The two amino acids on the tRNA are joined by a peptide bond using an enzyme and ATP which is hydrolysed to provide the required energy
- The ribosome moves on to the third codon in the sequence on the mRNA and so linking the amino acids on the second and third tRNA molecules
- As this happens, the first tRNA is released from its amino acid and is free to collect another amino acid
- The process continues with up to 15 amino acids added each second
- Once the ribosome reaches a stop codon, the polypeptide chain is complete
What bases are purines and what bases are pyrimidines?
Purines: A and G, each has a double ring
Pyrimidines: T,C and U, each has a single ring
What else do I need to go over?
biological molecules - nucleic acids from the a level biology folder
Give four features of mRNA’s structure
long stranded
- single helix
- made of a linear sequence of triplet codons
What is mRNA used for?
It acts as a templete for protein synthesis
How is mRNA’s structure adapted to its function?
Its information is stored in a linear sequence of triplet codons and the sequence of the codons determines the amino acid sequence of a specific polypeptide that’ll be made
What is ribosomal RNA?
A long , single stranded molecule that forms part of the structure of ribosomes
Give 5 features of tRNA
small molecule
- its single stranded and folded into a clover leaf
- each tRNA is specific to one amino acid
- its anti codon region forms complementary base pairs with a codon of the mRNA strand
- It contains complementary base pairs within the molecule
what is the central dogma of molecular biology?
the idea based on the principle that genetic info travels from DNA to RNA and finally to protein translation
