B1.2 Flashcards
Structure of DNA
Made out of, what those made out of, what they do etc
- DNA are made up of lots of small units called nucleotides, making DNA a polymer.
- these nucleotides are made up of phosphate - deoxyribose sugar- and a different base each time, which could be A T C or G.
- nucleotides form a strand. DNA is made up of two of these strands twisted together to form a DOUBLE HELIX, and these stands are joined together BY :complementary base pairing
- short sections of double helix dna that code for a characteristic like eye colour are called GENES.
- long molecules of DNA are called CHROMOSOMES, and we have 23 pairs of these…
- size is : nucleotide, gene, chromosome, nucleus cell
Why does complementary base pairing need to happen?
This ensures the strands are tightly wounded together
Transcription how a copy of DNA is made : protein synthesis
What is IMPORTSNTNTO REMEBER ABOUT COMOLEMENTWRH BASE PARIJTN IN MRNA!!!
-DNA in nucleus too big to leave cells, so a copy of DNA called mRNA is made in the DNA, and this moves out to the cytoplasm where proteins are synthesised.
1) DNA around a gene unzips, exposing the bases on a strand so it can be used as a TEMPLATE.
2) free nucleotides in the nucleus complementarily bad pair with the exposed bases. However, there is no thymine in mRNA, so Uracil is used. So it is A-U, T-A, C-G
3) when complete, the mRNA detaches itself from the DNA template, and the DNA ZIPS together again
4) mRNA can now leave the nucleus, and it travels to the ribosomes in the cytoplasm for translation.
URACIL
Translation: how the mRNA codes for a whole protein
1) the mRNA is threaded through a ribosome, which ‘READs’ the nucleotides on the MRNA. It reads it in groups of three, called CODONS (base triplets).
2) each codon codes for a specific amino acid, and different combos of codons give different amino acids. Carrier molecules bring and add amino acids to the chain of amino acids.
3) once all codons are read, amino acids form bonds and this is now a protein. THE SEQUENCE of amino acids determine the shape and fold of the protein, which in turn determines the function of the protein.
4) for example, an active site,
What happen if a mutation occurs in a gene?
If a mutation occurs in a or section of itgene, BASES may be added, deleted or changed (swapped for another base).
- sequences of bases are changed so during transcription the wrong bases may have been copied, causing a coding of wrong amino acids during translation
Wrong sequence of amino acids can change the proteins shape, and if it is an enzyme- this can be a problem as it won’t be able to bind to a substrate and catalyse. (This can cause problem like phenylketonuria, where phenylalanine can’t be broken down in the bran and cause brain damage).
- however sometimes a change of bases result in the same amino acid being produced, resulting in nothing happening.
What about mutation occurring in non coding section.
Some bases before a gene, which actually tigger the process of transcription to take place for that gene. If a mutation occurs here, then the entire gene may not be transcribed into mRNA AT ALL, resulting in no protein being made, or the gene may transcribe too much, causing in too much of a protein being made- a tumour.
Mutations basically in non coding affect whether the gene becomes expressed, and therefore whether it gets synthesised or not.
What are enzymes? Why we need them.
Enzymes are biological catalysts- (AND PROTEINS) this means they speed up reactions with out being used up, and are bilogical so it happens in our body. THIS MEANS they can then catalyse another reaction of the same type after used,
(We need it because reaction in body too slow- can be increased be heating up but that increases reaction of bad that we don’t want too, and damages cell walls. With enzymes you can have specific reactions speeded up and cell wall no break)
- Enzymes and substrate form an ENZYME- SUBSTRATE complex. Reaction carried out quickly and then it moves in. They can be used in our body to build larger molecules from smaller like protein synthesis , or break larger ones to smaller like in DIGESTION
Lock and key hypothesis
Enzymes work by binding with a substrate at mit’s active site. Each enzyme can only bind with one substrate- meaning enzymes are highly specific as the substrate must fit exactly inside the active site to by catalysed, just like how a key must exactly fit into a lock to unlock.
Tempersture enzymes
At higher temperatures, enzymes and substrate molecules move faster and collide more - leading to in increase of reaction.
However enzymes work at an optimum temperature (37 in human). If it goes past this the amino acids in the chains start to unravel. This changes the shape of the active site, meaning a substrate can no longer bind to the enzyme and the rate of reaction DECREASES. The enzyme is now denatured, but only once all the enzyme MOLECULES ARE DENATURED DOES THE RATE OF REACTION STOP.
Change is also IRREVERSIBLE.
- graph goes up to w maximum, then decreases to a stop, gradually then
Others like pH and concentrations
Enzymes have optimum pH, increase until they reach, after that it unravels and denatured so reaction decreases till it stops.
- concentration: if you increase the ENZYME concentration , the relate of reaction will increase until a point where all the substrates have been catalysed, after that reaction just stops. Graph rises then completely drops
- if you increase SUBSTRATE molecules concentration , then the rate of reaction will increase to a maximum, where after that, more substrate molecules will no affect it as all the enzymes are being used, and so graph rise then plateaus .(saturation)
Enzyme + substrate
Enzymes- substrate complex
