B13 - Reproduction PART 2 OF ACC VERSION Flashcards
How do the cells read the DNA sequences ?
The cells read the DNA sequences as triplets of bases .
What does each triplet base encode for ?
Each triplet encodes for a specific amino acid in the protein .
How many stages does protein synthesis have ?
Protein synthesis consists of two stages .
Where does the first stage of protein synthesis take place ?
In the nucleus .
Where does the second stage of protein synthesis take place ?
In the cytoplasm .
What is the first stage of protein synthesis called ?
Transcription .
What happens in transcritpion ?
- In this stage , the base sequence of the gene is copied into a complementary template molecue .
- Scientists ca; this template RNA or mRNA for short .
- The mRna now passes out of the nucleus into the cytoplasm .
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Single stranded molecule .
What is the second stage of protein synthesis called ?
Translation .
What happens in translation ?
- In this stage , the mRNA molecule attaches to a ribosome .
- Amino acids are now brought to the ribosome on carrier molecules .
- These carrier moelcules are called transfer RNA or tRNA for short .
What happens in translation (part two )
- The ribosome now reads the triplets of bases on the mRNA and uses this to join together the correct amino acids in the correct order .
- Once the prtein chain is complete , it now folds innto the unique shape .
- The shape enables the protein to do its job .
What is a mutation ?
A mutation is a change in the genetic material of an otganism .
(Check mutation sheet )What would have happened when a single base had changed but the same sequence ?
This had no change in the amino acid sequence .
Why did the mutation not make a difference ?
- As different base triplets can sometimes encode for the same amino acid sequence .
- In this case the mutation had no effect on the protein’s shape or function . (most mutations have no effect on the protein ).
(Check mutation sheet) What has the different amino acids done ?
- They have altered the shapeof the protein .
- This has altered the shape of the protein .
-What can happen if the shape of the protein is altered ?
-Tjis caan have a dramtic effect on the protein funciton , (active site of an enxyme may change shape and no longer attach to the substrate .)
What could happen if a mutation changed the shape of a structural protein (collagen ) ?
-It may lose its strength .
Chromosomes contain coding parts of DNA and …
-Non-coding parts of DNA .
What do non-coding parts of DNA do ?
-These regions switch genes on and off - tell genes when to produce proteins .
What can mutation do to non-coding genes ?
- Mutations in these non-coding regions can affect how genes are swtiched on or off .
- A gene may be turned on when it is menant to be turned off .
What would happen if a geen is turned on when it shouldn’t be in the diagram ?
-Cell could produce a protein it isn’t meant to .
This could have a significant effect on the cell - uncontrolled mitosis - Cancer .
What is Nonsense ?
-Occurs when a substitution of a base occurs to leading to a premature ‘stop codon’ being coded for . The protein would either not form or would not function correctly .
What is Missense ?
-Occurs when a change in base leads to a different amino acid being coded for . The protein would not form or would function corrrectly .
What is Silent ?
Occurs when a substituition of a base still codes for the same aminoa cid as the original base .
If a base changes , but the codon still codes for the same amino aicd , what will happen ?
-The protein will be unchanged .
If a base changes , a different amino acid ay be used in the protien meaning …
causing the protein to be non-functional .
Soemtims a mutation will cause a beenficial change in a protein …
giving it a new function or making it more effective .
-Where do chromosomes come from ?
- One chromosome pair comes from your father .
- The other Chromosome pair comes from your mother .
What are alleles ?
Alleles are different versions of the gene
(genes come in different versions )
What is geneotype ?
The genotype of a person is the genetic makeup of an individual for a particular characteristic
What is homozygous?
-If the person has two copies of the same allele scientists say they are homozygous . (E,E)(e,e)
What is phenotype ?
The phenotpe of a person tells us the characterisics caused by the persons alleles .
On the alleles sheet , state the genotype for the three drawings , and what the phenotype is .
:))
What is heterozygous
If the person has two different alleles , this is known as heterozygous (E,e).
What is a dominant allele ? Give e.g .
- A dominat allele will show in the phenotype even if there is only one copy present .
- E.g the allele for wet ear was (E) is dominant so the persons phenotype is wet ear wax .
What is recessive allele ? Give e.g .
- A recessive allele (e) , will only show in the phenotype if two copies are present . In other words if no dominant allele is present .
- E,g (e,e)- there is no dominant allele (E) , so the phenotype is dry ear wax .
What are many characteristics a result of ? Give an example ,
Many characteristics are the result of many genes acting together , e.g height .
What is Cystic Fibrosis a disorder of ?
-Cystic Fibrosis is a disorder of cell membranes .
What is Cystic Fibrosis controlled by ?
-Cystic fibrosos is controlled by a single gene , which has two alleles .
What is the allele for normal cell membrane function?
Dominant
What is the allele for defective cell membranes ?
Recessive .
So as the allele is recessive for Cystic Fibrosis , how does offspring get Cystic Fibrosis ?
In order to have Cystic Fibrosis , the person has to have two copies of the defective allele (recessive allele ) - have to inherit a defective allele from both parents .
What is a person with one defective allelle and normal cell for Cystic Fibrosis ?
They do not have cystivc fibrosis , but are known as a CARRIER of the Cystic Fibrosis allele .
What is wrong with Punnet diagrams .
The percentages are just probabilities , so all of the offspring could be carriers , or all the offspring could be unaffected .
What happens when people have Polydactyl ?
-People with polydactyl have extra fingers or toes .
What allele causes Polydactyl ?
-Dominant alleles - meaning if a person has ONE copy of the polydactly and a NORMAL allele , they will have Polydactyl as dominant allele characteristics are always shown .
Can you be a carrier of Polydactyl ?
No - it is a dominant allele .
WHat is a solution to inherited disorders to prevent it ?
Embryo screening - in embryo screening , embryos are tested to see if they have alleles for inherited disorders .
-Embryos which do not have defective allels are implanted into the woaman . These can develop into healthy offspring .
What is one problem with embryo screening ?
-Embryos screening is expensive - some people think the money should be spent elsewhere in the Health Service .
What is the second problem with embryo screening ?
-Often a large number of embryos are created but , only a small number are implanted . This means that some healthy embryos are destroyed and some people think that is unethical .
What is the third problem with embryo screening ?
-In the future , we may be able to screen embryos to produce offspring with desirable features (e.g taller) - many find this unethical .
What is gene therapy ?
In the future , scientists may be able to correct faulty alleles and use this to treat inheried disorders - but at the moment , this is still experimental .
What do family trees show ?
Only phenotypes not genotypes .
Answer questionns on family tree video on free science lessons ?
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