Term
4.1.2
Define Gene, Allele, and genome. |
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Definition
Gene: a heritable factor that controls a specific characteristic.
Allele: one specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene.
Genome: the whole of the genetic information of an organism. |
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Term
4.1.3
Define gene mutation |
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Definition
Gene mutation is a random, rare change in genetic material. |
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Term
4.1.4
Explain the consequence of base substitution mutation in relation to the processes of transcription and translation, using the example of sickle-cell anemia. |
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Definition
Sickle Cell Anemia is a disorder caused by base substitution in the gene for hemoglobin. A mutation is a change in DNA swquence. A in the Gag codon on the sense strand is changed to T. GAG codon on the mRNA is changed to GUG, and Glutamic acid in the protein is changed to valine.When the mutated gene is transcribed, a codon in the mRNA will be different. Instead of normal codon GAG the mRNA will have codon GUG. This results in a mistake in translation. Sickle cell anemia is caused by 2 mutated recessive alleles. Valine has a different shape and is hydrophobic. B/c it is on the outside of the protein, the hydrophobic patch is in a watery environment. Hb mcs. stick together at the valine to hide hydrophobic part. This causes strands to form which changes the shape of the red blood cells.
Sickle cell anemia causes other health problems such as anemia and tiredness.
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Term
4.3.1
Define genotype, phenotype, dominant allele, recessive allele, codominant alleles, locus, homozygous, heterozygous, carrier and test cross.
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Definition
Genotype: the alleles of an organism
Phenotype: the characteristics of an organism.
Dominant allele: an allele that has the same effect of the phenotype whether it is present in the homozygous or heterozygous state.
Recessive allele: an allele that only has an effect on the phenotype when present in the homozygous state.
Codominant alleles: pairs of alleles that both affect the phenotype when present in a heterozygous state.
Locus: The particular position on homologous chromosomes of a gene.
Homozygous: having two of the same alleles of a gene.
Heterozygous: having two different alleles of a gene.
Carrier: an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele.
Test Cross: testing a suspected heterozygote by crossing it with a known homozygous recessive. |
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Term
4.3.3
What do some genes have? |
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Definition
More than two alleles. (Multiple alleles.) |
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Term
4.3.4
Describe ABO blood groups s an example of codominance and multiple alleles.
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Definition
-Blood types contain both codominant alleles and multiple alleles.
- A and B are codominant with each other and both dominant over O.
- Genotypes: A: Iai, IaIa. B: IbIi, IbIb, O: ii.
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Term
4.3.5
Explain how the sex chromosomes control gender by referring to the inheritance of X and Y chromosomes in humans. |
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Definition
| Sex chromosomes X and Y control gender. XX is female, XY is male. One chromosome is inherited from each parent. Mothers can only give X chromosome, Fathers can give either X or Y and this determines gender. |
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Term
4.3.6
Where are some genes present and not present? |
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Definition
| Some genes are present on the X chromosome and absent from the shorter Y chromosome in humans. |
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Term
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Definition
When the gene controlling the characteristic is located on the sex chromosome so we associate the characteristic with gender.
Females can be homozygous or heterozygous for sex-linked genes because they have 2 X chromosomes.
Males only have one of each chromosome so they only have one copy of sex-linked genes. |
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Term
4.3.8
Describe the inheritance of color blindness and hemophilia as examples of sex linkage. |
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Definition
| Both color blindness and hemophilia are produced by a recessive sex-linked allele on the X chromosome. XH is the allele for normal blood clotting and is dominant over Xh which is recessive and causes hemophilia in homozygous cases. if a mother is heterozygous she is a carrier of the disease but does not have hemophilia as the dominant allele is present. She can however pass the disease on to her offspring. Below is a punnett showing how a carrier mother and an unaffected father can pass the disease on to their offspring. |
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Term
4.3.10
Explain that female carriers are heterozygous for X-linked recessive alleles.
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Definition
| Female carriers for X-linked recessive alleles are always heterozygous since they require a dominant allele and a recessive allele to be carriers. They inherit the recessive allele from one parent and the dominate allele from the other. For example hemophilia is a sex-linked disease. If a carrier mother and an unaffected father have offspring then the unaffected father will always pass on his dominate allele to his female offspring. The carrier mother can either pass on the dominate or recessive allele. If she passes on the recessive allele to her female offspring then the female offspring will be a carrier as well. |
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Term
4.3.11
Predict the genotypic and phenotypic ratios of offspring of monohyprid crosses involving any of the above patterns of inheritance |
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Definition
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Term
4.3.12
Deduce the genotypes and phenotypes of individuals in pedigree charts.
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Definition
- Squares represent males
- Circles represent females
- Shaded symbols represent affected individuals
- Unshaded symbols represent unaffected individuals.
- If most of the males in the pedigree are affected the disorder is X-linked.
- If it is a 50/50 ratio between men and women the disorder is autosomal.
- If the disorder is dominant, one of the parents must have the disorder.
- If the disorder is recessive than neither of the parents has to have the disorder as they can be heterozygous.
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Term
3.5.1
Compare the structure of RNA and DNA
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Definition
DNA: Double strand, helix, sugar:deoxyribose, thymine.
RNA: Single strand, no helix, sugar: ribose, uracil.
Both: consist of nucleotides which contain a sugar, a base and a phosphate group. Both have bases adenine, guanine and cytosine. |
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Term
3.5.2
Outline DNA transcription in terms of the formation of an RNA strand complementary to the DNA strand by RNA polymerase. |
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Definition
| DNA transcription is the formation of an RNA strand which is complementary to the DNA strand. The first stage of transcription is the uncoiling of the DNA double helix. Then, the free RNA nucleotides start to form an RNA strand by using one of the DNA strands as a template. This is done through complementary base pairing in the 5'-3' direction, however in the RNA chain, the base thymine is replaced by uracil. RNA polymerase is the enzyme involved in the formation of the RNA strand and the uncoiling of the double helix. A terminator sequence after the gene causes RNA pol. to detach. The RNA strand then elongates and then separates from the DNA template. The DNA strands then reform a double helix. The strand of RNA formed is called messenger RNA. |
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Term
3.5.3
Describe the genetic code in terms of codons composed of triplets of bases.
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Definition
- A triplet of bases (3 bases) forms a codon.
- Each codon codes for a particular amino acid or STOP.
- Amino acids link to form proteins, DNA and RNA regulate protein synthesis.
- The genetic code is the codons within DNA and RNA, composed of triplets of bases which eventually lead to protein synthesis.
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Term
3.5.4
Translation Overview |
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Definition
- Translation is the process of protein synthesis.
- The mRNA code that came from the gene code now needs to be translated into amino acid code.
- The mRNA will attach to a ribosome in the cytoplacm & the ribosome will put the amino acids together to form the polypeptide.
- tRNA molecules will carry the amino acids to the ribosome.
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Term
3.5.4
Explain the process of translation, leading to polypeptide formation.
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Definition
Initiation- the small subunit of the ribosome binds to the 5' end of the mRNA and binds to the initiator tRNA (the one carrying MET). The anticodon attracts to the codon using H-bonds and holds the tRNA in place. The large subunit of the ribosome then attaches. Some energy(in the form of GTP) is needed for initiation. The initiator tRNA is in the P site.
Elongation-tRNA arrives in A site w/ next amino acid. The ribosome catalyzes the formation of a peptide bond between the 2 amino acids. The growing strand is now bonded to the tRNA in the A site.
Translocation- tRNA in the A site is translocated to Psite. mRNA moves with it b/c it is still H-bonded to tRNA. tRNA in P site is translocated to E site where it is released. Elongation & translocation continues until stop codon is reached.
Termination- When a stop codon is reached, a protein called release factor will bind with the stop codon in the A site. A reaction will separate the polypeptide from the tRNA in the P site. The tRNA, mRNA, ribosome subunits, and polypeptide will all separate.
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Term
3.5.5
Discuss the relationship between one gene and one peptide. |
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Definition
Originally, it was assumed that one gene would invariably code for one polypeptide but many exceptions have been discovered.
Now that we know about introns and exons, we can see that if you splice the mRNA differently, you can get several different polypeptides from one gene.
This helps explain why we have relatively few genes, only about 35,000, that code for all our proteins. About 100,000. |
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Term
7.3.1
How is transcription carried out? |
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Definition
Transcription is carried out in a 5'-3' direction.
The 5' end of the free RNA nucleotide is added to the 3' end of the RNA molecules that is already synthesized. |
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Term
7.3.2
Distinguish between the sense and antisense strands of DNA |
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Definition
- Sense strand is the gene code. Has the same base sequence as mRNA with uracil instead of thymine.
- Antisense strand is the template. Is transcribed.
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Term
7.3.3
Explain the process of transcription in prokaryotes |
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Definition
Specific sequence of DNA tells RNA pol. when to start transcription. RNA polymerase binds to the promoter region, This initiates transcription.
RNA polymerase uncoils the DNA. Only one strand is used, the template strand.
Free nucleoside triphosphates bond to their complementary bases on the template strand .
Adenine binds to uracil instead of thymine.
As the nucleoside triphosphates bind they become nucleotides and release energy by losing two phosphate groups. The mRNA is built in a 5'→3' direction.
RNA polymerase forms covalent bonds between the nucleotides and keeps moving along the DNA until it reaches the terminator.The terminator signals the RNA polymerase to stop transcription. RNA polymerase is released and mRNA separates from the DNA. The DNA rewinds. |
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Term
7.3.4
What does Eukaryotic RNA need? |
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Definition
| Eukaryotic RNA needs the removal of introns to form mature mRNA. |
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Term
7.4.1
Explain how tRNA is recognized |
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Definition
Each tRNA activating enzyme recognises a specific tRNA molecule
The tRNA molecule is made up of double stranded sections and loops
At the 3' end of the tRNA there is the nucleotide sequence CCA to which the amino acid attaches to
The different chemical properties and three dimensional structure of each tRNA allows the tRNA-activating enzymes to recognise their specific tRNA
Each tRNA enzyme binds a specific amino acid to the tRNA molecule
The tRNA-activating enzyme will bind the amino acid to the tRNA with the matching anticodon
Energy from ATP is needed during this process |
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Term
7.4.2
Outline the structure of ribosomes, including protein and RNA composition, large and small subunits, three tRNA binding sites and mRNA binding sites. |
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Definition
- Ribosomes are made up of 2 subunits, large & small
- Each subunit consists of ribosomal RNA & proteins.
- In eukaryotes, these subunits are made in the nucleoulus.
3 binding sites in the ribosome.
- The A site (aminoacyl-tRNA site) holds the tRNA carrying the next amino acid.
- The P site (peptidyl-tRNA site) holds the tRNA carrying the growing polypeptide chain.
- The E site (exit site) is the site where tRNA leaves the ribosome in search of another amino acid |
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Term
7.4.3
What does translation consist of?
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Definition
- Initiation
- Elongation
- Translocation
- Termination
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Term
7.4.4
How does Translation occur? |
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Definition
Translation occurs ina 5'-3' direction.
During translation the ribosome moves along the mRNA towards the 3' end. The start codon is nearer to the 5' end.
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Term
7.4.5
Draw and label a diagram showing the structure of a peptide bond between two amino acids. |
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Definition
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Term
7.4.6
Explain the process of translation, including ribosomes, polysomes, start codons and stop codons. |
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Definition
The tRNA containing the matching anticodon to the start codon binds to P site of the small subunit of the ribosome.The small subunit binds to the 5' end of the mRNA and moves along in a 5'→3' direction until it reaches the start codon.The large subunit then binds to the smaller one. The next tRNA with the matching anticodon to the next codon on the mRNA binds to the A site.The amino acids on the two tRNA molecules form a peptide bond.The larger subunit moves forward over the smaller one.The smaller subunit rejoins the larger one, this moves the ribosome 3 nucleotides along the mRNA and moves the first tRNA to the E site to be released.The second tRNA is now at the P site so that another tRNA with the matching anticodon to the codon on the mRNA can bind to the A site.
As this process continues, the polypeptide is elongated.Once the ribosome reaches the stop codon on the mRNA translation ends and the polypeptide is released.Many ribosomes can translate a single mRNA at the same time, these groups of ribosomes are called polysomes. |
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Term
7.4.6
What do free ribosomes synthesize?
What do bound ribosomes synthesize? |
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Definition
| Free ribosomes synthesise proteins for use primarily within the cell while bound ribosomes (attached to the ER) synthesise proteins primarily to be put in vesicles for secretion or to make proteins used in lysosomes and membranes. |
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