Types of Mutations (أنواع الطفرات)
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- Опубликовано: 2 окт 2024
- #mutations #الطفرات #DNA_mutations
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يعني دكتور التغير اي nucleotide يجي بمكان الثاني ؟
تستاهل الفولو واللايك محاضرة شكبرها تلخصت ب٦ دقايق ممنونين منك
ياخي لو هذا الشرح لو مايراد
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هل يمكنني أن اتواصل مع حضرتك دكتور بخصوص استفسار بسيط
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حلو جداً
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هو مفيش جزء اخر لل Gene mutation ?? باقي الشرح
يعني الinsertion و deletion هم نفسهم الframshift
ممنون دكتور عاشت ايدك
ماشاء الله 💕
بارك الله بيك الله يوفقك❤️❤️❤️
عذرا دكتور اضافه نييوكلوتيدات مفروض اضافه قاعده نتيروجينه
جزاك الله خيرا
وهل تعتبر الartificial mutation هي نفسها الinduced mutation
شرح واضح وخيال شكرآ دكتور 💜
جزاك الله كل خير
هل تعتبرsilent mutation هي نفسها الpoint mutation
🙂
شرحك تمام متابعك سوداني في الزقازيق المصرية
يعطيك العافية فيديو صغير مختصر مفهوم 🎉🎉
نيوكايوتيد هل هو Amino acid or polypeptide?
قصدك نيوكليوتيد ... الوحدة البنائية لل DNA تعادل amino acid بالبروتين
قلب بباقي الفيديوهات متحدث عنهن.
Amino acids يتم ربطه مع اخوه الثاني برابط اسمها peptide
Amino acid بواسطه رابطة peptide ينم ربطه مع amino acid آخر
وعلى حسب عدد amino acid المترابطة تقدر تسمي رابطه peptide
مثلا عندنا جزئين amino acid مترابط اذا الرابطه الي بينهم اسمها dipeptide لأنهم اثنان
واذا ثلاث جزيئات بتكون بينهم tripeptide والرابعه والخمسة ... الخ
ولمن يكون عددها كثير يكون اسمها polypeptide يعني غزيرة أو متعددة الرابطه peptide .
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انا افداال العراق
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انقذتني ❤
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ممتاز
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ممكن تشرح لنا عن duplication 💔
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ممكن تعطيني رابط تحط فيه السلايدات
T.me/t91011 ابحث هنا
هل يمكن ان تصحح طفرة من تلقاء نفسها ؟
بشكل طبيعي ممكن أن يتم قتل الخلية لأن حصل بيها طفرة وهذه أحد طرق التصحيح.
سلام عليكم دكتورة وافر الشكر لحضرتك .كيف يمكن التواصل مع حضرتك
الانسجرام بوصف كل فيديو
@@MedFuture101
ممكن المعرف لحضرتك دكتور عندي مجموعة أسئلة عن الطفرات ربي يوفق حضرتك
دكتور راسلتك على التلي منذ اكثر من اسبوع
عاشت ايدك دكتور
A. Mutation
1. A mutation is a direct alteration of a gene, resulting in a new allele of that gene.
a) Changes at specific sites in a gene are called point mutations.
2. Somatic versus germinal mutations:
a) Somatic mutations are inherited only in descendants of that cell and are not transmitted to progeny. Interesting somatic mutations include naval oranges and Delicious apples; in both cases, important traits are “inherited” via vegetative propagation and grafting.
b) Germinal mutations (in diploids) are inherited directly in offspring through sexual reproduction.
3. Most mutations are deleterious and may be dominant, recessive, semi-dominant, lethal, etc.; mutation, in essence, is a random, non-adaptive process.
4. Most mutations are reversible [forward mutation and back or reverse mutation]; rates of back or reverse mutation are generally lower than rates of forward mutation.
5. Forward mutation rates range from 10-7 to 10-10 per base pair per generation; given an average “gene” (coding sequence) of 1,000 base pairs, mutations rates per gene per generation range from 10-4 to 10-7.
a) Mutation rates are “observed” rates as opposed to “actual” rates in coding, functional sequences.
6. Spontaneous versus induced mutations is a conceptual issue only, as distinguishing between spontaneous and induced mutations on a mutation by mutation basis is operationally impossible.
B. Types of mutations (at the molecular level):
1. Deletions (large or small): includes many “spontaneous” mutations, and generally includes mutations that do not revert.
2. Base substitutions: transitions and transversions
a) Classic types [samesense, missense, nonsense] from protein-coding sequences
b) Site types [intron splice junctions, promoters, enhancers, et cetera] from functional but non- coding sequences.
3. Frameshifts - historically, single base-pair insertions/deletions in the reading frame of protein- coding sequences (genes), altering the reading 'frame.'.
a) Single base-pair additions/deletions also can disrupt non-protein coding (structural genes
(e.g., tRNAs and rRNA by disrupting stem-and-loop or hairpin structures), and (but functional sites (e.g., promoters, enhancers)
4. Crosslinks - covalent links formed between bases
a) can be on the same strand (interstrand), e.g., thymine-thymine dimers
b) can be on opposite strands (interstrand)
5. Insertions - generally derived from transposons or transposable elements.
non-coding
6. Expanding trinucleotide repeats - a relatively “new” class, turning up a number of inherited neurological syndromes in humans
a) Genomes are full of short, simple tandem repeats of from two to six base pairs that generally go by the name of microsatellites or microsatellite loci.
b) When microsatellites that occur as triplets (tri-nucleotide repeats) occur in protein-coding sequences, long (often expanding) series of the same amino acid occur in the polypeptide (protein). Examples include...
(i) Up to 1,000 CGC repeats associated with fragile X syndrome (mental retardation)
(ii) CAGandCTGrepeatsassociatedwithseveralneurologicalsyndromes
c) These trinucleotide repeats are very unstable, giving rise to increasing numbers of repeats and increased severity of the associated syndrome. This phenomenon is known as anticipation.
C. Degree of expected phenotypic effect depends variously on the following.
1. Type of damage (e.g., missense versus frameshift versus insertion)
2. Site of damage (e.g., active versus non-essential sites or domains; introns versus exons, splice- site junctions versus satellite DNA sequences)
3. Dispensability (importance) of the function or of the molecule produced
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D. Mutagenesis: mutations arising from (induced by) exposure to radiation or chemicals.
1. Radiation mutagenesis: mutations that arise from ionizing (X-rays, α, β, and gamma rays) or non-ionizing (UV light) radiation.
Ionizing radiation: high energy, low wavelength
a) Mutations arise directly from structural alterations to DNA, or indirectly from structural alterations of molecules (metabolites) that interact with DNA.
b) Damage itself arises from ionization, where positively-charged free radicals result from release of electrons in target molecules.
c) Structural alterations to DNA can be severe, including disruption of covalent linkages. Damaged regions can involve nitrogenous bases, the sugar moiety, and the phosphodiester backbone.
d) Damage to DNA itself can cause a phenotypic effect, as DNA cannot be metabolized (e.g., replicated, transcribed, etc.) properly. DNA repair mechanisms can “fix” structural damage, but often do so incorrectly by removing the affected DNA but inserting an incorrect base. Note that the heritable mutation produced in such a situation actually stems from incorrect repair.
UV radiation:
a) Primary photoproducts (damage) of UV radiation are pyrimidine-pyrimidine dimers (mostly thymine-thymine dimers). Other, less frequent UV photoproducts are pyrimidine hydrates.
b) Similar to other radiation damage, DNA damaged by UV radiation must be repaired for DNA to be metabolized correctly. Again, repair can go awry and lead to a heritable mutation.
Concept of ‘error-prone’ versus ‘non-error-prone mutagenesis’
2. Chemical mutagenesis: mutations that arise from exposure to certain chemicals. Chemical mutagens are generally of two types: those that are mutagenic to both replicating and non- replicating DNA (includes alkylating agents and deaminators), and those that are mutagenic to replicating DNA only (includes base analogs & acridine compounds).
a) Alkylating agents (e.g., EMS, MMS) are chemicals that transfer methyl- or ethyl- (alkyl-) groups onto nitrogenous bases, thus altering base-pairing potential. Perhaps the most cause
of point mutations in humans is spontaneous addition of a methyl group (-CH3)
(i) EMS, for example, causes ethylation (addition of a -CH2CH3 group) at the N-7 of guanine. This causes guanine to base pair with a thymine at the next round of DNA
replication.
3
G≡C → G*=T → A=T [transition mutation]
b) Deaminators (e.g., nitrous acid, a red meat color preservative) are chemicals that deaminate (remove amine or -NH2 groups)) from nitrogenous bases.
(i) Nitrous acid (HNO2), for example, deaminates adenine to hypoxanthine. Hypoxanthine will base pair with a cytosine at the next round of DNA replication.
A=T → hypoxanthine - T → hypoxanthine = C → G≡C [transition]
c) Base analogues (e.g., 5-bromouracil) are nitrogenous bases (or derivatives) that are not normally found in DNA, but which can be incorporated mistakenly during DNA replication. Most base analogs can have base-pairing relationships that differ from the base for which they were mistaken during DNA replication.
(i) An example is 5-bromouracil, which in its normal state is mistaken for thymine during DNA replication. At a subsequent round of DNA replication, 5-bromouracil base can enter into a rare state, behave like a cytosine, and base pair with guanine, not adenine. This will lead to a G≡C base pair where there used to be an A=T base pair (transition). If 5-bromouracil shifts back to its normal state, it will base pair with adenine.
A=T → A - 5-BU → G ≡ 5-BU → G≡C [transition]
(ii) The reverse also can happen, where 5-bromouracil in its rare state can be incorporated during DNA replication in place of cytosine, shift to its normal state, and base pair with adenine at a subsequent round of replication. This will lead to A=T base pair where there used to be a G≡C base pair.
G≡C → G - 5-BU →A - 5-BU → A=T [transition]
d) Acridine compounds are molecules that bind directly (intercalate) into DNA, resulting in additions/deletions of one of a few bases. Acridines cause frameshift mutations in protein- coding sequences (genes).
e) Tautomeric shifts from enol to keto (or vice versa) forms of the nitrogenous bases, stemming from chemical (pH) fluctuations in cells, can transiently can alter base-pairing relationships.
(i) For example, such a shift can result in a rare form of cytosine that base pairs with a adenine rather than a guanine.
C≡G → C*=A → T=A [transition]
(ii) Anotherexampleiswherearareformofguaninecanbasepairwithathyminerather
than a cytosine.
G≡C → G*≡T → A=T [transition]
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