DSE 生物BIOLOGY 區

thank you very much!
其實我都覺呢課好多都係common sense黎

睇表達乜野
想show埋material cycling 就會有埋decomposers

巴打 咁可以點溫E1E4？
上年拎4買咗卷差幾分拎5
今年想星但E14無從入手
mc23／36 pp2 14／40 累事
以前本身喺學校paper1拎開七成幾

MC 23/36 都同5爭左一截
E1 concept容易 失分大多數係冇用marking key word 答題
例如heart pumps faster and stronger
Intercostal muscle contracts stronger and quicker which causes breathing deeper and faster
A larger proportion of water is reabsorbed之類
仲有温熟堆oestrogen progesterone FSH LH

E4 明左primer design 同selection基本上冇難嘅野
係要背埋個堆bioethics

因為chromosome頭尾係一個叫telomere既野 佢係限制一粒cell可以最多divide幾多次/DNA replication既次數

攞去cloning粒somatic cell nucleus多數係由adult animal去攞 所以果d chromosomes會有shortened telomere 所以相比正常somatic cell唔可以divide太多次 所以clone會短命d

mc喺學校拎開30-32
利申band1英中
係我考嗰陣太自以爲是裸考咗先搞成咁

btw唔該巴打

5點解唔係carbohydrate

By marking scheme, item no. 5
第一屆開始就已經係咁
Phy好多人咁樣屈分
Bio就少數會E1E2E4咁做

覆左我
的確係計最高分

呢條考common sense，冇得讀書讀返黎，當年好多人錯。
你睇返2015 Marking啦

想問如果考fingerprinting係咪知佢係a technique to identify individuals by analysing the length of variable regions of DNA among different individuals
variable regions使唔使知埋係咩short tandem repeats, vntrs 同佢definitions
重有咩rflp restriction fragment length polymorphism
同埋gel electrophoresis 最後個step 知係stain or copying them to a photographic film就得
唔使理咩nylon Membrane, DNA hybridisation 個d 可
唔好意思，理解唔到個elective 要讀到幾細，巴打如果可以，可唔可以講下

再睇多次應該都要温，唔係好明rflp 同pcr-StR 有咩分別？ 我知後者用Pcr， 前者唔用，前者用DNA Hybridisation ,後者唔用，但唔明點解，同埋幾時用Pcr-str 幾時用rflp ，thanks巴打

兩者都係做dna fingerprinting 但係PCR-STR會準d

直接用STR就咁一攞DNA sample就有 好方便 但係RFLP要攞完sample再用restriction enzyme去digest

所以依家做親子鑑定法證果d都係用PCR-STR

PCR其實只不過係一種方法去amplify你想要既DNA 因為正常你攞d DNA sample會得好少唔夠做實驗
PCR完你先夠多DNA 之後你都可以用黎做RFLP


假設你想做RFLP:
DNA sample, PCR, restriction enzyme digestion, gel electrophoresis睇band

假設你想做PCR-STR:
DNA sample, PCR, gel electrophoresis睇band


你講果個DNA hybridization其實係用黎做其他野 唔關事

RFLP你可以當好似下面咁
Person 1: XXXXXAXXXXXXXXXXBXXXXXXX
Perosn 2: XAXXXBXXXXXXXXXXXXXXXXXX
A: Restriction enzyme site A
B: Restriction enzyme site B
X: DNA Sequence
因為人既DNA有tandem repeats之類既variable junk sequence所以A同B兩個SITE之間既DNA length人與人之間會有差別
當你用RE A同RE B去分別Digest呢兩個人既DNA就會出現
Person 1:
XXXXXA
XXXXXXXXXXB
XXXXXXX
Person 2:
XA
XXXB
XXXXXXXXXXXXXXXXXX
兩組唔同既DNA fragments, 而RFLP就係用呢堆fragment做一個人既signature

而PCR-STR就係直接用PCR去amplify個堆tandem repeats
因為係tandem repeat前後應該每個人都有share既common sequence
所以你只需要design對primer flank個tandem repeat就可以amplify成個tandem repeat motif出黎
例如:
Person 1: XXXXXPXXXXXXXXXXPXXXXXXX
Perosn 2: XPXXXPXXXXXXXXXXXXXXXXXX
P = primers
Person 1 出現既fragment: XXXXXXXXXX
Person 2出現既fragment: XXX

VNTR同STR只係講緊個tandem repeat既長度, 兩樣野性質相同

RFLP要做nylon membrane transfer同hybridization (probing)唔係你所講唔關事
係因為RFLP係可以用genomic DNA做
如果你用gDNA CUT完之後出現既只會係一個smear 根本唔會見到有band
probe佢係為左令某幾條band出現

巴打，咁點解pcr-str 唔使DNA hybridization同唔使Radioactive Probe ,佢就咁就睇到band?

Thanks 兩位巴打先

DNA 係肉眼睇唔到
所以做gel electrophoresis 係要做dna staining
DNA staining可以用fluorescent dye或EB stain
但係因為RFLP上面太多DNA，所以如果你直接gel stain只會出現一pat野

即係Pcr-str可以用dna staining ，因為DNA amount 唔多，所以唔使用hybridization ,我咁講啱唔啱