Thursday, February 3, 2011
Diversity and Evolution Animations
Posted by United JC Union at 2:14 AMHomeostasis and Cell Signalling Animations
Posted by United JC Union at 2:13 AMAnimations - Homeostasis
Animations – Cell Signalling
Biological Molecules Animation Links
Posted by United JC Union at 2:11 AM Topic: Proteins | |
No. | Web-links |
1 | |
Topic: Enzymes | |
No. | Web-links |
1 | |
2 | http://resources.emb.gov.hk/biology/english/virtual_lab/flash/enzyme_lab.html |
3 | http://www.stolaf.edu/people/giannini/flashanimat/enzymes/allosteric.swf |
4 |
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Common Mistakes & Misconceptions in Biology
Posted by United JC Union at 1:44 AM Wrong | Correct |
Ions are polar….. | Ions are charged hence they cannot pass through the hydrophobic core of the Cell Surface Membrane. |
Nucleolus contains rRNA | Nucleolus synthesizes rRNA (which forms part of ribosome), but it itself is made of DNA (coiled around histones) |
Fatty acid/ hydrocarbon tails interact with hydrophobic bonds | Fatty acid/ hydrocarbon tails interact with hydrophobic interactions |
Ribosomes have one membrane | Ribosomes do not have membranes |
Facilitated diffusion uses only channel proteins. Active transport uses only carrier proteins. | Facilitated diffusion uses both channel protein and carrier proteins. The carrier protein can change conformation without ATP hydrolysis. Active transport uses only carrier proteins which can change conformation only upon ATP hydrolysis. (Campbell 8th edition pg 135). Once, Cambridge question goes against this rule (see 2006/P2/Q1) but you still have to answer the question based on diagram. |
Passage of small, hydrophobic molecules through the phospholipid bilayer is called “diffusion” | Passage of small, hydrophobic molecules through the phospholipid bilayer is called “simple diffusion” |
Exocytosis is the same as active transport | Exocytosis is a type of bulk transport requiring vesicles, while active transport uses carrier proteins. |
Wrong | Correct |
Cellulose is a protein OR collagen is a polysaccharide | Cellulose is a polysaccharide AND collagen is a (fibrous) protein |
Collagen is made up of triple helix | Tropocollagen is made up of triple helix. |
Globular protein is globular in shape | Globular protein is spherical in shape. Use synonyms! |
Wrong | Correct |
Chromosomes are pulled to opposite ends of the cells by spindle fibres | Chromosomes are pulled to opposite poles of the cells by spindle fibres |
Centromere split | Centromere divide |
Chromosome replicate | DNA replicate (so each chromosome is now seen comprising of two sister chromatids) |
Mitosis has no homologous chromosomes | Homologous chromosomes are already in cells irregardless of whether they are undergoing cell and nuclear division. All humans have 23 pairs of homologous chromosomes. |
Diploid number = amount of DNA | Diploid number is the total number of chromosomes. DNA amount is twice in a chromosome with 2 sister chromatids compared to a chromosome that does not have sister chromatids. |
DNA replication occurs in the interphase between meiosis I and II | DNA replication occurs once only in the interphase before meiosis I |
Organism is sterile because gametes have odd number of chromosomes | Organism is sterile because the organism itself have odd number of chromosomes and/or have even number of chromosomes that do not occur in homologous pairs |
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Wrong | Correct |
Non-coding genes | Non-coding sequences/ regions Genes are already defined as coding DNA |
In leading strand, DNA is synthesized in the 5’ to 3’ direction, while in lagging strand, DNA is synthesized in the 3’ to 5’ direction | DNA polymerase III synthesizes DNA daughter strands in 5’ to 3’ direction only. Leading strand is formed due to replication towards replication fork, while the lagging strand is formed due to replication away from replication fork. |
Wrong | Correct |
Control elements are proteins/ transcription factors are DNA | Control elements (promoter, silence and enhancer) are non-coding DNA sequences. Transcription factors (which are proteins) bind to control elements to regulate transcription. |
Prokaryotes have control elements | Eukaryotes have control elements, while prokaryotes have regulatory sequences (like operator) and regulatory genes (like lacI gene). |
Bacteria divides by mitosis | Bacteria divides by binary fission. |
Wrong | Correct |
One of the electron carriers in the electron transport chain is a proton pump. | The electron carriers in the electron transport chain are coupled to proton pumps. |
Electrochemical gradient is the same as concentration gradient | Electrochemical gradient includes concentration gradient AND electric potential gradient (so be careful how you use the term!) |
When Cl- ions enter the neurone, it leads to repolarization. | When Cl- ions enter the neurone, it leads to hyperpoloarization. |
Light dependent reactions occur in the presence of light while light independent reaction occurs in the dark | Light dependent reactions occur in the presence of light while light independent reaction can occur in the presence and absence of light. |
Wrong | Correct |
The two genes are linked so closely together that crossing over does not happen. | The two genes are linked so closely together that crossing over to separate the two genes does not happen. |
Wrong | Correct |
Traits are passed on to the next generation | Genes/alleles are passed on to the next generation |
Organisms mutate to adapt to the environment | Mutations are random, they cause variation within populations |
Mutations occur at a constant rate in neutral theory | Neutral mutations have been observed/ found to occur at a constant rate in certain DNA sequences or genes |
Only silent mutation is involved in neutral theory | Neutral theory involves silent mutation and any mutation that results in a phenotype which is selectively neutral. |
Wrong | Correct |
Gene therapy is a technique for introducing healthy/ therapeutic gene | …..introducing normal allele/gene |
Package the normal allele into liposomes/ virus | Package the DNA containing the normal allele/gene into liposomes/ virus |
Deletion of a codon results in phenylalanine not to be produced/ gene lacking the amino acid | Deletion of a codon results in phenylalanine not to be coded/ protein lacking the amino acid |
Insertional inactivation can be used to distinguish recombinant plasmids from reannealed plasmids | Insertional inactivation can be used to distinguish bacteria containing recombinant plasmids from bacteria containing reannealed plasmids. |
In plant cloning, clones have same genes/ genetically similar to the same parent | In plant cloning, clones are genetically identical to the same parent |
Stem cells repair damaged cells | Stem cells replace damaged cells Stem cells repair damaged organs |
In autoradiography, expose the nitrocellulose membrane to X-ray | In autoradiography, place a piece of X-ray film over the nitrocellulose membrane, which will reveal the bands |
Southern Blotting includes gel electrophoresis | Southern Blotting is carried out AFTER gel electrophoresis. |
Independent Assortment of Chromosomes
Posted by United JC Union at 1:42 AMSynapsis
Crossing-over
Chiasmata
Bivalents
THREE Sources of Variation
Crossing Over at Prophase I
Crossing Over at Prophase I
Independent Assortment at Metaphase I
Independent Assortment at Metaphase I
Possible combinations = 2n, n = haploid number.
Humans: n = 23.
Possible combinations = 223 = 8.4 million!
Independent Assortment is also known as Mendel’s Second Law
Random Fertilization
Each Gamete
One out of about 8.4 million (223) possible chromosome combinations due to independent assortment.
2 gametes fuse
Zygote with any of about 70 trillion (223 X 223) diploid combinations!!
Mendel’s First Law
Law of Segregation
A somatic cell carries two alleles at any one locus.
Alleles of a gene pair segregate during anaphase I of meiosis
Half of the gametes carry one allele of a gene pair; the other half carry the other allele.
Summary of meiosis and mitosis
Assignment
Explain the need for the production of genetically identical cells & fine control of replication
Since the functions of mitosis are to produce new cells for growth, repair of body tissues, and asexual reproduction,
essential that the cells are identical so that the daughter cells would continue to code for essential proteins that can function properly
How to Get Seedless Watermelon?
Double the diploid number (2n) in a normal watermelon plant by the use of the chemical colchicine to tetraploid (4n).
Colchicine’s function?
Tetraploid’s gamete = 2n
Normal watermelon’s gamete = n
Fuse the tetraploid’s gamete (2n) with normal water melon’s gamete (n)
Why is triploid watermelon sterile?
During meiosis the normal pairing of chromosomes cannot properly take place since one set will have no homologous set to pair with