6 Temmuz 2015 Pazartesi
24 Mayıs 2015 Pazar
FROG’S TONGUE ‘CAN LIFT THREE TIMES OWN BODY WEIGHT’
11 MONTHS AGO BY RESISTGEZI IN ECOLOGY, ECOLOGY
“It’s not like having a liquid glue, it’s rather like a sticky tape.”Dr Thomas KleinteichUniversity of Kiel.
On average, these forces were larger than the weight of the frog itself, and in the case of one young amphibian more than three times larger. After each trial, the equipment was removed and the frog got its treat. Dr Kleinteich ultimately needed twenty measurements from each frog, so the predators had to be kept happy. Looking at the slides afterwards, the “tongue print” left behind on the glass slide offered more insights, including massive variation in the proportion of the contact area that was covered by mucus. The tongue prints left behind showed varying degrees of mucus coverage
“It’s not like having a liquid glue, it’s rather like a sticky tape.”Dr Thomas KleinteichUniversity of Kiel.
According to new research, the pulling force of a frog’s tongue can be up to three times the animal’s own weight. Zoologists placed the horned frog, a predator known to swallow whole mice, in front of a glass slide and tempted it with a tasty cricket. Stronger pulling forces were measured when contact with the glass was briefer and less mucus was left behind. The study suggests that the action of the tongue is similiar to sticky tape.
“It’s the first time we’ve ever measured how well frog tongues stick,” said Dr Thomas Kleinteich, who performed the experiments at the University of Kiel in Germany.
Dr Kleinteich works in a group that studies biological adhesives, including gecko and beetle feet, with a view to finding new designs for sticky applications like boot soles, tapes and parcel closures.
“The thing that’s interesting about frog tongues is that they’re really fast,” he told BBC News. “It only takes milliseconds.” The South American horned frog in particular, a popular pet, is known for its ability to snatch morsels up to half its own size – from locusts and fish to other amphibians and small rodents. In the wild, they lurk half-buried in wait for their prey, and then “they swallow pretty much everything that fits into their mouths,” Dr Kleinteich said.
On average, these forces were larger than the weight of the frog itself, and in the case of one young amphibian more than three times larger. After each trial, the equipment was removed and the frog got its treat. Dr Kleinteich ultimately needed twenty measurements from each frog, so the predators had to be kept happy. Looking at the slides afterwards, the “tongue print” left behind on the glass slide offered more insights, including massive variation in the proportion of the contact area that was covered by mucus. The tongue prints left behind showed varying degrees of mucus coverage
“The common belief is… that the mucus acts as some sort of superglue,” Dr Kleinteich explained. “But what we found was actually that we got higher adhesive forces in trials where we found less mucus. That was quite interesting.”
The mucus appeared to build up over time, so that cases where the tongue touched the glass for longer left more mess behind. “But during the initial contact, the mucus coverage was rather low,” said Dr Kleinteich. “So to actually establish the contact, there might be very little mucus involved.”
“It plays a role. It’s definitely a wet adhesive system, it’s not just structure and friction, because there is some fluid involved. But the key is the structure plus the mucus.
“It’s not like having a liquid glue, it’s rather like a sticky tape.”
Reference: http://www.bbc.com/
27 Nisan 2015 Pazartesi
Platypus (Ornithorhynchus anatinus)
The platypus is a semiaquatic egg-laying mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth. It is one of the few venomous mammals, the male platypus having a spur on the hind foot that delivers a venom capable of causing severe pain to humans. The fur is waterproof, and the texture is akin to that of a mole. The platypus uses its tail for storage of fat reserves. It has webbed feet and a large, rubbery snout; these features appear closer to those of a duck than to those of any known mammal. Monotremes are the only mammals known to have a sense of electroreception: they locate their prey in part by detecting electric fields generated by muscular contractions. The platypus is a carnivore: it feeds on annelid worms, insect larvae, freshwater shrimps, and freshwater yabby that it digs out of the riverbed with its snout or catches while swimming. It uses cheek-pouches to carry prey to the surface, where it is eaten.
26 Nisan 2015 Pazar
Similar but different, the fascinating mimicry
These two frogs are so similar that you might think are of the same species, but in fact they are not, they are different species, but one, Ranitomeya imitator (below), whose name could not be more appropriate, is a master of camouflage, and mimics Ranitomeya summersi (above) with remarkable accuracy.
Ranitomeya imitator, commonly referred to as Mimic Poison Frog, is known for its variety of phenotypes (morphs) even in a single population, however, at the Huallaga Canyon, R. imitator exhibits only the phenotype mimic of the sympatric and Endangered R. summersi, known from only a few localities in central Peru near the Huallaga river valley.
Photo credit: ©Brad Wilson | Locality: San Martin, Peru (2010)
Holywood Lignum Vitae - Guaiacum sanctum
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Commonly referred to as Holywood Lignum Vitae in English, and Guayacán, Guayacán Real and Palo Santo in Spanish, Guaiacum sanctum (Zygophyllales - Zygophyllaceae) is an evergreen tree that grows up to 25-30 m in height and 60 cm diameter at breast height. It has a very slow growth rate and it has been known to live for up to 1,000 years
The very attractive flowers have blue-violet petals and yellow stamens. Fruits are capsules 1.5-2.0 cm long, with four or five lobes and are bright orange-yellow when mature. They open to expose red, fleshy arils (seed coverings) which contain the hard, black, rounded seeds.
Both the timber and medicinal resin of this tree are of commercial use and have been traded for several centuries. The wood is highly sought after for its desirable qualities of strength, toughness and density. The wood is largely used as a building material.
Currently, Guaiacum sanctum is listed as Endangered species on the IUCN Red List. It is native to Mexico, Nicaragua, Puerto Rico, the Dominican Republic, the United States (Florida), Costa Rica, Guatemala, Bahamas (national tree), Haiti, Cuba, Honduras, El Salvador, Trinidad and Tobago, and the Turks & Caicos Islands. However, in some of these countries, G. sanctum has become rare or is virtually extinct.
A practical approach for assessing the melanin and blood content of the skin
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Many factors can change skin pigmentation, including aging, exposure to UV light, certain drugs, as well as certain diseases. A simple technique for measuring skin pigmentation could be a helpful tool for research and diagnostics. The same goes for measuring the skin blood content. Alteration of blood flow in the skin can, for example, be linked to skin irritations, inflammatory disorders, or diseases, such as psoriasis and rosacea. In addition, some systemic diseases, such as rheumatoid arthritis, atherosclerosis, and asthma, have shown to be associated with peripheral microvascular modifications.
Steven L. Jacques, Oregon Health & Science University, Portland, OR/USA now presents a practical approach for assessing the melanin and blood content of the skin from total diffuse reflectance spectra. It is based on the 1985 work of Kollias and Baquer who proposed using the slope of the optical density (OD) versus wavelength, OD(λ) = –log (R(λ)), between 620 nm and 720 nm as a metric for the epidermal melanin content. Jacques’ method offers a quick spectral analysis using just three wavelengths, namely 585 nm, 700 nm, and 800 nm.
More information: “Quick analysis of optical spectra to quantify epidermal melanin and papillary dermal blood content of skin,” J. Biophotonics 8:4, 309-316 (2015); doi: dx.doi.org/10.1002/jbio.201400103
25 Nisan 2015 Cumartesi
29 Mart 2015 Pazar
14 Mart 2015 Cumartesi
Evrim Ağacı neden ''dişi'' diyor?
Eşeyli üreyen canlıların (genellikle bitkiler ile hayvanların) çok büyük bir kısmı, kromozom durumuna bağlı olarak iki eşeye (cinsiyete) ayrılır: erkek ve dişi. İnsan (Homo sapiens) türünün de dahil olduğu Memeli Hayvanlar Sınıfı'nın ezici bir çoğunluğunda iki eşey kromozomu durumu görülür: XX ve XY. Bunlardan XX olanlara bilimde "dişi", XY olanlara "erkek" adı verilir.
Ne yazık ki kültürün yönlendirmelerine ve atıflarına aldanan birçok okurumuz, Evrim Ağacı olarak insan dişilerini tanımlamak için de yaygın olarak kullandığımız "dişi" sözcüğünü garipsiyor. Bu garipsemenin iki nedeni var: birincisi, bilimle uzaktan yakından alakası olmayan bir toplumsal yapıya sahip olmamız, dolayısıyla bilimsel terminolojiyi garipsememiz. İkincisi ise, insanın diğer hayvanlardan ayrı bir yeri ve konumu olduğu sanrısına ve hastalığına yaygın bir şekilde sahip olmamız. Örneğin benzer kişiler, hayvanların tekil örneklerine "birey" dediğimizde garipsiyorlar; onların "birey" olduklarına itiraz ediyorlar. İşin hukuki tanımlarını bir kenara bırakacak olursak, biyolojide her bir canlının, her bir popülasyonunun (topluluğunun, toplumunun) her tekil örneğine "birey" adı verilir. Neyse, konumuz bu değil.
İnsanların da XX kromozomuna sahip olanlarına "dişi" denir. Bu, toplumdan topluma ve zamandan zamana erkekler tarafından dişilere takılan kadın, kız, karı, avrat, hatun, dam, am, bayan, hanım, zen, zenne, nisa, nisvan, cadı, saçıuzun gibi kelimelerin aksine, halen bilimsel nötralliğini (tarafsızlığını) tamamen koruyan, hiçbir kültürel yaftayı üzerinde barındırmayan, yaygın olarak kullanılan bir sözcüktür. Dolayısıyla bir bilim sayfası olarak, herhangi bir kişi, cinsiyet, grup ve zümre tarafından dişileri çeşitli niteliklerine göre tanımlamaya ve ayırmaya çalışan bu sözcüklerden uzak bir dil yerleştirmeye çalışıyoruz. Dişi, bunun için en uygun adaydır.
Bilimde (nadiren de olsa) insanlar için yukarıda sayılan sözcüklerden "kadın" sözcüğü kullanılabilmektedir. Bu, İngilizcedeki "female" (dişi) ve "woman" (kadın) sözcükleri arasındaki ayrımdan kaynaklanmaktadır. Akademik camiada, bazı sosyal bilim araştırmaları haricinde, özellikle insan biyolojisi üzerine çalışan makalelerin çoğunda "dişi" sözcüğü tercih edilir. Biz de, eğer ki çok fazla tekrar etmemizi gerektirecek bir durum olursa, eş anlamlı bir sözcük olarak "kadın"ı tercih ediyoruz. Ancak bu gerekmiyorsa, tamamen bilimsel ve isabetli bir tercih olan "dişi"yi kullandık, kullanıyoruz ve kullanmaya devam edeceğiz.
24 Şubat 2015 Salı
23 Şubat 2015 Pazartesi
PROTEİNLER
Proteins are large molecules.
They are not really soluble, rather they form colloids
- colloids are about 500nm, which is larger than particles in solution, but smaller than particles in suspension
- colloids exist in a "sol-gel state", whereby sometimes they appear to be liquid and at other times they are jelly-like (much of the material in cytoplasm is colloid)
Proteins contain: C, H, O and N, sometimes S and P
There are an almost limitless number of proteins, which vary between species and are often species-specific (fajlagosok). They determine the characteristics of a species.
Types of Proteins
a. Structural proteins - these form the organism. eg. hair, nails, feathers, etc.
b. Physiological proteins - these carry out functions, examples include:
-enzymes (biocatalysts)
-carrier molecules (szállítómolekulák)
- pigments (eg. various colour molecules in skin and eyes, haemoglobin in red blood cells)
- hormones (chemical messengers)
- contractile material in muscles
- antibodies (disease protection)
** Proteins are rarely stored (only in seeds and eggs). Proteins are only broken down for energy if a living organism is starving.
PROTEIN STRUCTURE
- a protein is a polymer. Its monomers are called amino acids.
Image from http://api.ning.com/files/xO6ybWgUbfFlk7GUXm9d8dfR--U-fUdPOJEtDzVGgDY_/aminoacidstruc.jpg
- some amino acids are basic, others are neutral - this depends on the variable group
- some amino acids are polar and others are apolar - this depends on the variable group
-amino acids are soluble in water, where they form dipolar ions (zwitterion = ikerion), this means they have BOTH acid-base properties, so they have good buffering capacity.
Synthesis of polypeptides
- amino acids attach to each other by condensation to form covalent peptide bonds
2 amino acids condense to form a dipeptide, 3 form a tripeptide and many joined together form a polypeptide.
- if more than 100 amino acids attach together it is considered a protein
- polypeptides (and proteins) are broken down by hydrolysis
*both condensation and hydrolysis require enzymes to occur.
Structure
Primary structure: this is the number and sequence of the amino acids.
*Insulin was the first protein to have its primary structure determined by a researcher named Fred Sanger
Secondary structure: This type of structure is created by H-bonds forming between amino acid monomers
Alpha helix (eg. keratin - a major component of hair and skin)
Image from http://www.bio.miami.edu/~cmallery/150/protein/alpha-helix.jpg
Beta-pleated sheet (eg. silk protein)
Image from http://student.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/images/betasheet.jpg
-both structures can be found in a single protein.
Tertiary structure: This is the secondary structure folded in 3-dimensional space.
-usually forms globular shapes
-bonded by S-bridges (requires the amino acid cysteine), ionic bonds, H-bonds and van der Waals forces
Image from http://lectures.molgen.mpg.de/ProteinStructure/Levels/tertiary.gif
Quaternary structure: A protein has quaternary structure if it is formed of 2 or more subunits (polypeptides). They are held together by various forces including hydrophobic interactions, H-bonds and ionic bonds.
eg. Haemoglobin
Image from http://www.theironfiles.co.uk/images/Haemoglobin_Structure.jpg
Proteins can further be catagorized as simple or complex. A simple protein contains only amino acids, complex proteins often include other elements, such as the iron containing haeme molecule found in haemoglobin (above).
Protein Stability and Denaturation
A protein will be stable (maintain its shape and function) if the environment it is in is appropriate. The most common environmental factors that will cause a protein to denature (lose its shape and/or function) are temperature and pH levels. Some proteins have a wide range of tolerance (can function at 4C and at 40C), while others have a very narrow range. This is a protein-specific characteristic. An example of protein denaturation is when we cook an egg. The white of the egg is almost entirely made of the protein albumin. At room temperature it is a clear liquid. If we increase the temperature, the protein starts to denature (lose its shape and therefore function too) and it become solid and white. Denaturation occurs because the bonds between the amino acids are broken.
Sometimes denaturation is permanent (like cooking an egg), other times it can be reversible.http://bilingualbiology11a.blogspot.com.es/2010/09/lesson-4-chemistry-of-life-proteins.html
They are not really soluble, rather they form colloids
- colloids are about 500nm, which is larger than particles in solution, but smaller than particles in suspension
- colloids exist in a "sol-gel state", whereby sometimes they appear to be liquid and at other times they are jelly-like (much of the material in cytoplasm is colloid)
Proteins contain: C, H, O and N, sometimes S and P
There are an almost limitless number of proteins, which vary between species and are often species-specific (fajlagosok). They determine the characteristics of a species.
Types of Proteins
a. Structural proteins - these form the organism. eg. hair, nails, feathers, etc.
b. Physiological proteins - these carry out functions, examples include:
-enzymes (biocatalysts)
-carrier molecules (szállítómolekulák)
- pigments (eg. various colour molecules in skin and eyes, haemoglobin in red blood cells)
- hormones (chemical messengers)
- contractile material in muscles
- antibodies (disease protection)
** Proteins are rarely stored (only in seeds and eggs). Proteins are only broken down for energy if a living organism is starving.
PROTEIN STRUCTURE
- a protein is a polymer. Its monomers are called amino acids.
Image from http://api.ning.com/files/xO6ybWgUbfFlk7GUXm9d8dfR--U-fUdPOJEtDzVGgDY_/aminoacidstruc.jpg
- some amino acids are basic, others are neutral - this depends on the variable group
- some amino acids are polar and others are apolar - this depends on the variable group
-amino acids are soluble in water, where they form dipolar ions (zwitterion = ikerion), this means they have BOTH acid-base properties, so they have good buffering capacity.
Synthesis of polypeptides
- amino acids attach to each other by condensation to form covalent peptide bonds
2 amino acids condense to form a dipeptide, 3 form a tripeptide and many joined together form a polypeptide.
Formation of a dipeptide
Image from http://www.mrothery.co.uk/images/Image46.gif- if more than 100 amino acids attach together it is considered a protein
- polypeptides (and proteins) are broken down by hydrolysis
*both condensation and hydrolysis require enzymes to occur.
Structure
Primary structure: this is the number and sequence of the amino acids.
*Insulin was the first protein to have its primary structure determined by a researcher named Fred Sanger
Secondary structure: This type of structure is created by H-bonds forming between amino acid monomers
Alpha helix (eg. keratin - a major component of hair and skin)
Image from http://www.bio.miami.edu/~cmallery/150/protein/alpha-helix.jpg
Beta-pleated sheet (eg. silk protein)
Image from http://student.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/images/betasheet.jpg
-both structures can be found in a single protein.
Tertiary structure: This is the secondary structure folded in 3-dimensional space.
-usually forms globular shapes
-bonded by S-bridges (requires the amino acid cysteine), ionic bonds, H-bonds and van der Waals forces
Image from http://lectures.molgen.mpg.de/ProteinStructure/Levels/tertiary.gif
Quaternary structure: A protein has quaternary structure if it is formed of 2 or more subunits (polypeptides). They are held together by various forces including hydrophobic interactions, H-bonds and ionic bonds.
eg. Haemoglobin
Image from http://www.theironfiles.co.uk/images/Haemoglobin_Structure.jpg
Proteins can further be catagorized as simple or complex. A simple protein contains only amino acids, complex proteins often include other elements, such as the iron containing haeme molecule found in haemoglobin (above).
Protein Stability and Denaturation
A protein will be stable (maintain its shape and function) if the environment it is in is appropriate. The most common environmental factors that will cause a protein to denature (lose its shape and/or function) are temperature and pH levels. Some proteins have a wide range of tolerance (can function at 4C and at 40C), while others have a very narrow range. This is a protein-specific characteristic. An example of protein denaturation is when we cook an egg. The white of the egg is almost entirely made of the protein albumin. At room temperature it is a clear liquid. If we increase the temperature, the protein starts to denature (lose its shape and therefore function too) and it become solid and white. Denaturation occurs because the bonds between the amino acids are broken.
Sometimes denaturation is permanent (like cooking an egg), other times it can be reversible.http://bilingualbiology11a.blogspot.com.es/2010/09/lesson-4-chemistry-of-life-proteins.html
HÜCRE DÖNGÜSÜ, REPLİKASYON, MİTOZ VE MAYOZ
Topic 11: Cell cycle, DNA replication, mitosis and meiosis
DNA is found in the nucleus. It carries the genetic information in all eukaryotes.
How is DNA organized?
-its basic structure is the double helix
-this is then wound around proteins (called histones) to form chromatin. Under an electron microscope, it looks like beads on a chain. This is the form that DNA is stored in between cell divisions
-during cell division the DNA winds up more tightly and the chromatin coils on itself, looping and coiling to form thick rods called chromosomes, which are visible under the light microscope
Image from: http://themedicalbiochemistrypage.org/dna.html
What happens?
DNA is copied when it is uncondensed, then it condenses into chromosomes that have 2 halves (each a copy of the other). Each half is called a chromatid. Sister chromatids are identical. The point at which the DNA narrows and the chromatids are connected is called the centromere. Each chromosome has many genes, each gene defines a single characteristic.
The number and shape of chromosomes are species-specific. eg. Humans = 46 chromosomes, dogs = 78, pea = 14, fruit fly = 8
All sexually reproducing organisms have 2 sets of chromosomes, one from each parent (this is the diploid state). In humans a diploid cell has 46 chromosomes, half from the mother and half from the father (23). The chromosomes which carry the same kind of information are called homologous chromosomes.
Cell division
There are 2 types:
- mitosis (számtartó sejtosztodás): purpose is growth and repair, 2 identical daughter cells are produced
- meiosis (számfelező sejtosztodás): purpose is to produce gametes (sex cells) for reproduction, 4 genetically different cells are produced
The cell cycle describes the typical cycle of a somatic (body) cell that will go through mitosis:
Image from: http://www.cdli.ca/courses/biol3201/unit02/unit02_org01_ilo02/b_activity.html
During the first growth phase, the cell simply grows and carries out its normal functions. At a certain point, the cell enters the synthesis phase, where the DNA is replicated.
DNA replication refers to the creation of another DNA double helix using the first helix as a template. In order for this to occur:
Once DNA replication has occured, the nucleus then has 2 copies of all of its DNA and will continue to grow and carry out some normal functions, but it will also prepare for cell division, which is either mitosis or meiosis, depending on whether or not it is a cell that will simply copy itself, or a cell that is designed to produce gametes (eggs or sperm).
Mitosis is divided into 4 phases:
Prophase:
-chromatin condenses to chromosome
-nuclear envelope disintegrates and disappears
-spindle (magorsó) forms
Metaphase:
-chromosomes line up at the equator
Anaphase:
-chromatids are pulled to opposite poles of the cell
Telophase:
-cell plasma divides
-nuclear envelope reappears
(don't worry about the extra stages in the image below!!)
Image from: https://www.msu.edu/~robiemat/science.htm
Image from : http://imcurious.wikispaces.com/Midterm+Exam+2010+Review+P1
Meiosis occurs to produce haploid cells that will be gametes (sperm and eggs).
It is a division that reduces the chromosome number by half. It is divided into meiosis I and meiosis II
Meiosis I
Prophase I
-chromatin condenses to chromosomes
-chromosomes "find" their homologous pairs and crossing over occurs
Metaphase I
--nuclear membrane disappears
-homologous chromosomes line up at the equator and attach to spindle fibres
Anaphase I
- chromosomes pairs are split as they are pulled to opposite poles
Telophase I
- cell plasma divides
- nuclear membrane reforms
Short interphase, with no DNA replication
Meiosis II
Prophase II
-chromosomes condense
- nuclear membrane disappears
-spindle forms
Metaphase II
-chromosomes line up at the equator
Anaphase II
-chromatids are pulled to opposite poles of the cell
Telophase II
-cell plasma divides
-nuclear membrane forms
Image from: http://commons.wikimedia.org/wiki/File:Meiosis_diagram.jpg
So mitosis and meiosis share some characteristics, but are also unique in many ways. The following diagram presents a comparison of the two. Be sure to consider how they are similar and how they are different.
Image from: http://bioactive.mrkirkscience.com/09/ch9summary.html
How is DNA organized?
-its basic structure is the double helix
-this is then wound around proteins (called histones) to form chromatin. Under an electron microscope, it looks like beads on a chain. This is the form that DNA is stored in between cell divisions
-during cell division the DNA winds up more tightly and the chromatin coils on itself, looping and coiling to form thick rods called chromosomes, which are visible under the light microscope
What happens?
DNA is copied when it is uncondensed, then it condenses into chromosomes that have 2 halves (each a copy of the other). Each half is called a chromatid. Sister chromatids are identical. The point at which the DNA narrows and the chromatids are connected is called the centromere. Each chromosome has many genes, each gene defines a single characteristic.
The number and shape of chromosomes are species-specific. eg. Humans = 46 chromosomes, dogs = 78, pea = 14, fruit fly = 8
All sexually reproducing organisms have 2 sets of chromosomes, one from each parent (this is the diploid state). In humans a diploid cell has 46 chromosomes, half from the mother and half from the father (23). The chromosomes which carry the same kind of information are called homologous chromosomes.
Cell division
There are 2 types:
- mitosis (számtartó sejtosztodás): purpose is growth and repair, 2 identical daughter cells are produced
- meiosis (számfelező sejtosztodás): purpose is to produce gametes (sex cells) for reproduction, 4 genetically different cells are produced
The cell cycle describes the typical cycle of a somatic (body) cell that will go through mitosis:
During the first growth phase, the cell simply grows and carries out its normal functions. At a certain point, the cell enters the synthesis phase, where the DNA is replicated.
DNA replication refers to the creation of another DNA double helix using the first helix as a template. In order for this to occur:
1. The DNA double helix begins to unwind or unzip at one end to form a replication fork. Unwinding requires the help of an enzyme called a helicase.
2. Enzymes called DNA polymerases bind to the single strands of DNA. They then proceed to "read" the template strand (in the 5' to 3' direction) and add complementary nucleotides. Since the polymerase only travels in one direction, it will move more quickly along the leading strand, but on the lagging strand it will attach at the fork and move toward the end, until it meets up with a previously formed DNA strand fragment, then it will detach and reattach at the continuously unwinding replication fork. The fragments that are created in this way are called Okazaki fragments. They are "glued" together with the help of enzymes called ligases.
The end result is two semi-conservative daughter double helixes- meaning that each double helix contains one strand from the original and one strand that is new.
If you want to see a video: http://www.youtube.com/watch?v=teV62zrm2P0
Once DNA replication has occured, the nucleus then has 2 copies of all of its DNA and will continue to grow and carry out some normal functions, but it will also prepare for cell division, which is either mitosis or meiosis, depending on whether or not it is a cell that will simply copy itself, or a cell that is designed to produce gametes (eggs or sperm).
Mitosis is divided into 4 phases:
Prophase:
-chromatin condenses to chromosome
-nuclear envelope disintegrates and disappears
-spindle (magorsó) forms
Metaphase:
-chromosomes line up at the equator
Anaphase:
-chromatids are pulled to opposite poles of the cell
Telophase:
-cell plasma divides
-nuclear envelope reappears
(don't worry about the extra stages in the image below!!)
Image from: https://www.msu.edu/~robiemat/science.htm
Image from : http://imcurious.wikispaces.com/Midterm+Exam+2010+Review+P1
Meiosis occurs to produce haploid cells that will be gametes (sperm and eggs).
It is a division that reduces the chromosome number by half. It is divided into meiosis I and meiosis II
Meiosis I
Prophase I
-chromatin condenses to chromosomes
-chromosomes "find" their homologous pairs and crossing over occurs
Metaphase I
--nuclear membrane disappears
-homologous chromosomes line up at the equator and attach to spindle fibres
Anaphase I
- chromosomes pairs are split as they are pulled to opposite poles
Telophase I
- cell plasma divides
- nuclear membrane reforms
Short interphase, with no DNA replication
Meiosis II
Prophase II
-chromosomes condense
- nuclear membrane disappears
-spindle forms
Metaphase II
-chromosomes line up at the equator
Anaphase II
-chromatids are pulled to opposite poles of the cell
Telophase II
-cell plasma divides
-nuclear membrane forms
Image from: http://commons.wikimedia.org/wiki/File:Meiosis_diagram.jpg
So mitosis and meiosis share some characteristics, but are also unique in many ways. The following diagram presents a comparison of the two. Be sure to consider how they are similar and how they are different.
Image from: http://bioactive.mrkirkscience.com/09/ch9summary.html
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