Author: science4all

University of Auckland B. Science degree in Biological Science University of Auckland GDip. Teaching (Secondary) course in 2009.
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Cell Division

Mitosis : Cell division in body cells (somatic cells)

When a cell is not dividing there is not much detailed structure to be seen in the nucleus. Just before cell division, a number of long, thread-like structures appear in the nucleus. These threads are called chromosomes.

Each chromosome is seen to be made up of two parallel strands, called chromatids. When the nucleus divides into two one chromatid from each chromosome goes into each daughter nucleus. The chromatids in each nucleus now become chromosomes and later they will make copies of themselves ready for the next cell division. The process of copying is called replication. It is called replication because it makes the exact copy of itself.

Mitosis has specific function in producing new cells for growth or replacement.

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Meiosis: Cell division in sex cells(sperm/egg) of reproductive organs.

In a cell which is going to divide and produce gametes, the diploid number of chromosomes shorten and thicken as in mitosis. The pairs of homologous chromosomes, lie alongside each other and when the nucleus divides for the first time. It is the chromosomes and not the chromatids which are separated. This results in only half the total number of chromosomes going to each daughter cell.

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(연습) LV3 NCEA Q: DNA Replication

DNA REPLICATION

NCEA Type Questions

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Part A:

1. Describe the function of DNA polymerase.

2. Describe the significance that the 3′ and 5′ ends have in the process.

3. Discuss the ways in which complementary strands are formed.

4. Explain why the process is necessary for the growth of living organisms.

–> Model Answer to this question

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Part B: DNA is made up of two polynucleotide chains.

1. What group of biochemical compounds are composed of nucleotides?

2. What component molecules make up a nucleotide?

3. Where in a human cell does replication of DNA occur?

4. Draw and show what is meant by semi-conservative replication.

5. What percentage of DNA in the second generation cell would have come from the parent cell?

–> Model Answer to this question

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Part C:

1. Describe the process of DNA replication.

2. DNA replication is described as a semi-conservative process. Explain what is meant by semi-conservative.

–> Model Answer to this question

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*Try to practice writing essay type questions. NCEA external examination questions will be asking you to ‘Discuss’ or ‘Explain’ about a topic.

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Food web

This is a diagram of a food web. Almost all animals must eat other organisms to obtain energy. Animals do not generally eat just one thing, nor are they eaten by only one thing. This means that each organism, through feeding, is interconnected to many different organisms. A food web shows how all species in a community are connected.

Let’s think about the organisms in an environment. If any one species is disturbed, then all species will undergo changes in its population. Eg. If small fish numbers go down then snail and cockle numbers will go up. Big fish and seabird numbers will go down.

An animal can be both a predator and a prey. For example, a small fish may eat certain types of snails, but he may also be eaten by a duck. So the small fish is both predator and prey in this food web..

Almost all animals must eat other organisms to obtain energy. Animals do not generally eat just one thing, nor are they eaten by only one thing. This means that each organism, through feeding, is interconnected to many different organisms. A food web shows how all species in a community are connected.

We, humans, often upset the balance of different populations in natural ecosystems, or change the environment so that some species find it difficult to survive. We reduce the amount of land available for animals and plants by: building; quarrying; farming; dumping waste.

Our activities may pollute: water ‐ with sewage, fertiliser or toxic chemicals; air ‐ with smoke and gases such as sulfur dioxide; land ‐ with toxic chemicals, such as pesticides and herbicides, which may be washed from land into water.

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What’s for dinner?

Ecology is the study of organisms and their relationship with their surroundings. Ecologists study the interaction between an organism and its environment. Some ecologists study a specific species or habitat. They might study the behaviour of a single species to see how it interacts with other organisms and the environment. Or, an ecologist might study many different species that either depend on each other (a food web, for example), or compete with each other for food and space

Every organism needs to obtain energy in order to live. For example,plants get , energy from the sun, some animals eat plants, and some animals eat other animals.

A food chain is the sequence of who eats whom in a biological community (an ecosystem) to obtain nutrition.

  • The arrows indicate the direction of energy flow.
  • The food chain moves food from one organism to another, giving energy to the organism digesting the food.

Eg. Buttercup → Bee → Thrush → Hawk. Plankton → Herrings → Salmon →Seals → Killer whales

  • All food chains start with the sun which provides energy for plants.
  • Photosynthesis by plants converts light energy to food. Plants are considered producers because they make their own food.
  • The producers above are grass, buttercup, rosebush and plankton.
  • Animals, including humans, cannot make their own food. As a result, they must get their energy from other sources, usually plants and other animals. Thus, animals are considered consumers.

As you can see in the diagram, food chain is the sequence of who eats whom in a biological community (an ecosystem) to obtain nutrition. Every organism needs to obtain energy in order to live. For example, plants get energy from the sun, some animals eat plants, and some animals eat other animals.

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DNA란….!

Chromosome(염색체):  http://www.tiricosuave.com/images/chromosome.jpg

Structure of DNA: http://www.scq.ubc.ca/wp-content/dna.gif

모든 세포는 핵(nucleus)를 가지고 있는데 이 안에 들어있는것이 Chromosome이다. 앞서 설명했던 것과 같이 chromosome은 DNA로 이루어져있다. DNA는 두개의 긴 테이프가 사다리로 연경되어 나선형으로 돌고있는 형태를 취하고 있으며, 세포가 활성을 유지하기 위해 필요한 모든 정보를 지니고 있다.

만일, DNA에 구조상 결함이 있거나 DNA의 양이 충분하지 못할경우 세포의 기능은 물론 분열(Cell Division: Mitosis, Meiosis 참고)에 지장을 초래한다. 이 이유는, 세포가 분열할때 DNA는 본래의 DNA와 똑같은 두개의 DNA를 복제하는데, 이 복제가 무슨 이유에서든 일어날 수 없으면 그 세포는 두개의 세포로 나누어 질수 없거나 chromosome의 갯수(number)가 부족하게 된다.

Chromosome의 number가 달라질경우 이 세포는 죽음으로 이루게 되거나, 잘못된 세포로 임신을 하게되면 기형아기가 태어난다.

Deoxyribonucleic acid (DNA)

  • Nucleic acid (there are two nucleic acid found in living organisms, which is RNA and DNA)
  • Contains the genetic instructions used in the development and functioning of all known living organisms
  • Storage of information
  • DNA is like blueprints or a recipe, or a code,
  • It contains the instructions needed to construct other components of cells (eg. proteins)
  • DNA segments that carry this genetic information are called genes
  • Involved in regulating the use of this genetic information.

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Cancer

불치의 병으로 여겨졌던 질병이었지만 이제 암의 완치율이 증가하고 있는 이유는 조기발결을 위한 검진, 수술의 개선, 방사선요법의 출현과 약물요법의 발달이라고 볼수있다. 암에 대해서 많이 들어보기도 했고 암환자들의 이야기도 방송에 자주 출연하지만 과학과목을 듣는 학생들 조차도 암이 어떤 질병이고 어떻게 발생하는지 잘 모르고 있다.

오늘은 ‘암'(Cancer) 에대해서 설명할텐데 전문용어가 많이 나오기때문에 한국어와 함께 영어를 써야할것 같다. :) 모르는 단어는 물어보시길…

인체의 구성단위는 세포(cell)이다. 인체의 성장은 세포의 분열(cell division)으로 이루어진다. 세포의 분열은 성인이 될때까지 지속되는데, 성인이 되더라도 모발(hair), 피부(skin), 위장관의 상피(villi), 생식기관(reproductive organ), 골수(bone marrow)등 신진대사(metabolism)가 활발한 기관에서는 여전히 왕성한 게포분열을 보인다.

각 장기(organ)를 이루고 있는 세포군(tissue)은 장기의 이익을 도모하려는 합목적적인 기능을 발휘하며, 필요이상의 세포분열은 정상적으로라면 제어되야한다.

미성숙한 세포(pre-mature)는 분열에 따라 자신이 소속된 장기의 특이한 고유기능을 가지게되면서 성숙(mature)해진다. 세포가 성숙해지는 시기가 오면 세포의 분열이 멈추게 된다. 예를들자면 자극전달의 기능을 가진 신경세포나 운동을 담당하는 근육세포는 영구히(permanently) 분열이 정지된다. 산소운반의 기능을가진 적혈구도 일단 골수(bone marrow)에서 성숙해지면 분열할수가 없다. 간세포의 경우는 조금 다른데, 정상시에는 분열하지 않다가 손상을 입게되면 (damage) 매우 왕성하게 분열한다.

암은 한개 또는 여러개의 비정상적인 세포로 부터 발생하며, 비 정상적인 세포분열을 제어하는 조정으로부터 벗어나 자동적으로 분열을 계속하는 특징을 가졌고 미성숙한 세포와 유사한 분열을 고수한다.

이때문에, 자신이 소속한 장기에서 이탈하여 다른 장기로 전이하고 정착하면서 상당한 크기로 분열하게 되면 장기전체를 파멸로 이끌게된다. 예를들면 장(intestine)에있는 세포가 허파(lung)으로 옮겨가 허파의 tissue사이에 장세포가 이전되 허파기관을 망가트려 놓는 것이다.

암을 쉽게 발견하지 못하는 이유는, 암중에는 분열 및 성장이 매우 더딘 종류가있어 수년내지 십수년간 전혀 증상을 초래하지 않는 경우도 있다. 그중에 하나가 전립선암(Prostate cancer)이다. 그러나 대부분 정상조직보다 분열이 빠르며, 이거슬 저지할수 있는 면역기전(Immune system)이나 방어기전(Defensive system) 이 무너지면 급속히 자라기 시작한다. 어떤암들은 두배로 성장하는 시간이 하루종도 밖에 안된다.

암의 중요한 특징을 몇가지 들수 있는데, 첫째로 정상조직보다 빨리 자라서 딱딱한 종괴로 발견되며, 둘째로 암조직과 정상조직과의 경계가 불분명하고, 세째로 원방부위에서 타부위로 전이되는 성향이 있다.

일반적으로는 성장속도가 느린 암일수록 크게 자라지 않는 한, 전이가 드물고, 성장속도가 빠른 암일수록 조기에 전이가 가능하다.

전이되는 대표적인 경로는 혈액을 통하여 간,폐,골(brain)등으로 가거나 임파관(Lymph vessels)를 통하여 임파선으로 갈수 있고, 인접 장기에 직접 침윤해 갈 수도 있다.

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Light and Reflection

What is light???

Light is a type of energy which travels as a wave from a luminous source (eg the Sun, a flame, or a torch). Not everything is a light source. Paper reflects light from a light source towards your eyes, making you able to see it.

Light travels at a speed of 3×108 m/s. Light travels faster than sound which is why you see a flash of lightning before you hear thunder! It takes 8 minutes for light from the Sun to reach Earth.

Light travels in straight lines. It can’t bend itself around objects if they are in its path. Shadows occur where light has been blocked by an object.

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Light reflection

Lots of spectacular and beautiful effects are caused by the reflection of light. Reflections occur when light bounces off the surface of water or some other smooth surface into your eyes.

Reflection from smooth surfaces (eg mirrors or calm water) leads to regular reflection. Bumpy or rough surfaces do not reflect light evenly. The light isscattered in all directions, and usually we cannot see an image. This is known as diffuse reflection.

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Mirror: Light reflection

Light can be made to change direction with mirrors – this is called reflection. When light is reflected off a mirror, the angle at which it hits the mirror (angle of incidence) is the same as the angle at which it is reflected off the mirror (angle of reflection). The rays of light which hit the mirror are called the incident rays; those reflected off the mirror are called the reflected rays. The angles are always measured from the ray to the “normal”. The normal is a line at right angles to the mirror.

The laws of reflection Terms:

  • Angle of incidence: The angle between the ray of light that hits the mirror and the normal.
  • Angle of reflection: The angle between the ray of light that is reflected off the mirror and the normal.
  • Incident ray: The ray shinning onto the mirror.
  • Reflected ray: The ray that bounces off the mirror. Normal: A line that is drawn at right angle(90°) to the mirror

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Light reflected from a plane mirror

If the angle of incidence and the angle of reflection are measured using a protractor then we will always find that

ANGLE OF INCIDENCE = ANGLE OF REFLECTION

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Curved mirrors: Images

  • Images in convex mirrors are always smaller & the right way up.
  • Uses of convex mirrors: shop-lifting mirror, mirror at a road corner.
  • Images in concave mirrors can be: larger and the right way up, if eye is very close to the mirror OR smaller and upside down if eye is away from mirror.
  • Uses of concave mirrors: shaving mirror, dentist mirror.
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Reaction and Enzyme

  • Cells are able to build up and break down their proteins, lipids and carbohydrates or change one to the other.
  • Eg. Animals cells build up glycogen from glucose.
  • all cells can make proteins from amino acids and they can build up fats from glycerol and fatty acids.
  • Animals cannot make proteins unless they are supplied with amino acids.
  • Plants can make their own amino acids starting from sugar and salts.

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Lock and key model

http://www.scienceclarified.com/images/uesc_05_img0235.jpg

세포안에서는 수많은 물질들이 합쳐졌다가도 분해되기도 한다. 이런 chemical reactions의 속도를 맞추어주는것이 enzyme의 기능이다. Enzyme이 작용하기 위해서는 알맞는 온도와 pH가 맞아야만 하고, active site(접착기면)에 substrate(기질)이 정확이 맞아야만 한다.

Substrate가 자기만의 모양을 가지고 있듯이 화학 반응이 일어나는 표면인 active site또한 자신만의 모양을 가지고있다. 퍼즐과 퍼즐이 맞아떨어저야 그림을 이루듯, 이 두가지가 정확이 맞아떨어질때 반응이 일어나는것이다.

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Enzymes are proteins that act as biological catalysts.

  • made in the cells
  • catalyst is a chemical substance that speeds up a reaction but does not get used up during the reaction.
  • anabolic enzyme reaction = join two other molecules together and form a more complicated substance. Large molecules are built up from smaller molecules.
  • Catabolic enzyme reaction = split large molecules into smaller ones.

Enzymes을 공부할땐 5가지를 꼭 기억해서 외우자.

1. Enzymes and temperature:

A rise in temperature increases the rate of most chemical reactions. A fall in temperature slows down. However, if the temperature is too high for the enzyme (eg. above 50’C) protein can be denatured and stop working. The shape of an enzyme molecule is very important if it has to fit the substances on which it acts.

2. Enzymes and pH:

Acid and alkaline conditions alter the chemical properties of enzyme. Most enzymes work best at particular level of acidity or akalinity (pH).

3. Enzymes are specific for substrates:

Enzyme that normally acts on one substance will not act on a different one.

4. Rates of enzyme reaction:

  • depends on the temperature and pH
  • concentration of the enzyme and its substrate

5. Intra- and extracellular enzymes: All enzymes are made inside cells. Most of them remain inside the cell to speed up reactions in the cytoplasm and nucleus.

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Macromolecules of living cells

Cell physiology란 세포가 정상적으로 작용하기 위해 작동하는 물리적인 활동을 말한다. 소화작용, 혈액순환 뿐만 아니라 근육축소운동까지도 포함된다. 이런 다양한 물리적인 활동을 위해 우리몸은 각각 다른세포가 다른 기능을 하기위해 모양까지도 정교하게 디자인 되어있다.

The chemical components of a cell:

1. water:

  • Good solvent
  • chemical reaction
  • water pressure in vacuoles(plant) keeps the cell turgid
  • high thermal capacity – it can absorb a lot of heat without its temperature rising to levels which damage the proteins in the protoplasm. (물은 섭씨 100도나 되어야 끓을수 있는 물질이다. 그런 성질때문에 더운 날씨에도 잘 끓지않기때문에 단백질이 잘 상하지 않게된다. 하지만 0도에서 얼기때문에 영하로 내려가는 날씨에는 동상에 걸리거나, 식물들이 얼어죽게 된다.)

2. Protein: Polymers

When small organic molecules (monomers) are joined together – huge macromolecules (polymers) are formed when small organic molecules (monomers) are joined together – huge macromolecules (polymers) are formed.

  • Carbohydrates consist of monosaccharide
  • lipids consist of fatty acids
  • proteins consist of amino acids
  • nucleic acids consist of  nucleotides
  • protein has C,H,N,O,S in its molecule
  • most abundant macromolecule in the cell
  • structural, transport, hormonal functions
  • proteins very diverse in living organisms
  • 20 dif. amino acids in all living things
  • amino acids are linked together by a peptide bond
  • Enzymes accelerate chemical reactions in cells. Enzyme은 자신은 소모되지 않고 세포안의 화학작용이 빨리 진행되게 도와주는 단백질이다. 하지만 높은 온도나, 맞지 않는 pH에서는 denature가 되어버린다.
  • Denaturation = Shape of the molecules alter, and proteins loose its original properties. Proteins form enzymes and many of the structures in the cell, so if they are denatured the enzymes and the cell structures will stop working and the cell will die.

3. Carbohydrates

  • Simple, soluble sugars or complex materials like starch and cellulose.
  • all carbohydrates contain carbon, hydrogen and oxygen only
  • commonly occurring simple sugar is glucose
  • Monosaccharides = single carbon ring
  • Disaccharides = two carbon rings in their molecules
  • Polysaccharides = many glucose molecules are joined together, the carbohydrates. Not readily  soluble in water. eg) glycogen, starch, cellulose

4. Salts (ions)

  • salts are present in cells in the form of their ions eg. sodium ions, chloride ions
  • ions take part in and influence many chemical reactions in the cell.
  • involved in determining how much water enters or leaves the cell.
  • calcium, potassium, and sodium ions are particularly important in chemical changes related to electrical activities of a cell.
  • Important for responding to stimuli or conducting nerve impulses.
  • a shortage or excess of ions in the cells upsets their physiology and affects the normal functioning of the whole organism.

5. Vitamins

  • plants can make their own vitamins
  • animal cells have to be supplied with vitamins ready made.
  • play a part in chemical reactions in the cell
  • eg. transfer energy from one compound to another
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I will be away – NOT ANY MORE!!

Hey, I was planning for the camp – but not anymore… so sad to miss out on this one because I always have enjoyed and made lots friends every year. T_T

However, I have life and job issues in 2010. If you are looking for an awesome summer break, let me know! Because they need you!!!

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From (Tues) 5/Jan/2010 to (Tues) 12/Jan/2010

I will be  leading a group for Ponui Junior Camp (Year9-10), at Ponui Island.  There will be 68 kids and a leadership team of 31.

What is Ponui Junior Camp? Here is bit about the camp.

Ponui Island in the hot afternoon sun – waterslide, kayak, sail, fish. Amped teenagers playing sport and crazy water games. Ponui at night … cook-outs, the call of kiwis. Can you see it? Can you feel it? Get there! Ponui 2010

For more info, visit – http://www.scriptureunion.org.nz/camps/ponuijunior.htm