ENGLISH FOR BIOLOGY ENGLISH FOR BIOLOGY Ho Chi Minh City University of Industry - HUI Institute of Biotechnology and Food Technology Assessment:  Credit point: 2  Assessed as: Graded  Note: There is compulsory school attendance. Page 1 ENGLISH FOR BIOLOGY UNIT 1: CELLS AND TISSUES GROUP 1 THE CELL Almost everything in the world is made up of smaller things. Houses are built out of individual bricks and pieces of wood. Cars are built out of pieces of metal, plastic, and rubber. Think about your cell. What parts make up your cell? The Cell Theory One very important similarity among all living things is that they are made of cells, the smallest units of life. In 1838, two biologists, Schleiden and Schwann, studied many cells and made some conclusions. From their observations they developed what is known as the Cell Theory. Since then, this theory has been central to our understanding of biology. This theory states that: 1. All life forms are made from one or more cells. Some organisms, like bacteria or paramecium, are only one cell big. These are called unicellular organisms (uni-=one). Other organisms are multicellular: that means they are made up of more than one cell (multi-=more than one). For example, the human body consists of billions of cells! 2. Cells only arise from pre-existing cells. A cell can make copies of everything it has inside it, then divide itself in two, making two new cells. This process is called mitosis, or cell division. In this way, organisms can keep growing or replace damaged or old cells. For example, the formation of new cells is what allows your body to grow, or what replaces your damaged skin when you fall and skin your knee, making you good as new! 3. The cell is the smallest form of life. There is nothing smaller that is alive, and life requires what is inside a cell. For example, the molecules that make up the parts of the cell, such as sugars, fats and proteins are not alive. The separate regions of the cell are not alive on their own. Life can only be reduced down to the cellular level-thus cells are the smallest unit of life! Page 2 ENGLISH FOR BIOLOGY The Cell and Its Organelles Even the cell is made up of smaller parts. These parts are called organelles (little organs). They divide up all the work that the cell has to do. In the human body, we have different organs to do different jobs that help us live: for example, our lunges help us breathe while our brain helps us think. It’s the same in a cell: the different organelles have different jobs, and together they help the cell live. In a unicellular organism, one cell does all the jobs the being needs to survive, and the cell divides up these jobs among its organelles. In multicellular organisms, many cells come together to make a living being. Just like in unicellular organisms, the cells of a multicellular organism have organelles which divide up the cell’s work 1. Nucleus. The nucleus is the control center of the cell. It houses all the genetic information, DNA in the form of chromatin, that tells the cell what to do. DNA is like the recipe for the cell: all the instructions are there, and the organelles of the cell help to read it and build the final products: proteins! When the cell reads its DNA recipe in its nucleus, it converts these instructions to another form called messenger RNA (mRNA), which is like translating from one language to another in a process called transcription. 2. Endoplasmic reticulum (ER). The ER is like a little maze of tubes that are hollow inside. Add a few cake sprinkles right next to the ER. These are ribosomes. After mRNA is made in the nucleus, it is sent to the ribosomes on the ER. The ribosomes are responsible for reading the mRNA message and making the proper protein according to its instructions. This process is called translation. As a protein is made, or “translated,” the ribosomes pushes it into the maze of the ER. A second type of ER, called the smooth ER is where fats are formed. It is called smooth ER because it has no ribosomes on it. Page 3 ENGLISH FOR BIOLOGY 3. The Golgi body. The proteins made by the ribosomes that are inside the ER are sent to the Golgi for finishing touches and distribution. Here, the protein may be packaged or changed: it’s like putting the paint on a car being made in a factory before it is sent out to the car dealer! 4. Mitochondria are often referred to as the powerhouses of the cell, for it is within them that energy is released from organic molecules by the process of Cellular respiration. This energy is needed to keep the individual cells and the plant functioning as a whole. Carbon skeletons and fatty acid chains are also rearranged within mitochondria, allowing for the building of a wide variety of organic molecules. Mitochondria are numerous and tiny, typically measuring from 1 to 3 or more micrometers in length and having a width of roughly one half micrometer; they are barely visible with light microscopes. They appear to be in constant motion in living cells and tend to accumulate in groups where energy is needed. 5. To the lysosome, which is full of molecules that can break down cellular waste. Lysosomes are the garbage dumps of the cell—they break down waste and dispose of it properly. Lysosomes are relatively large vesicles formed by the Golgi. They contain hydrolytic enzymes that could destroy the cell. 6. How does the cell stay together? They are housed in a double-layered coating called the plasma membrane that gives the cell its shape. This membrane helps control what goes in and out of the cell, and Page 4 ENGLISH FOR BIOLOGY helps protect the cell from damaging things in the environment. The cell membrane functions as a semi- permeable barrier, allowing a very few molecules across it while fencing the majority of organically produced chemicals inside the cell. Electron microscopic examinations of cell membranes have led to the development of the lipid bilayer model (also referred to as the fluid-mosaic model). The most common molecule in the model is the phospholipid, which has a polar (hydrophilic) head and two nonpolar (hydrophobic) tails. These phospholipids are aligned tail to tail so the nonpolar areas form a hydrophobic region between the hydrophilic heads on the inner and outer surfaces of the membrane. 7. Ribosomes are the sites of protein synthesis. They are not membrane-bound and thus occur in both prokaryotes and eukaryotes. Eukaryotic ribosomes are slightly larger than prokaryotic ones. Structurally the ribosome consists of a small and larger subunit. Biochemically the ribosome consists of ribosomal RNA (rRNA) and some 50 structural proteins. Often ribosomes cluster on the endoplasmic reticulum, in which case they resemble a series of factories adjoining a railroad line Page 5 ENGLISH FOR BIOLOGY UNIT 2: DNA STRUCTURE GROUP 2: INTRODUCTION Our genes are made of deoxyribonucleic acid (DNA). This remarkable molecule contains all the information necessary to make a cell, and DNA is able to pass on this information when a cell divides. This chapter describes the structure and properties of DNA molecules, the way in which our DNA is packaged into chromosomes, and how the information stored within DNA is retrieved via the genetic code. THE STRUCTURE OF DNA Deoxyribonucleic acid is an extremely long polymer made from units called deoxyribonucleotides, which are often simply called nucleotides. Figure 4.1 shows one deoxyribonucleotide, deoxyadenosine triphosphate. Note that deoxyribose, unlike ribose, has no OH group on its 2’carbon. Four bases are found in DNA; they are the two purines adenine (A) and guanine (G) and the two pyrimidines cytosine (C) and thymine (T) (Fig. 4.2). The combined base and sugar is known as a nucleoside to distinguish it from the phosphorylated form, which is called a nucleotide. Four different nucleotides join to make DNA. They are 2’-deoxyadenosine-5’- triphosphate (dATP), 2’-deoxyguanosine-5’-triphosphate (dGTP), 2’-deoxycytidine-5’-triphosphate (dCTP), and 2’-deoxythymidine-5’-triphosphate (dTTP). DNA molecules are very large. The single chromosome of the bacterium Escherichia coli is made up of two strands of DNA that are hydrogen-bonded together to form a single circular molecule comprising 9 million nucleotides. Humans have 46 DNA molecules in each cell, each forming one chromosome. We inherit 23 chromosomes from each parent. Each set of 23 chromosomes encodes a complete copy of our genome and is made up of 6 × 10 9 nucleotides (or 3 × 10 9 base pairs—see below). We do not yet know the exact number of genes that encode messenger RNA and therefore proteins in the human genome. The current estimate is in the range of 30,000. Table 4.1 compares the number of predicted messenger RNA genes in the genomes of different organisms. In each organism, there are also approximately 100 genes that code for ribosomal RNAs and transfer RNAs. Page 6 ENGLISH FOR BIOLOGY . Figure 4.3 illustrates the structure of the DNA chain. As nucleotides are added to the chain by the enzyme DNA polymerase, they lose two phosphate groups. The last (the α phosphate) remains and forms a phosphodiester link between successive deoxyribose residues. The bond forms between the hydroxyl group on the 3’carbon of the deoxyribose of one nucleotide and the α-phosphate group attached to the 5’ carbon of the next nucleotide. Adjacent nucleotides are hence joined by a 3’–5’phosphodiester link. The linkage gives rise to the sugar–phosphate backbone of a DNA molecule. A DNA chain has polarity because its two ends are different. In the first nucleotide in the chain, the 5’ carbon of the deoxyribose is phosphorylated but otherwise free. This is called the 5’ end of the DNA chain. At the other end is a deoxyribose with a free hydroxyl group on its 3’carbon. This is called the 3’end. Page 7 ENGLISH FOR BIOLOGY The DNA Molecule Is a Double Helix In 1953 Rosalind Franklin used X-ray diffraction to show that DNA was a helical polymer. James Watson and Francis Crick demonstrated, by building three dimensional models, that the molecule is a double helix (Fig. 4.4). Two hydrophilic sugar–phosphate backbones lie on the outside of the molecule, and the purines and pyrimidines lie on the inside of the molecule. There is just enough space for one purine and one pyrimidine in the center of the double helix. The Watson–Crick model showed that the purine guanine (G) would fit nicely with the pyrimidine cytosine (C), forming three hydrogen bonds. The purine adenine (A) would fit nicely with the pyrimidine thymine (T), forming two hydrogen bonds. Thus A always pairs with T, and G always pairs with C. The three hydrogen bonds formed between G and C produce a relatively strong base pair. Because only two hydrogen bonds are formed between A and T, this weaker base pair is more easily broken. The difference in strengths between a G–C and an A–T base pair is important in the initiation and termination of RNA synthesis. The two chains of DNA are said to be antiparallel because they lie in the opposite orientation with respect to one another, with the 3’-hydroxyl terminus of one strand opposite the 5’-phosphate terminus of the second strand. The sugar–phosphate backbones do not completely conceal the bases inside. There are two grooves along the surface of the DNA molecule. One is wide and deep—the major groove—and the other is narrow and shallow—the minor groove (Fig. 4.4). Proteins can use the grooves to gain access to the bases. Page 8 ENGLISH FOR BIOLOGY Page 9 ENGLISH FOR BIOLOGY The Two DNA Chains Are Complementary A consequence of the base pairs formed between the two strands of DNA is that if the base sequence of one strand is known, then that of its partner can be inferred. A G in one strand will always be paired with a C in the other. Similarly an A will always pair with a T. The two strands are therefore said to be complementary. Different Forms of DNA The original Watson–Crick model of DNA is now called the B-form. In this form, the two strands of DNA form a right-handed helix. If viewed from either end, it turns in a clockwise direction. B-DNA is the predominant form in which DNA is found. Our genome, however, also contains several variations of the B- form double helix. One of these, Z-DNA, so-called because its backbone has a zig-zag shape, forms a left- handed helix and occurs when the DNA sequence is made of alternating purines and pyrimidines. Thus the structure adopted by DNA is a function of its base sequence. GROUP 3: DNA AS THE GENETIC MATERIAL Deoxyribonucleic acid carries the genetic information encoded in the sequence of the four bases—adenine, guanine, cytosine, and thymine. The information in DNA is transferred to its daughter molecules through replication (the duplication of DNA molecules) and subsequent cell division. DNA directs the synthesis of proteins through the intermediary molecule RNA. The DNA code is transferred to RNA by a process known as transcription. The RNA code is then translated into a sequence of amino acids during protein synthesis. This is the central dogma of molecular biology: DNA makes RNA makes protein. Retroviruses such as human immunodeficiency virus, the cause of AIDS, are an exception to this rule. As their name suggests, they reverse the normal order of data transfer. Inside the virus coat is a molecule of RNA plus an enzyme that can make DNA from an RNA template by the process known as reverse transcription. PACKAGING OF DNA MOLECULES INTO CHROMOSOMES Eukaryotic Chromosomes and Chromatin Structure A human cell contains 46 chromosomes (23 pairs), each of which is a single DNA molecule bundled up with various proteins. On average, each human chromosome contains about 1.3 × 10 8 base pairs (bp) of DNA. If the DNA in a human chromosome were stretched as far as it would go without breaking it would be about 5 cm long, so the 46 chromosomes in all represent about 2 m of DNA. The nucleus in which this DNA must be contained has a diameter of only about 10μm, so large amounts of DNA must be packaged into a small space. This represents a formidable problem that is dealt with by binding the DNA to proteins to form chromatin. As shown in Figure 4.5, the DNA double helix is packaged at both small and larger scales. In the first stage, shown on the right of the figure, the DNA double helix with a diameter of 2 nm is bound to proteins known as histones. Histones are positively charged because they contain high amounts of the amino acids arginine and lysine and bind tightly to the negatively charged phosphates on DNA. A 146 bp length of DNA is wound around a protein complex composed of two molecules each of four different histones—H2A, H2B, H3, and H4—to form a nucleosome. Because each nucleosome is separated from its neighbor by about 50 bp of linker DNA, this unfolded chromatin state looks like beads on a string when viewed in an electron microscope. Nucleosomes undergo further packaging. A fifth type of histone, H1, binds to the linker DNA and pulls the nucleosomes together helping to further coil the DNA into chromatin fibers 30 nm in diameter, which are referred to as 30-nm solenoids. The fibers then form loops with the help of a class of proteins known as nonhistones, and this further condenses the DNA (panels on left-hand side of Fig. 4.5) into a higher order set of Page 10 [...]... bacteria, or in the DNA or RNA of viruses An organism's genetic material Host cell (n): tế bào chủ - In biology, a host is an organism that harbors (cho ẩn náu) a virus or parasite Parasite (n): vât ký sinh Submicroscopic (adj): siêu hiển vi protein coat (n) : lớp bọc protein gene therapy (n) : liệu pháp gene - Gene therapy is a rapidly growing field of medicine in which genes are introduced into the... Vocabulary: Page 24 ENGLISH FOR BIOLOGY Express (v) –expression (n): biểu hiện, gene expression (n): biểu hiện gene Transcript (v) – transcription (n): phiên mã Sequence (v,n) – sequencing (n) : xác đònh trình tự - DNA sequencing technique Protein - coding gene (noun phrase) Gene (n) – genetic (adj) Exercise 6: DNA CLONING a introduce into (transfer into) b proteins c produced d.DNA cloning e the human... associated with Evoluationary (adj) – evolutionarily (adv): Alter (v) – alterative (adj) - alteration (n): sự thay đổi Mutate (v) – mutant (adj) - mutation (n): sự đột biến Proliferate (v) – proliferation (n): sinh sôi, nảy nở For instance = for example Insight Genotype -> phynotype (n) : kiểu hình GRAMMAR Page 28 ENGLISH FOR BIOLOGY Page 29 ENGLISH FOR BIOLOGY Page 30 ENGLISH FOR BIOLOGY Page 31 ENGLISH FOR