DNA STRUCTURE AND REPLICATION NOTES DNA stands for ___________________________________________ It is the “blueprint for life”; everyone’s DNA is different! Each ________________________________ codes for a protein that will represent a ________. DNA is found in the ____________________ of __________________ cells.
History of DNA Discovery Rosalind Franklin (1950) - Used X-ray diffraction to show DNA fibers were “twisted”. This was one smart lady!
Erwin Chargaff (1952) - DNA is composed of “nucleotides” bonded together in a paired fashion: Chargaff’s base pair rule: _____________ (A) with _______________ (T) ______________ (C) with ______________ (G) Using all the accumulated knowledge from previous scientists’ in 1953 James Watson & Francis Crick published their findings on the structure of DNA. They called this structure a _______________ ________________. **They won the Nobel Prize in 1962. Watson & Crick’s findings: DNA is composed of two nucleotide chains arranged in a ________________________(twisted ladder) Nucleotides combine together, across the ladder, in complementary base pairing:___ ___ and ___ ___. Nucleotides are held together by weak ____________ ____________. DNA is found only in the _________________ It is composed of subunits called________________, which are the building blocks of all nucleic acids.
The DNA nucleotide is made up of three different components:_______________________________, a _________________________, and one of four _____________ ___________: adenine, guanine, thymine, and cytosine (A-T, G-C) Adenine and guanine are double-ringed molecules known as____________________, while cytosine and Thymine are single-ringed____________________. The general structure of a nucleotide is shown in Figure 1 below. Notice where the phosphate and the base bond to the sugar.
Figure 1: Structure of a nucleotide is circled and labeled. The DNA Molecule It is “___________________________.” (See Figure 1 or 2 on next page) It is made up of two strands of nucleotides paired with one another, giving it a “ladder-like” structure. The “______________” of the “______________” are composed of alternating units of _______________________________________& _____________________________ connected together by ____________________________ (strong bonds) to form the “_____________________” of the molecule. The phosphates connect to the 5’ of one sugar to the 3’ of the next sugar. The two sides of the molecule are identical except that they run in opposite directions. The two strands are said to be ____________________________to one another.
The “_______________” of the DNA “_____________________” are composed of the _____________________________which are bonded to the deoxyribose sugar & project out into the center of the molecule where they pair with one another. The chemical structure of the nitrogen bases limits their pairing to very specific combinations. This pairing of the bases is referred to as __________________________________base pairing. (refer to figure 2 below) o ________________________on one strand will always pair only with ___________________on the opposite strand. o ________________________on one strand will always pair with ____________________ on the opposite strand. The two strands are held together by weak ___________________________that form between the bases. Adenine & Thymine form _______ hydrogen bonds, while guanine & cytosine form ________ hydrogen bonds. (refer to figure 2 below) Watson & Crick described DNA as a _______________________________ because the two strands of nucleotides are twisted around one another in a spiral.
Figure 2: Structure of DNA 5’
Exercise 1: Structure of DNA 1. Refer to Exercise 1 on the data sheet. On the diagram provided, a DNA molecule will be drawn, colored, & labeled. 2. Note that the sugar/phosphate “backbones” of the two strands are already drawn. First, they must be colored & labeled. Color the deoxyribose sugars purple & color the phosphates pink. 3. Now label each sugar with a “D” and each phosphate with a “P”. Label the 3’ & 5’ ends of the strands using Figure 2 as a guide. 4. Now, complete the DNA molecule by adding the nitrogen bases to the strand. The first pair is already drawn. Using the templates shown below, finish drawing in the remaining 8 bases on the left side of the DNA diagram. The bases can be placed on the strand in any order, but make sure you use at least one of each type. Note that the bases are attached to the sugars, NOT the phosphates. Also, allow enough room between the bases to indicate the hydrogen bonds (Step 7).
A Adenine (Red)
G Guanine (green)
T Thymine (Yellow)
C Cytosine (Blue)
5. Next, draw in the complementary bases on the right side of the DNA diagram. Remember, the bases drawn must be complementary to the ones already drawn on the left side. 6. Color the bases as indicated above & label each one with the first letter of the name of the base (A, T, G, C). 7. Now indicate the hydrogen bonds between all the base pairs using dotted lines. Place 2 dotted lines between A and T, and 3 dotted lines between G & C. 8. Finally, somewhere near the middle of the molecule, draw a circle around a single nucleotide on each strand and label them “nucleotide”.
PART 2: REPLICATION OF DNA DNA is the “____________________________” for an organism. The specific arrangement o sequence of the paired nitrogen bases in the DNA molecule makes up the “_______________________” in the cell. The DNA molecules must be able to produce ____________________________of itself prior to ___________________________________in order to ensure that: (1) the ___________________information is carried from generation to generation, and (2) each new cell will have the _______________same genetic information. The process by which the DNA molecule is copied is called __________________________. DNA replication has been shown experimentally to be a “_________________________________” process which means that at the completion of replication each new DNA molecule consists of one strand from the ______________________DNA molecule and one _____________synthesized strand.
THE STEPS OF DNA REPLICATION ARE AS FOLLOWS: 1. The two original strands composing the DNA double helix____________________. 2. The weak hydrogen bonds are broken by the enzyme __________________ exposing the nitrogen bases. 3. As this occurs, each of the two strands acts as a “______________________” or mold for the replication of a new strand. 4. New nucleotide bases are attracted to their ___________________________partners on each of the separated strands and pair with them forming ______________________bonds. 5. Two _______________ molecules of DNA are formed, each made of a __________and _____________strand (semi-conservative). In step 3, as the new nucleotides come in and pair, an enzyme, __________________________, moves along each newly forming strand, catalyzing the formation of ______________________bonds between the _____________and phosphates of the new nucleotides. DNA polymerase can only move in a _________________direction. (See Figure 4). One of the new strands is synthesized____________________, in one long unbroken piece in the 5’ to 3’ direction. This is called the “__________________________” and has ______________________________replication. The DNA polymerase enzyme does not act on the second strand until a stretch of about __________________nucleotides has been exposed. Then it starts at the replicating fork and moves along, in the __________________________direction, until the 100-300 nucleotides are paired. This is the “_______________________________” and it has ________________________________replication.
When another such section of nucleotides of the DNA has opened, the process is repeated. This results in a series of short replicated pieces called _______________________fragments, which are later connected together by ligase enzyme.
SUMMARY: during replication, the leading strand has continuous replication (into fork) and the lagging strand has discontinuous replication (out of fork) in the opposite direction. FYI- Origins of replication- There are many different sites along a chromosome which are active in replication. There may be 100’s or 1000’s of initiation points along one DNA molecule- about 50,000 to 300,000 nucleotide pairs long (15 to 100 um). A single chromosome is huge. The “X” chromosome is 29,850,000 base pairs in length. (DNA polymerase can hook about 50 nucleotides together in a second in mammals.)
3’ Figure 4: Continuous & Discontinuous Strands
Continuous (leading) strand
Discontinuous (lagging) strand
Exercise 2: Replication 1. Using the DNA sequence that was constructed in Exercise 1, the replication of the molecule will be illustrated. 2. In Exercise 2 on the data sheet, the strands of DNA are shown to be splitting apart as the base pairs are separated in preparation for replication. The shorter strands in the center represent the new strands that are being synthesized off the original template. The arrows on the diagram indicate the direction that DNA polymerase is moving down the strands as it joins the new nucleotides together. 3. On the original DNA strands (that are splitting apart; the outside strands) draw in the same bases that were used in Exercise 1. On the shorter strands (newly synthesized) draw in bases that are complementary to those in the original DNA template. 4. Color and label all the components in the diagram, using the same colors as in Exercise 1. 5. Indicate hydrogen bonds between all the paired bases as in Exercise 1. 6. Label the continuous strand & the discontinuous strand. Also label the 3’ and 5’ ends of the original strands and of each new strand being synthesized.
PAP 2014: The Cell Cycle & Cancer As we have already learned, the _____________ theory states that all cells come from preexisting _____________. In this unit you will learn how cells reproduce to make ________________ daughter cells. What role does cellular division play in the lives of organism? 1. _______________________________: when a unicellular organism such as an amoeba divides, it reproduces an entire organism. The two organisms are identical. 2. _________________ and __________________________: in multicellular organisms, cell division allows for growth (from a single, fertilized egg) and repair of the organism. It is important to note that cells do not simply “pinch” in half. A dividing cell duplicates its DNA and sends each identical copy to two ends of the cell and then splits into two ________________________ cells. All of a cell’s hereditary information is called its _________________. A typical human cell has about ______ feet of DNA!! Before the cell can divide, all of this genome must be copied so that each daughter cell can have its own copy. The replication and distribution of this DNA is possible because the DNA is packaged into __________________. Chromosomes are made of the chromatin material that we have been studying. During cell division, they condense and appear as chromosomes.
Every type of organism has a characteristic number of chromosomes. Human have _____ chromosomes in the nucleus of their _______or body cells (every cell but the ______ and (______________). Reproductive cells or __________________have half of that number, _______________. The diagram above illustrates that each chromosome is made up of two _________________________. Each contains the identical copies of the cell’s DNA. These copies are held together at the “waist” by the ________________. A cell with that is about to divide has double the amount of DNA and is referred to as ____________ or 2N. At the end of cell division the cell only has one copy of DNA and it is referred to as ____________ or N.
The Cell Cycle:
The diagram above represents the life of a cell. The G1, S period, and G2 in the above diagram is called ___________________________ and accounts for ________% of the cell’s life. During interphase the cell grows and copies its chromosomes in preparation for cell division. Mitosis is the division of the nucleus of the cell. Cytokenisis is the division of the _______________.
Interphase: (________________________) Cells are carrying out their normal functions in the body and preparing for cell division. This phase may be divided into three parts: 1. G1 phase: period of cellular __________________ and development. 2. S phase: ____________________________________ 3. G2 phase: manufacture of _____________ and ___________ needed for cell division.
Mitosis begins!! P.M.A.T. 1. __________________ (prepare) a. Chromatin appears as _________________. b. Nuclear membrane ______________. c. Nucleolus ________________. d. Spindle fibers __________________. e. Centrioles move to the ____________. At this point is the cell’s DNA, diploid or haploid?__________ 2. ____________________ (middle) a. Chromosomes _____________________ ____________________________ ____________________________ b. Spindle fibers ______________________ ____________________________ ____________________________
3. ____________________ (away) a. Chromatids ________________________ _____________________________ _____________________________ Each chromatid is now considered an individual chromosome.
4. ________________________ (two new cells) a. Nuclear membrane _________________. b. Nucleolus _____________________. c. Chromatids become __________________. d. Spindle fibers ________________.
At this point is the DNA in the new cells diploid or haploid? __________
How are plant and animal cells different in cell division? Plant cells
Cytokinesis is the ___________________________________________. In animal cells, a _________________ ________________ forms that pinches the cell in two.
In plant cells, there in no cleavage furrow. Instead, packets or ______________ from the Golgi body move to the center of the cell where they form a _____________ ___________. Cell wall materials collect here as the plate grows until a new cell wall has developed between the two daughter cells.
Cell Cycle Regulators & Cancer Regulating Cell Growth- Cyclins – Proteins that control the “____________” of the cell cycle (Mitosis!) ____________________occur at end of each cycle before it moves onto next phase. They ensure that the cell is healthy before allowing it to move onto next phase.
What stops cells from dividing endlessly? Internal regulators – Class of proteins that respond to events ___________ the cell called _____________. •
Checkpoint example: Some cyclins do not let cell continue the cell cycle (Mitosis) until all chromosomes are copies.
External regulators – Class of proteins that respond to events ___________ of the cell. Especially important in embryonic development and wound healing. What is Cancer? ____________________________________. Cell won’t stop dividing and eventually they block nutrients, oxygen and blood flow from tissues. *on a microscope slide you would see an abnormally high amount of cells going through mitosis. Environmental or genetic mutations disrupt healthy cell division. Environmental: over exposure to ______________, ________________, or sun! Genetic Mutations: chance mutations that occur during cell division. Can’t prevent How do tumors form? Cancer does not respond to the ____________ or ____________ regulators of a normal cell cycle. Cancer is essentially uncontrolled cell division and results in tumors over time that can disrupt.