Unit 1 – Notes #2 DNA Structure
Cellular Chemicals :
- All life forms are composed of at least one cell, anything smaller than a cell unit does not have life.
- A cell has all the equipment (organelles) needed to sustain life, provided that it is supplied with the correct chemicals.
- What is so unusual, is that living things are
made up of non-living chemicals.
- These chemicals can react with oxygen to release energy for the cell while other chemicals can be used as building materials for growth and repair.
- Many of these chemicals fit into three major nutrient groups:
1. Carbohydrates Ex. Sugars and starch
2. Lipids Ex. Oil and butter
3. Proteins Ex. Meat and cheese
Proteins :
- Unlike the first two groups, proteins are primarily used for building the structural components of a cell rather than providing energy for a cell.
- After protein molecules are ingested by an animal they are broken down into their tiny building blocks (20 different amino acids), these AA’s are then transported to the organisms cells.
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- The cell uses these amino acids to build new proteins for cells to grow and repair themselves as well as to make new cells through cell division (mitosis).
- The blue-prints and processes for building these proteins are quite intricate, and the control of protein synthesis is governed by the nucleus of the cell.
- If you think of a cell as being like a town, the nucleus would be like “City Hall”.
- Cells make a wide variety of proteins, by stringing these different AA’s into almost endless ways. Much like we can make a variety of words from just 26 letters of the alphabet.
- Each type of protein plays an important role in cellular activity and each protein must be built correctly to function properly.
- The blue-prints (genes) for these various proteins are found in the nucleus of the cell. These varying genes are found strung together on extremely long strands of DNA.
DNA : Deoxyribonucleic Acid
- Almost all body cells contain the full amount of DNA in their nucleus, so that they have the adequate amount of DNA to make other cells.
Exceptions:
1. Red Blood Cells do not have a nucleus when mature.
2. Sex Cells (Sperm and Egg) only have ½ the amount of DNA of a normal cell.
- The DNA molecule is the only molecule known that is capable of duplicating (replicating) itself.
- Most of the time, the DNA is found in the form of a long String called Chromatin.
- During cell division (mitosis), Chromatin bunches up to form Chromosomes.
- Humans have 46 chromosomes in each cell, but only 23 chromosomes in the sex cells.
- A section of a chromosome, which codes for a certain protein, is called a gene.
DNA Structure :
- All DNA, regardless of the type of organism, iscomposed of units called nucleotides, each nucleotide consists of the following 3 types of molecules:
A) a 5 carbon sugar called deoxyribose.
B) a phosphate group.
C) and one of four types of nitrogenous bases.
- These 3 molecules link together result in a nucleotide.
- There are 2 different categories of bases that stick off of the sugar part of the nucleotide:
1) Purines: (Adenine and Guanine)
-larger
-have 2 fused rings
2) Pyrimidines(Thymine and Cytosine)
- shorter
- have only one ring
- When the bases bond together to form the “rungs of the DNA ladder they do so in a set pattern. The alternating sugar and phosphates make up the rails (backbone). The bases make up the rungs.
- One Purine (an A or G) base always joins with one Pyrimidine (a C or T) base. This bonding of bases is called Complementary Base Pairing.
- Complementary Base Pairing is even more specific, because Adenine always bonds to Thymine, and Guanine always bonds to Cytosine.
A=T G=C
-If 2 purines bonded together they would be too long and they would overlap, and if 2 pyrimidines bonded together they would be too short.
- Weak Hydrogen bonds hold the 2 complementary bases together at the center of the DNA molecule.
- The complimentary strands link together to form a ladder, the ladder then twists to form what looks like a winding spiral staircase this is called a double helix.