Below you will find links to things that might be useful in your preparation for the biology EOC exam. Please spend some time looking over the different pages and resources linked here.
We will be covering the following topics:
December 2nd: Cycling of Matter - Procedure Writing December 9th: Cells and Biomolecules - Conclusion Writing December 16th: Genetics - Conclusion Writing January 6th: Genetics January 13th: Evolution January 20th: Ecology
Characteristics of the Genetic Code The genetic code has three other important characteristics.
The genetic code is the same in all living things. This shows that all organisms are related by descent from a common ancestor.
Each codon codes for just one amino acid (or start or stop). This is necessary so the correct amino acid is always selected.
Most amino acids are encoded by more than one codon. This is helpful. It reduces the risk of the wrong amino acid being selected if there is a mistake in the code.
Protein Synthesis The process in which proteins are made is called protein synthesis. It occurs in two main steps. The steps are transcription and translation. Watch this video for a good introduction to both steps of protein synthesis:
Transcription: DNA → RNA Transcription is the first step in protein synthesis. It takes place in the nucleus. During transcription, a strand of DNA is copied to make a strand of mRNA. How does this happen? It occurs by the following steps, as shown in Figurebelow.
An enzyme binds to the DNA. It signals the DNA to unwind.
After the DNA unwinds, the enzyme can read the bases in one of the DNA strands.
Using this strand of DNA as a template, nucleotides are joined together to make a complementary strand of mRNA. The mRNA contains bases that are complementary to the bases in the DNA strand.
Translation is the second step in protein synthesis. It is shown in Figurebelow. Translation takes place at a ribosome in the cytoplasm. During translation, the genetic code in mRNA is read to make a protein. Here’s how it works:
The molecule of mRNA leaves the nucleus and moves to a ribosome.
The ribosome consists of rRNA and proteins. It reads the sequence of codons in mRNA.
Molecules of tRNA bring amino acids to the ribosome in the correct sequence.
At the ribosome, the amino acids are joined together to form a chain of amino acids.
The chain of amino acids keeps growing until a stop codon is reached. Then the chain is released from the ribosome.
Causes of Mutations Mutations have many possible causes. Some mutations occur when a mistake is made during DNA replication or transcription. Other mutations occur because of environmental factors. Anything in the environment that causes a mutation is known as a mutagen. Examples of mutagens are shown in Figurebelow. They include ultraviolet rays in sunlight, chemicals in cigarette smoke, and certain viruses and bacteria.
Effects of Mutations Many mutations have no effect on the proteins they encode. These mutations are considered neutral. Occasionally, a mutation may make a protein even better than it was before. Or the protein might help the organism adapt to a new environment. These mutations are considered beneficial. An example is a mutation that helps bacteria resist antibiotics. Bacteria with the mutation increase in numbers, so the mutation becomes more common. Other mutations are harmful. They may even be deadly. Harmful mutations often result in a protein that no longer can do its job. Some harmful mutations cause cancer or other genetic disorders. Mutations also vary in their effects depending on whether they occur in gametes or in other cells of the body.
Mutations that occur in gametes can be passed on to offspring. An offspring that inherits a mutation in a gamete will have the mutation in all of its cells.
Mutations that occur in body cells cannot be passed on to offspring. They are confined to just one cell and its daughter cells. These mutations may have little effect on an organism.
Types of Mutations The effect of a mutation is likely to depend as well on the type of mutation that occurs.
A mutation that changes all or a large part of a chromosome is called a chromosomal mutation. This type of mutation tends to be very serious. Sometimes chromosomes are missing or extra copies are present. An example is the mutation that causes Down syndrome. In this case, there is an extra copy of one of the chromosomes.
Deleting or inserting a nitrogen base causes a frameshift mutation. All of the codons following the mutation are misread. This may be disastrous. To see why, consider this English-language analogy. Take the sentence “The big dog ate the red cat.” If the second letter of “big” is deleted, then the sentence becomes: “The bgd oga tet her edc at.” Deleting a single letter makes the rest of the sentence impossible to read.
Some mutations change just one or a few bases in DNA. A change in just one base is called a point mutation.
Day 3: Genetics Part 1
All living things have DNA. DNA is a molecule that forms a double stranded helix. The two strands of DNA are held together by hydrogen bonds between nucleotides. You are probably familiar with the nucleotides A, T, C, and G. Nucleotides A and T bind together and nucleotides G and C bind together. Below is an diagram of DNA.
DNA is important because it codes for all the different characteristics that make you, you. Everything in your cells in controlled by DNA. As all living things have DNA it means we are all controlled by our DNA. The order of nucleotides in your DNA determines your characteristics.
Inside of your cell your DNA is arranged into chromosomes. Chromosomes are coils of DNA. When a cell replicates it copies its DNA first so that each cell made can have a full copy of DNA. In human cells there are 23 pairs of chromosomes. You get one set of 23 chromosomes from your mom and one set of 23 chromosomes from your dad.
Chromosomes can be broken into chucks of DNA that are called Genes. Genes code for specific proteins. Proteins are things like hormones, enzymes, etc. They run the cell. Genes come in different forms, called alleles. An allele is a version of a gene.
Lets break it down. Genes are made of DNA. DNA codes for traits. So a portion of DNA that codes for your eye color is called a gene. But you might have DNA that codes for BLUE eye color. That type of gene is an allele. Another person might have an allele for BROWN eyes. You both have DNA. You both have genes. You both have genes for eye color. And yet one of you has the allele for brown eyes while the other has the allele for blue eyes.
But remember how we said that you have pairs of chromosomes, one from mom and one from dad. This means that each individual has 2 copies of every gene. You could have the same allele on each chromosome or you could have different alleles. If you have 2 copies of the same allele form then you are homozygous but if you have two different alleles then you are heterozygous. This will be important when we talk about passing down genetic traits.
Before we talk about how traits are passed down from one generation to the next let us discuss how traits are formed in the first place. When DNA is copied identical strands are formed. DNA is semi-conservative, which means that one strand is left intact and a new strand is built directly off the original. It works like this:
Because DNA is double stranded your original 2 strands are copied into 4 strands, which made 2 double stranded DNA molecules. Before a cell can divide a copy of the DNA must be made so that both daughter cells have their own copy of the DNA.
Cells divide constantly in organisms. In multicellular organisms cell division provides more cells so that the organism can grow and develop. In single celled organisms, cell division is a form of replication where the parent makes two exact copies of themselves. In either case, 1 cell divides into two identical cells called daughter cells.
The type of cell division shown above is called mitosis. This form of cell division occurs in body cells and single celled organisms alike. Another form of cell division makes sex cells (gametes). These cells only have half the DNA that the original cell had.
The first part of meiosis, the process that forms sex cells, is very similar to mitosis. The DNA has copied. However, When the chromosomes pair up in meiosis they sometimes trade portions of DNA. This mixes up the DNA so that each cell formed is a little bit different than the parent cells.
Also, rather than splitting once, like in mitosis, meiosis has two cell divisions. The result is that you end up with 4 daughter cells from one parent cell. Each daughter cell is different than the parents. Each daughter cell only has half the required amount of DNA. This is important because these cells will go on to be egg and sperm cells. They make each new generation of organisms and the variation that occurs in meiosis makes it so you are not exactly the same as your parents or your siblings.
Day 2: Cells and Biomolecules
There are 4 types of molecules that make of many of the structures and are responsible for the functions of living things. These molecules are:
Carbohydrates - Made of carbon, hydrogen, and oxygen. Carbohydrates store energy for organisms and also make up structures such as cell walls in plants.
Lipids - Lipid is another name for fat. Lipids are important as they store energy but they also are an important component of cell membranes.
Nucleic Acids - Nucleic acids form DNA, RNA, and ATP. ATP is the major energy storage molecule for all living things. DNA is the genetic code that is responsible for all characteristics of an organism. RNA is needed to make proteins. Nucleic acids contain nitrogen.
Proteins - Proteins are important because they allow molecules into and out of cells. They are also responsible for the chemical reactions that occur in organisms and they control the functions of living things. Proteins also contain nitrogen.
These biomolecules are important for life. All living things are made up of cells. Cells contain various structures that enable them to survive and have the characteristics of life such as taking in nutrients and reproduction. These structures are called organelles. Below is a table of the organelles and their functions that you should know. (please note that chloroplasts and a large central vacuole are only found in plant cells)
The cell membrane is also very important. Without the membrane the organelles would not be contained with the cell. The cell membrane has properties that allow it to function and support the cell.
Many Bacteria Cells Reproduce Through Binary Fission
Day 1: Cycling of Matter
The nitrogen cycle is the most complicated of the cycles and the newest to you. Below is a diagram of this cycle.
You will also need to be familiar with the Carbon/Oxygen Cycle. See diagram below.
One of the most important processes in the cycling of carbon is Photosynthesis. Photosynthesis is the process where plants take in carbon dioxide and water and release oxygen. This process makes sugar that the plant uses to build structures like cell walls and also as a storage molecule for energy. Below is the equation for photosynthesis.
Photosynthesis takes carbon dioxide from the air and stores it in plants. Photosynthesis occurs in the chloroplast of the cell. Only organisms that can make their own food have chloroplasts. The carbon can be recycled back into the atmosphere during cellular respiration. Cellular respiration is the reverse of photosynthesis. See the equation below.
Cellular respiration is performed by all living things. It occurs in the mitochondria of the cell. All organisms have mitochondria. ATP is a molecule that stores energy. It is this molecule that all organisms use to provide energy for their cells. This molecule provides the cell with energy to grow, to move molecules in and out of the cell, to move, etc.