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Chromosomes, Genes and DNA

Science, Grade 6


Table Of Contents: Chromosomes, Genes and DNA

1. Chromosomes

2.1. Chromosome Location
Pairs of chromosomes are found in the nucleus of a cell. One chromosome from each pair is inherited from each parent.
2.2. Composition of Chromosomes
Chromosomes are made up of DNA (deoxyribonucleic acid), the hereditary material in humans and most other organisms.
2.3. Four Nitrogen Bases
The hereditary information in DNA is stored as a code of four nitrogen bases: adenine, guanine, cytosine, and thymine.
2.4. What Is a Gene?
Specific sections of the DNA are called genes. Each gene provides the cell with different information.
2.5. Number of Human Genes
Each chromosome is made up of many genes. There are about 100,000 genes found on human chromosomes.
2.6. Chromosome Number in Humans
In each human body cell, there are 46 chromosomes, existing in 23 pairs.

2. Genes

3.1. Function of a Gene
Each gene along a strand of DNA has the information to tell the cell to produce a specific protein.
3.2. DNA Sequence
A gene is made up of a particular sequence of DNA bases. This sequence acts as a code for a protein.
3.3. What Is a Trait?
The production of different proteins determines the traits of an organism. A trait is an inherited characteristic.
3.4. Alleles
Genes that exist in alternate forms are called alleles. The gene that determines earlobe shape exists in two alleles—one results in an attached earlobe and the other a free earlobe.
3.5. Multiple Alleles
Some genes have more than two, or multiple alleles. The human ABO blood group gene has three alleles that can combine to four types of blood groups.

3. DNA

4.1. DNA Shape and Composition
Double-stranded DNA (deoxyribonucleic acid) has a twisted ladder-like shape called a double helix. Each DNA strand is composed of a series of nucleotides.
4.2. Parts of a Nucleotide
A nucleotide contains a sugar, phosphate, and nitrogen base—adenine (A), guanine(G), cytosine(C), or thymine(T).
4.3. Complementary Base Pairs
The nitrogen bases pair with each other, adenine with thymine and cytosine with guanine. These are called complementary base pairs.
4.4. Role of DNA in Replication
The sequence of these DNA nitrogen bases provides a code. The code serves as a template when DNA is copied in a process called replication.
4.5. Role of DNA in Transcription
In a similar process called transcription, the DNA code is used to make RNA (ribonucleic acid).

4. Pause and Interact

5.1. Review
Use the whiteboard tools to complete the activity.
5.2. Chromosome and DNA Structure
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.

5. Overview: From DNA to Protein

6.1. Protein Formation
To make a protein, a gene's DNA sequence is transcribed to a strand of RNA. Then the RNA is translated into a chain of amino acids by a ribosome, and a protein is formed.

6. Pause and Interact

7.1. From DNA to Protein
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.

7. DNA Transcription: DNA to RNA

8.1. Process of Transcription
During the process of transcription a DNA gene sequence is copied to a single RNA (ribonucleic acid) strand called a messenger RNA, or mRNA.
8.2. DNA Unwinds
Transcription starts when double-stranded DNA unwinds and exposes a sequence of nitrogen bases.
8.3. Formation of RNA
A new strand of complementary bases forms to create RNA.
8.4. RNA Contains Uracil, Not Thymine
The structure of RNA is similar to DNA, but it uses the nitrogen base uracil instead of thymine.
8.5. RNA Travels to the Cytoplasm
The messenger RNA carries the code to the ribosomes in the cytoplasm.

8. Translation: RNA to Protein

9.1. What Is Translation?
The process of converting the coded information on the messenger RNA to a protein is called translation.
9.2. Messenger RNA Attaches to a Ribosome
The mRNA travels through a nuclear pore to the cytoplasm and attaches to a ribosome. The ribosome moves along the mRNA strand, translating the code.
9.3. Messenger RNA Codons
Three sequential mRNA bases form a triplet code for a particular amino acid. Each triplet is called a codon.
9.4. Transfer RNA
Another type of RNA called transfer RNA (tRNA) carries specific amino acids.
9.5. Anticodons
Every tRNA has an anticodon region that is complementary to a specific codon on the mRNA.
9.6. Amino Acid Chain
Each time a tRNA anticodon and codon pair, an amino acid is added to a chain that eventually forms a specific protein.
9.7. Transfer RNA Molecules Work Together
Many tRNA molecules and ribosomes work together at the same time along one strand mRNA.

9. The Genetic Code

10.1. What Is the Genetic Code?
The correspondence between the RNA triplets or codons and specific amino acids that are used to form a particular protein is called the genetic code.
10.2. UUC Codes for Phenylalanine
For example, the triplet code UUC on a messenger RNA always pairs with the transfer RNA that carries the amino acid phenylalanine.
10.3. Genetic Code Table
This is the Genetic Code table. Find the codon UUC by starting with the left column, then going across the top, and then down the right column. UUC corresponds to the amino acid phenylalanine.
10.4. Universal Nature of the Genetic Code
The genetic code is the same in nearly all organisms.

10. Pause and Interact

11.1. Review
Use the whiteboard tools to complete the activity.
11.2. Deciphering the DNA Code
Follow the onscreen instructions.

11. Mutations

12.1. What Is a Mutation?
A mutation is a change that occurs in a gene or chromosome that can cause incorrect or different proteins to be made and alter an organism's normal trait.
12.2. Types of Mutations
A mutation in the DNA can occur when a single base pair is changed, removed, or added. Mutations can also happen when large sections of DNA are altered.
12.3. Mutations During Meiosis
Other mutations happen when the chromosomes don't separate properly during meiosis. Sex cells can end up with more or less than the normal number of chromosomes.
12.4. Harmful and Helpful Mutations
Mutations are harmful if they decrease an organism's ability to survive or reproduce. Other mutations can be helpful. Mutations are often inherited and introduce changes in a species.

12. Vocabulary Review

13.1. Chromosomes, Genes and DNA Vocabulary Matching
Use the whiteboard tools to complete the activity.

13. Virtual Investigation

14.1. Building DNA and RNA
Before mitosis begins, a cell doubles its amount of chromosomes by replicating, or copying all of its DNA. During replication, double-stranded DNA unwinds and each strand acts as a template for a new strand. DNA transcription is a similar process except only a part of the DNA sequence is copied to form a messenger RNA (mRNA) strand. In this investigation you will build new strands of DNA and RNA using nitrogen bases, sugars and phospates to create the nucleotide sequence. Remember, during replication when you are copying DNA, you must build two new strands of DNA, but during transcription only a single strand of RNA is built. Choose Build DNA or Build RNA to begin the investigation.

14. Assessment

15.1. Chromosomes, Genes, and DNA
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