Download Topic 11 DNA intro - Manhasset Public Schools

Topic 11: Genetics Introduction
Name:
Genetics, Heredity and DNA Structure
Recall that the nucleus is a small organelle in a cell. There is only one in every cell,
and it is often called the "control center" because it controls all the activities of the cell
including cell reproduction, and heredity. How does it do this? The nucleus controls these
activities by the chromosomes. Chromosomes are microscopic, threadlike strands composed
of the chemical DNA (short for deoxyribonucleic acid). In simple terms, DNA controls the
production of proteins within the cell. These proteins in turn, form the structural units of
cells and control all chemical processes within the cell.
1. Why is the nucleus called the control center?
2. What are chromosomes and what are they made of?
3. What does DNA stand for?
4. What is the job of DNA?
5. What is the job of proteins?
Chromosomes are composed of genes. A gene is a segment of DNA that codes for a particular protein,
which in turn codes for a trait. Hence you hear it commonly referred to as the gene for baldness or the gene for
blue eyes. Meanwhile, DNA is the chemical that genes and chromosomes are made of. It stands for
deoxyribonucleic acid. DNA is called a nucleic acid because it was first found in the nucleus. The DNA in the
nucleus that actually controls the cell's workings. Heredity is the passing of genetic information from one
generation to the next through reproduction.
6. What is a chromosome?
7. Where are chromosomes located?
8. What is a gene?
9. What do genes code for?
10. Why is DNA called a nucleic acid?
11. What is heredity?
12. Put these terms in order from LARGEST to SMALLEST: gene, nucleus, chromosome:
In 1953, James Watson and Francis Crick established the structure of DNA. Just like how carbohydrates
are built by simple sugars linked together and proteins are built by amino acids linked together, DNA is a larger
molecule that has been synthesized by many subunits linked together. Recall that DNA is a nucleic, so DNA’s
building blocks are called nucleotides. Each subunit has three parts – a phosphate, a sugar and a base. The
subunits vary from one to another depending on the base it contains.
Nucleotide Structure
In the diagram on the right:
Color each phosphate one color
Color each sugar one color
Color each base (T,A,G,C) one color
When the nucleotides join together, the structure is a double helix, which is like a twisted ladder. The sides
of the ladder are made of alternating sugar and phosphate molecules. The sugar is deoxyribose. The rungs of
the ladder are pairs of 4 types of nitrogen bases: Adenine, guanine, thymine and cytosine. The bases are
known by their coded letters A, G, T, C. These bases always bond in a certain way as a pair to make the full
“step” of the ladder. Adenine will only bond to thymine. Guanine will only bond with cytosine. This is known
as the Base-Pair Rule. The bases can occur in any order along a strand of DNA. The order of these bases is the
code that contains the instructions. For instance ATGCACATA would code for a different gene than
AATTACGGA. A strand of DNA contains millions of bases. Note that the bases attach to the sides of the
ladder at the sugars and not the phosphate. The two sides of the DNA ladder are held together loosely
by hydrogen bonds.
13. What two scientists discovered the structure of DNA?
14. What are the subunits of DNA called ?
subunits:
15. What sugar is DNA made of?
16. What is the structure of DNA? What does it resemble?
17. What do the “sides of the ladder” consist of?
What are the three parts of these
18. What are the “steps” of the ladder composed of?
19. Name the 4 DNA bases:
20. Explain how the DNA bases are paired with one another:
21. How are the two sides of the ladder held together?
22. In the DNA Double Helix below, color the following:
•
Color the hydrogen bonds gray.
•
Color all the phosphates pink
(one is labeled with a "P").
•
Color all the deoxyriboses blue
(one is labeled with a "D").
•
Color the thymines orange.
•
Color the adenines green.
•
•
Color the guanines purple.
Color the cytosines yellow.
DNA - The Double Helix