Genetics - molecular structure


Text pages and Handouts you should have –
Reading:
· Pickering: pp 202-203
· Designer Genes hand out
Lab methods, results
· DNA extraction from cheek cell
Notes you should have:
· Beautiful DNA – the history of discovery
· Biologically Important Macromolecule: Nucleic acid
· DNA – Genes- mRNA – Proteins
· Gene mutations
· Sickle cell
Worksheets:
· Creating a DNA model
· Nucleic Acids; DNA and RNA
· DNA Crossword puzzle
· Genetic code worksheet
· From chromosomal nucleic acid to body proteins – dry lab
· Protein Synthesis

VOCABULARY:
nucleic acid, nucleotide, deoxyribonucleic acid (DNA), ribinucleic acid (RNA)
adenine, guanine, cytosine, thymine, uracil, ribose, deoxyribose,
hydrogen bonding, nitrogen base, double-ring purines, single-ring pyrimidines,
antiparallel, phosphate, complementary base pairing, transcription, mRNA,
translation, tRNA, ribosomes, eER, amino acid, protein

CELL REVIEW:




All membranes in the cell and around the cell contain proteins embedded amonst the lipid bi layer. Some proteins transport molecules during facillitated diffusion or in active transport. Some proteins are recocognition molecules that convey messages beteen the cell and its environment.
library.thinkquest.org/.../rna_translation.html
http://publications.nigms.nih.gov/thenewgenetics/chapter1.html#c1












The structure of DNA
DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone.


DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).
The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.
DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long antiparallel strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.
An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.

In addition, the DNA can be copied to produce a messenger molecule (mRNA) that can travel to the cytoplasm, where this information is translated into the appropriate proteins.


How Genes Work – protein synthesis


People have known for many years that living things inherit traits from their parents. That common-sense observation led to agriculture, the purposeful breeding and cultivation of animals and plants for desirable characteristics. Firming up the details took quite some time, though. Researchers did not understand exactly how traits were passed to the next generation until the middle of the 20th century.

Now it is clear that genes are what carry our traits through generations and that genes are made of deoxyribonucleic acid (DNA). But genes themselves don't do the actual work. Rather, they serve as instruction books for making functional molecules such as enzymes, hemoglobin etc = proteins, which perform the chemical reactions in our bodies.
Proteins do many other things, too. They provide the body's main building materials, forming the cell's architecture and structural components. But one thing proteins can't do is make copies of themselves. When a cell needs more proteins, it uses the manufacturing instructions coded in DNA.
The DNA code of a gene—the sequence of its individual DNA building blocks, labeled A (adenine), T (thymine), C (cytosine), and G (guanine) and collectively called nucleotides— spells out the exact order of a protein's building blocks, amino acids. For every 3 nucleotides, called a codon, a specific amino acid is added to form a protein .
Occasionally, there is a kind of typographical error in a gene's DNA sequence. This mistake— which can be a change, gap, or duplication—is called a mutation.
A mutation can cause a gene to encode a protein that works incorrectly or that doesn't work at all. Sometimes, the error means that no protein is made.
But not all DNA changes are harmful. Some mutations have no effect, and others produce new versions of proteins that may give a survival advantage to the organisms that have them. Over time, mutations supply the raw material from which new life form evolves.


Chromosomes contain the genetic code, which is translated into specific proteins required by the body Chromosomes have a molecular structure, which is translated into specific proteins required by the body

The molecular structure of chromosmes is nucleic acid, composed of nucleotide units

The molecular structure of protein is composed of amino acid units




The diagram below shows the chromosomal DNA in its replicated (duplicated form), which occurs before the cell makes a copy of itself in mitosis or meiosis. At other stages the chromosmes cannot be seen because they are more diffuse.
Chromosome, showing gene as a section of DNA
Chromosome, showing gene as a section of DNA

  • Be able to draw and label the following diagram


external image chromosome1.gif
external image chromosome1.gif



NUCLEIC ACIDS


  • Nucleotides are the momomer unit of deoxyribonucleic acid (DNA) and of ribonucleic acid (RNA)
Nucleotides of DNA consist of a phosphate group, a deoxyribose sugar and a nitrogen base: single structure pyrimadine = Cytosine or Thymine and a double ring purine = Adenine or Guanine
In the double helical structure adenine bonds with thymine, while guanine bonds with cytosine


nucleotide.gif
nucleotide.gif




The diagram below shows how the nucleotides are arranged in the DNA molecule.
  • The chains are antiparallel.
  • C and G are bonded through 3 hydrogen bonds
  • T and A are bonded through 2 hydrogen bonds
  • The chains are covalently bonded through the phospate and the sugar
    external image ch1_nucleotide.jpg
    external image ch1_nucleotide.jpg

























Text pages and Handouts you should have –
Reading:
· Pickering: pp 202-203
· Designer Genes
Lab methods, results
· DNA extraction from cheek cell
Notes:
· Beautiful DNA – the history of discovery
· Biologically Important Macromolecule: Nucleic acid
· DNA – Genes- mRNA – Proteins
· Gene mutations
· Sickle cell
Worksheets:
· Creating a DNA model
· Nucleic Acids; DNA and RNA
· DNA Crossword puzzle
· Genetic code worksheet
· From chromosomal nucleic acid to body proteins – dry lab
· Protein Synthesis


VOCABULARY:
nucleic acid, nucleotide, deoxyribonucleic acid (DNA), ribinucleic acid (RNA)
adenine, guanine, cytosine, thymine, uracil, ribose, deoxyribose,
hydrogen bonding, nitrogen base, double-ring purines, single-ring pyrimidines,
antiparallel, phosphate, complementary base pairing, transcription, mRNA,
translation, tRNA, ribosomes, eER, amino acid, protein

CELL REVIEW:




All membranes in the cell and around the cell contain proteins embedded amonst the lipid bi layer. Some proteins transport molecules during facillitated diffusion or in active transport. Some proteins are recocognition molecules that convey messages beteen the cell and its environment.
library.thinkquest.org/.../rna_translation.html
http://publications.nigms.nih.gov/thenewgenetics/chapter1.html#c1












The structure of DNA
DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone.


DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called **mitochondrial DNA** or mtDNA).
The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.
DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long antiparallel strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.
An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.

In addition, the DNA can be copied to produce a messenger molecule (mRNA) that can travel to the cytoplasm, where this information is translated into the appropriate proteins.


How Genes Work – protein synthesis


People have known for many years that living things inherit traits from their parents. That common-sense observation led to agriculture, the purposeful breeding and cultivation of animals and plants for desirable characteristics. Firming up the details took quite some time, though. Researchers did not understand exactly how traits were passed to the next generation until the middle of the 20th century.

Now it is clear that **genes** are what carry our traits through generations and that genes are made of **deoxyribonucleic acid (DNA)**. But genes themselves don't do the actual work. Rather, they serve as instruction books for making functional molecules such as enzymes, hemoglobin etc = **proteins**, which perform the chemical reactions in our bodies.
Proteins do many other things, too. They provide the body's main building materials, forming the cell's architecture and structural components. But one thing proteins can't do is make copies of themselves. When a cell needs more proteins, it uses the manufacturing instructions coded in DNA.
The DNA code of a gene—the sequence of its individual DNA building blocks, labeled A (adenine), T (thymine), C (cytosine), and G (guanine) and collectively called **nucleotides**— spells out the exact order of a protein's building blocks, **amino acids**. For every 3 nucleotides, called a codon, a specific amino acid is added to form a protein .
Occasionally, there is a kind of typographical error in a gene's DNA sequence. This mistake— which can be a change, gap, or duplication—is called a mutation.
A mutation can cause a gene to encode a protein that works incorrectly or that doesn't work at all. Sometimes, the error means that no protein is made.
But not all DNA changes are harmful. Some mutations have no effect, and others produce new versions of proteins that may give a survival advantage to the organisms that have them. Over time, mutations supply the raw material from which new life form evolves.





Genes and Alleles

Some characteristics, such as eye colour and the shape of the earlobe, are controlled by a single gene. These genes may have different forms.
Different forms of the same gene are called
**allele** [allele: alternative form of a gene]. The gene for eye colour has an allele for blue eye colour and an allele for brown eye colour.
]:
individual A is heterozygous and has one allele for blue eyes (recessive). B is homozygous and has two alleles for brown eyes (dominant). C is homozygous recessive and has two alleles for blue eyes (recessive)
individual A is heterozygous and has one allele for blue eyes (recessive). B is homozygous and has two alleles for brown eyes (dominant). C is homozygous recessive and has two alleles for blue eyes (recessive)


external image 4241_RCMhelix.jpg

MAKING PROTEINS: Protein synthesis

So, we've described DNA—its basic properties and how our bodies make more of it. But how does DNA serve as the language of life? How do you get a protein from a gene?
There are two major steps in making a protein. The first is
transcription
, where the information coded in DNA is copied into RNA.
The RNA nucleotides are complementary to those on the DNA: a C on the RNA strand matches a G on the DNA strand.
The only difference is that RNA pairs a nucleotide called uracil (U), instead of a T, with an A on the DNA.
A protein enzyme called
RNA polymerase
reads the DNA and makes the RNA copy. This copy is called messenger RNA, or mRNA, because it
delivers the gene's message to the protein-producing machinery in the cytoplasm - rER..
At this point you may be wondering why all of the cells in the human body aren't exactly alike, since they all contain the same DNA.
What makes a liver cell different from a brain cell? How do the cells in the heart make the organ contract, but those in skin allow us to sweat?
Cells can look and act differently, and do entirely different jobs, because each cell "turns on," or expresses, only the genes appropriate for what it needs to do.

Researchers discovered that molecules of RNA polymerase behave like battery-powered spiders as they crawl along the DNA ladder, adding nucleotides one at a time to the growing RNA strand.



Step 2: RNA Translation

After the mRNA has been transported to the **rough endoplasmic reticulum**, it is fed into the ribosomal translation machineries.
To convert the mRNA into protein, tRNA is used to read the mRNA sequence, 3 nucleotides at a time.

Amino acids are represented by codons, which are 3-nucleotide RNA sequences. The mRNA sequence is matched three nucleotides at a time to a
complementary set of three nucleotides in the anticodon region of the corresponding


To convert the mRNA into protein, tRNA is used to read the mRNA sequence, 3 nucleotides at a time.
Amino acids are represented by codons, which are 3-nucleotide RNA sequences.
The mRNA sequence is matched three nucleotides at a time to a complementary set of three nucleotides in the anticodon region of the corresponding tRNA molecule.
Opposite the anticodon region of each tRNA, an amino acid is attached and as the mRNA is read off, the amino acids on each tRNA are joined together through peptide bonds.





Mutations:


What is a mutation?

Changes in the genetic material (DNA).
There are two types of mutations that can occur in gamete cells:
1.
Gene Mutations
2. Chromosomal Mutations

EXAMPLE of a gene mutation:


DNA: TAC GTA TGG AAT
mRNA: AUG CAU ACC UUA
Amino Acid: Met - His - Thr - Leu
Chromosomal Mutation
Non-disjunction: Means “not coming apart”. When homologous chromosomes fail to separate properly during meiosis.

.
external image image006.jpg
external image image006.jpg

Results in abnormal numbers of chromosomes.
Trisomy means a person has an extra copy of a chromosome.
Monosomy means a person is missing a copy of a chromosome.


Know examples: Triisomy 21 - Down's Syndrome and Klinefelter's syndrome, that is XXY