MOLECULAR GENETICS

I. WHAT IS A GENE MADE OF?

DNA--Deoxyribonucleic Acid

* the last type of organic (contains carbon and hydrogen) molecule, DNA is a NUCLEIC ACID; remember carbohydrates (CHO, 2H:1O, used for energy), lipids (CHO, lots of H, high energy), and proteins (CHON, sometimes S)
* the genetic material which is copied and passed from generation to generation of cells/organisms
* controls the activity of cells/organisms by having the "code" for enzymes (proteins that are organic catalysts)
* DNA is DNA is DNA--all life as we know it contains DNA

STRUCTURE OF DNA

it is a polymer (a molecule consisting of many smaller repeating units) called nucleotides (for carbohydrates--the building blocks are glucose, a monosaccharide; for proteins--the building blocks are amino acids)

* each nucleotides has 3 parts:

1) a phosphate group (like ATP)
2) a 5-carbon sugar called deoxyribose (remember -ose)
3) 1 of 4 possible nitrogenous bases (A,T,C,or G); each nucleotide is named after the nitrogenous base it contains

* each phosphate connects to a deoxyribose (sugar) in a "chain"

* there are two chains in a molecule of DNA; called complementary chains
* each side of the chain is a side of the ladder, where the nitrogenous bases are like the steps

Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)

* in DNA, the nitrogenous bases are matched together and held by weak hydrogen bonds

adenine to thymine A <---> T
cytosine to guanine C <---> G

* so wherever there is an A--adenine on one chain, the other chain must have a T--thymine
* when these chains link together, the ladder twists, forming a DOUBLE HELIX

* the double helix shape was discovered by James Watson and Francis Crick
* this model best explains the actions of genes:

a) replication (duplication) during mitosis and meiosis
b) controlling the production of proteins

II. HOW DNA IS COPIED

* DNA maintains continuity (composition, order) by a process called REPLICATION (which means duplication)
* replication occurs during mitosis and meiosis during interphase; when chromosomes double
* here's how:

1) the DNA "unwinds" or "unzips" between the nitrogenous base pairs (breaks the hydrogen bonds)

2) free nucleotides found in the nucleus match up according to the following pattern:

A with T
T with A
C with G

G with C

* this occurs until all of the DNA is copied to form 2 double helices

Molecular Genetics

everything genetics related--all rolled into one
featured in class, this interactive activity zooms in on DNA from the level of organism on down through cells
an advanced simulation that shows how you can find your own genetic fingerprint
use DNA fingerprinting to find out who stole the lollipop! a MUST SEE!!!
all the molecular genetics material on this website; if you think you know your stuff, try this after completing the packet; includes a 30-question multiple choice quiz
Tim and Moby discuss DNA.
Check your knowledge on the structure of DNA.
practice your base pairing
watch how DNA is replicated (copied)
watch how DNA is replicated (copied)

as always, the Lew-Port Bio website kicks butt! watch DNA replication...
Check your knowledge of DNA replication.

III. THE GENETIC CODE

* each strand of DNA has about 3 billion nucleotides which code for proteins
* the building blocks of proteins are amino acids
* every 3 nucleotides code for an amino acid; this is called a CODON (found on mRNA)

TAGCTTAAACGT

there are 4 codons above

* different combinations of nucleotides code for different amino acids
* to make proteins, we must first make RNA in the nucleus

DIFFERENT CODES (CODONS) FOR DIFFERENT AMINO ACIDS

RNA--Ribonucleic Acid

* ribonucleic acid (RNA) is a lot like deoxyribonucleic acid (it is made up of 3-part nucleotides), but there are 3 differences:
1) RNA has ribose as the sugar instead of deoxyribose
2) has one chain--not a double helix
3) has Uracil (U) instead of Thymine (T)

 

* there are also 3 different kinds of RNA

mRNA (messenger RNA)- "copies" and "carries" the genetic code out from the nucleus; only one strand!

rRNA (ribosomal RNA)- the framework for the ribosomes, which synthesize proteins

tRNA (transfer RNA)- transports amino acids from the cytoplasm to the ribosomes to build proteins

 

Molecular Genetics

see how different codons code for different amino acids
highly advanced look at our genetic code; features a lot of topics not covered in Regents biology, but in college courses
Check your knowledge of the genetic code.

IV. PROTEIN SYNTHESIS: TRANSCRIPTION AND TRANSLATION

A) TRANSCRIPTION
* the process of making mRNA from DNA
* DNA is a template for the production of mRNA
* this occurs in the nucleus ONLY!

1) first, the DNA must be "unzipped" (just like replication)

2) then, in the nucleus, free RNA nucleotides link up with the template DNA in this pattern:

DNA RNA
A -----> U
C -----> G
G -----> C
T -----> A

3) the now formed single strand of mRNA now carries the genetic code and leaves the nucleus to the ribosomes in the cytoplasm; the DNA "re-zips" back up to the double helix

the code must now be changed into a protein...it must be TRANSLATED into a protein
B) TRANSLATION

1) the mRNA from transcription in the nucleus, then moves to the cytoplasm; DNA never leaves the nucleus!

2) mRNA meets up with the ribosomes (which are made up of rRNA), the protein factory

3) tRNA brings amino acids to the ribosome from the cytoplasm and matches them up to the RNA; the tRNA matches up with the mRNA--the codon on the mRNA links up with the anticodon on the tRNA;

4) each new amino acid is bonded to the others by dehydration synthesis, forming a chain of amino acids--a POLYPEPTIDE (remember the peptide bond is formed between amino acids)

followed by:

 

Molecular Genetics

too cool to wait until the end, here is the basics of protien synthesis
a comprehensive guide to all things involving genetics; focus on the: What is a protein? question download it as a stand alone demo here
watch how DNA is transcribed into mRNA
great advanced look at how DNA gets transcribed into mRNA
made for Regents biology, this is a must see animation/ description of protein synthesis; featured in class
Check your knowledge on translation.
an overall look at cellular functions featuring how protiens are made; a great summary of cell functions; shown in class
a narrated advanced look at how mRNA gets translated into proteins
watch how mRNA is translated into a polypeptide
Check your knowledge on translation.
featured in class, this is a great interactive site to see how DNA is copied and how proteins are synthesized

V. ONE GENE--ONE POLYPEPTIDE HYPOTHESIS

What is a gene? We asked this question before...now we can answer this in more detail.

GENE:
* a section of DNA that has the code for one polypeptide
* proteins are made up of one or more polypeptides (like hemoglobin)
* so, genes make proteins by holding the code for polypeptides
* the way the polypeptides fold together determines the function of the protein


* if a certain protein is needed by the organism, the stretch of DNA that holds the polypeptides for that protein get switched on; when not needed, it is switched off

GENE MUTATION (revisited):
* so, a gene mutation (like the one that causes polydactyly, sickle-cell anemia, Tay Sachs, PKU) is when the base sequence (A,T,C,G) of DNA is altered...

...which changes the mRNA codon during transcription...

...which codes for the wrong amino acid...

...which produces an abnormal protein!!!

* gene mutations are caused by mutagenic agents (mutagens)

VI. DNA & INDIVIDUALITY

* DNA codes for proteins

* some sequences are the same for mostly everyone (hemoglobin, blood antigen A, ribosomal rRNA)
* some are different (eye color, nose shape, different enzymes)

THESE DIFFERENCES MAKE YOU WHO YOU ARE!!!

Molecular Genetics
a great interactive site to show how a mutation leads to a different protein
see how point mutations affect proteins
see how different codons code for different amino acids

VII. GENETIC ENGINEERING

Because DNA is the same for all organisms, the DNA of one organism can be "cut and pasted" into the DNA of another organism. The organism who received this sequence of DNA will follow this code! By using genetic engineering, we have been able to produce important chemicals such as insulin, interferon (a cancer fighting protein), and human growth hormone (GH) in large quantities in bacteria! You can also modify the genome of organisms to possibly correct genetic defects or agriculturally desirable plants and animals.

recombinant DNA

* modified DNA strands that is produced when a small piece of DNA is added to the genome (DNA molecule) of another organism
* will produce the polypeptide (protein) it codes for
* organisms that contain recombinant DNA are called TRANSGENIC ORGANISMS

* restriction enzymes can "cut" specific pieces of the DNA molecule (ex. AATT); also called called gene splicing

* other enzymes can "paste" the DNA back together

Here's an examplet how...
1) restriction enzymes are used to "cut" certain sequences of DNA

2) genes that are important (ex. the insulin gene) can be removed from the cut sequences

3) other restriction enzymes can cut PLASMIDS (circular DNA in bacteria; acts as a vector--carrier of DNA) or DNA strands in another organism

4) then certain enzymes can "paste" the genes you want into the plasmid or other organism

5) the DNA can be reinserted and now contains the recombinant DNA, which will produce the polypeptide it codes for!

 

Molecular Genetics
watch this clip to see the basics of genetic engineering, a.k.a. gene splicing
check out some of the ways that genetic engineering may be applied--can you say, "SPIDER GOATS"?
principals of gel electrophoresis, as used by forensics labs; see the links below for detailed demostrations
click on the 'Transgenic Manipulation' animation to see how to use biotechnology to get a better crop; used in intro to genetic engineering classes
another stand-out interactive animation from the University of Utah--a MUST SEE for gel electrophoresis
take a look at some of the genetically modified foods that are out there; also can click to various viewpoints about these foods; a great discussion topic for kids and parents!
made for the Regents biology students, this goes over with animations the two key lab procedures featured in the 'Botana' lab
a simple explanation and animation of how gel electrophoresis (featured in the 'Botana' lab) works
Check your knowledge on genetic engineering.

VIII. POPULATION GENETICS

* the study of factors which affect gene frequencies (how much a gene is present in a populations) in sexually reproducing organisms

population: all the members of a given species in a given location

gene pool: the SUM TOTAL of all inheritable genes in a population

gene frequency: the percentage of each allele for a particular trait in a population

THE HARDY-WEINBERG PRINCIPLE

the gene pool of a population stays stable (relatively unchanged) as long as certain conditions are met

* these conditions are:

1) a large population
2) mating occurs randomly
3) no migrations (organisms leaving)
4) no mutations (changes in the DNA of the organisms)

HOWEVER:
* in nature, these conditions do not hold true, so the gene pool will change over time...

HMMMM...change over time....sounds like

EVOLUTION

to be continued...

Molecular Genetics