Biology Notes for Test #4: Chromosomes, DNA & RNA Structure, DNA Replication, Protein Synthesis
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Biology Notes for Test #4: Chromosomes, DNA & RNA, Protein Synthesis, Gene Regulation, and Mutations
I. Chromosome Structure (Eukaryotic)
Chromatin – A combination of DNA and proteins called histones. The DNA-histone complex is loosely coiled and is not visible with a light microscope. DNA-histone complex is only in chromatin form during interphase of a cell’s life cycle.
Q: What is the benefit of having DNA in Chromatin form? ______
Chromosomes – Tightly, supercoiled DNA-histone complex. After DNA has been replicated (copied) during interphase, the two copied/identical and supercoiled DNA-histone complexes called chromatids are united by a centromere.
Q: What is the benefit of having DNA in Chromosome form? ______
In all sexually reproducing organisms chromosomes occur in pairs (1 from the mother and 1 from the father.) These pairs are called homologous chromosomes. Homologous chromosomes carry directions/alleles for determining the same traits, like eye color but they do not always carry the same version of directions/alleles for the same trait.
Q: What is the benefit of having variation/differences within a species? ______
1 To determine the number of chromosomes a cell has, count the number of centromeres not the number of DNA strands.
Every species/organism has a characteristic # of chromosomes in each cell.
Q: Does the number of chromosomes determine how complex the organism is? ______
Organism – Kingdom Body/Somatic Cell (2n) Sex Cell/Gamete/Eggs & Sperm (n) All Bacteria 1 0 Yeast – Fungi 32 16 Bread mold – Fungi 8 4 Potato – Plant 48 24 Tobacco – Plant 48 24 Corn – Plant 20 10 Adder’s Tongue Fern – Plant 1,262 631 Chicken 78 39 Dog 78 39 Human 46 23 Chimpanzee 48 24
Cell Types and their Chromosome Number
Cell type w/examples Cell type alternate names Sets of chromosomes per Naming sets of chromosomes cell Body Cells kidney, bone, liver, muscle or
Sex Cells * eggs, sperm * or *
Q: Are there homologous chromosomes in sperm and egg cells? ______Q: Skin and spleen cells? ______
Karyotype – Picture of chromosomes taken in metaphase that have been stained, blown up in size and homologues paired up.
Autosomes- ______
Sex Chromosomes- ______
What distinguishes chromosomes:
Size (# of nucleotides)
Centromere location Sex Chromosomes Autosomes
Sex Cells- Staining pattern Somatic Cells-
2 II. DNA History The structure of DNA was solved together by Francis Crick (English) and James Watson (American) in 1953. They used research skills, communication, & model building to make this one of the most important scientific discoveries in history. Watson and Crick used the hard work of the following scientists: a) Alexander Todd to determine the parts of a nucleotide b) Linus Pauling & Jerry Donahue to determine bond types and angles c) Erwin Chargaff to determine base pairing rules. d) Rosalind Franklin & Maurice Wilkens (X-ray crystallography to determine general position of nucleotides and number of DNA strands
III. DNA Function – DNA (DeoxyriboNucleic Acid) holds directions in the form of a four letter code to make RNA (RiboNucleic Acid), which in turn build proteins. Proteins are vital to most of our bodily functions and to our body’s structural needs.
Structure – DNA is a macromolecule made up of smaller molecules or monomers called… ______.
Phosphate
Deoxyribose (5 carbon sugar)
Nitrogen Containing Base (4 kind) (A) Adenine – double ringed Purines (G) Guanine – double ringed
(T) Thymine – single ring Pyrimidines (C) Cytosine – single ring
DNA is a double stranded molecule with a helical/spiraled shape. The deoxyribose sugars are bonded to phosphates along the outside of the molecule and bases toward the inside of the molecule. The 2 strands are then hydrogen bonded to each other via their bases. Adenine always double hydrogen bonds to Thymine and Guanine always triple hydrogen bonds to Cytosine. This bonding of A=T and GC makes the strands exactly opposite or complementary. Complete the bonding and base pairing below. (Strand #1) P P P P P P
S S S S S _____ =
A A C A T - - - - = ______= Hydrogen Bond S S S S S
(Strand #2) P P P P P P
3 Use the space below to draw and color code a portion (2 base pairs or 4 nucleotides) of an unwound DNA molecule.
Adenine light blue Use black for hydrogen bonds (= or ≡).
Guanine dark green Use light green for phosphodiester bonds.
Use brown for glycosidic bonds. Cytosine purple Shade behind the backbone of the molecule with yellow. Thymine orange Circle a nucleotide with a black circle. Phosphate dark blue Circle the purines with a pink circle. Deoxyribose red Sugar Circle the pyrimidines with a gray circle.
4 III. DNA Replication – Occurs during interphase of a cell’s life cycle, DNA replication is making identical copies of chromosomes.
a) Many DNA Helicase enzymes attach themselves to, and cut hydrogen bonds between bases. Why are so many of DNA Helicase enzymes needed?
b) With H-bonds cut, the 2 strands of DNA are now separating. Free-floating nucleotides within the nucleus now attach to their complement nucleotide, AT & GC.
Q: Where do the “free-floating” nucleotides come from to form a new DNA molecule? ______
DNA Polymerases are the enzymes that will help bond the new nucleotides to the old nucleotides (original strand), they also help the new nucleotides to bond to each other.
Why is DNA replication said to be “semi-conservative?
5 Errors in base pairing are rare, about 1 in every billion. These errors in base pairings, thus changing the sequence of DNA is termed mutation. The agents that cause mutations are termed mutagens (cigarette smoke & tar, asbestos, radiation, etc.).
Gene – A specific sequence of DNA nucleotides/bases which codes for the making of specific proteins ( 30,000 in humans).
IV. RNA Structure and Function
Function – Builds proteins.
Structure – RNA is a macromolecule made of small molecule called…______.
Phosphates Ribose Sugars Nitrogen Containing Bases (4) (C) Cytosine – single ring Pyrimidines (U) Uracil – single ring
(A) Adenine – double ringed Purines (G) Guanine – double ringed
RNA is a single stranded molecule with 3 general shapes, thus 3 general functions.
Messenger RNA (mRNA) – A linear/straight RNA molecule that carries a complementary copy of a gene. The complementary copy of a gene (found on DNA) is called the genetic code (found on mRNA). The genetic code is read 3 bases at a time (AUG, GGA, etc.), which are called codons.
Transfer RNA (tRNA) – A folded RNA molecule that is t-shaped. At the top of the tRNA molecule is the site where amino acids (protein monomers) attach. At the bottom of the tRNA molecule is the site where the genetic code is read. The complement sequence, read 3 bases at a time, reads the mRNA(codon) and is called the anticodon (tRNA).
6 Ribosomal RNA (rRNA) – A folded, globular shaped molecule. rRNA and some proteins are the components of a ribosome.
DNA
rRNA tRNA mRNA
Site of protein synthesis Brings instructions indicating which amino acids will be needed
and in which order they will be bonded together Brings amino acids to the ribosome.
Bonding DNA to RNA, and RNA to RNA follow the complementary bonding of DNA to DNA with one exception (U for T). AU, TA, UA, CG, and GC. Use the sequence of DNA to make a complementary copy of RNA.
DNA A G C T T C G A G G C A T T A
RNA
V. Protein Synthesis (Transcription and Translation) – View genetic code on page 6 and protein synthesis pictures on page 7.
1. Transcription – Process of making all 3 forms of RNA. RNA shape, thus its function, is determined by it base sequence.
The three jobs of RNA polymerase 1. The enzyme RNA Polymerase attaches itself to the hydrogen bonds of a DNA molecule at the beginning of a gene. It then breaks the hydrogen bonds opening the DNA molecule and exposing the bases of a gene.
2. RNA Polymerases then help to form hydrogen bonds between a strand of DNA and free-floating RNA nucleotides. * Remember: bonding is complementary A , T , G , C . There is no Thymine in RNA, Uracil is substituted.
7 3. RNA Polymerases then help to make sugar to phosphate bonds between newly formed RNA nucleotides.
After copying the gene, RNA detaches itself from the DNA molecule and the split strands of DNA now reattach.
After RNA detaches from the DNA molecule it must be modified/changed to become functional/ usable. Enzymes remove portions of the RNA molecule before it is structurally the correct size and shape. The portions of RNA that are transcribed but not translated are called introns (stays in the nucleus) and the portions of RNA that are transcribed and translated (exit the nucleus) are called exons.
2. Translation – The process of RNA making proteins from the encoded directions received from DNA (genes).
After mRNA is made it travels through the nuclear membrane to a ribosome located in the cytoplasm and on rough ER’s.
Once the mRNA reaches a ribosome the 1st codon (______) will be read (AUG is always the 1st codon that is read).
A codon codes for a specific amino acid or gene terminator, a codon may only code for 1 amino acid.
There is redundancy in the code, meaning that more than one codon can code for the same amino acid.
Why do you think that scientists guessed that the genetic code was read 3 bases at a time?
Because AUG is the first codon read while making a protein, then the 1st amino acid brought to the ribosome by tRNA is… ______
What is the anticodon (______) on the tRNA that will carry the 1st amino acid?
After methionine is brought to the ribosome the next codon is read. Upon reading the next codon, a tRNA will bring the next amino acid which is floating in the cytoplasm near the ribosome.
After the 1st two tRNA’s are attached to the mRNA, a peptide bond will form between their amino acids.
After the peptide bond is made between the 1st two amino acids, the 1st tRNA will drop off and seek another methionine.
The ribosome will continue to build a protein in this manner until it reaches a stop or terminator codon, signaling the end of the polypeptide/protein. After reaching a stop codon the protein will be released.
8 What happens to the protein now?
a) b) c)
AA-AA-AA-AA-AA-AA-AA-AA-AA-AA-AA-AA-AA-AA-AA- AA-AA-AA-AA-AA-AA-AA = Polypeptide AA-AA-AA-AA-AA-AA-AA-AA AA-AA-AA-AA-AA-AA-AA-AA= Protein
AA= Amino Acid - = Peptide Bond
The sequence of ______determines the sequence of ______, which determines the sequence of ______.
The # and sequence of ______determines the size and shape of a ______.
Complete the following table for the DNA and mRNA sequences, the anticodons, and their amino acids. Use the genetic code of life (below) to help you answer these questions.
DNA TTC
mRNA (codon) UAG
tRNA (anticodon) CAG
Amino Acid methionine
9 Central Dogma of Biological Sciences
DNA makes RNA makes PROTEINS determines TRAITS ______(process) (process)
______(process) ______
VI. Mutations - Any change in the sequence and/or amount of DNA that a cell possesses.
Somatic Cell Mutations ______
Germ/Sex Cell Mutations – ______
Types of Mutations: Normal Codon Sequence (top line)
1. Gene or Point Mutatations – Mutations that only affect one gene. THE CAT ATE THE RAT
a) Addition or Duplication – ______THE CAT ATE THE THE
b) Subtraction or Deletion – ______THE ATE THE RAT
c) Substitution or Missense – ______THE COT ATE THE RAT
2. Chromosomal Mutations – Mutations that affect many genes on one or more chromosomes.
a) Deletion- ______
b) Duplication- ______
c) Inversion– ______
d) Translocation– ______
e) Nondisjunction – ______
10 Exam #4 Review Sheet
1. Describe the differences between chromatin, nucleosomes, and chromosomes. Be able to identify and define the parts of a chromosome. Sister chromatids – Centromere –
2. What are homologous chromosomes?
3. How many sets of chromosomes are in human body cells? Sex cells?
4. What are the other names for sex cells? Body cells? Give some examples of each. Sex Cells – Body Cells -
5. What is a karyotype?
6. What is the monomer of DNA? What is the monomer of RNA?
7. Why is DNA replication considered semi-conservative?
8. Describe the roles of the following enzymes: DNA Helicase – DNA Polymerase – Ligase
9. How did the following scientists contribute to discovering the structure of DNA? a. Watson and Crick- b. Franklin and Wilkens- c. Chargaff- d. Todd- e. Pauling and Donahue
10. Where do the free-floating nucleotides for DNA Replication and Protein Synthesis come from?
11. Define gene.
12. Name 4 specific physical differences between DNA and RNA a. b. c. d.
13. Describe all three types of RNA (function and shape). mRNA- rRNA- tRNA-
14. What is a codon? What is an anticodon?
15. What is the end result of transcription? 16. What are the functions of RNA Polymerases? * * *
17. What is the end result of translation?
18. The first codon on mRNA to reach the protein is always ______. It codes for the amino acid ______.
11 19. What causes a protein to be released from the ribosome? 20. What happens to the protein after it is released? a. b. c.
21. What is the name of the bonds that link amino acids together? ______
22. The ______& ______of amino acids determines the ______& ______of a ______.
Short Answer: 23. Why is correct DNA Replication important to protein synthesis and cell reproduction?
24. Draw & label an unwound DNA molecule. Show the molecule with 2 complimentary base pairs. Use page 4 of your notes.
25. Using the DNA nucleotides, determine the sequence of the following:
DNA mRNA (codon) tRNA (anticodon) Amino Acids AAA TGA CGC GCA ACG TTC
26. Explain why DNA replication is called “semi-conservative.” Use complete sentences (pictures may also be helpful).
27. List 2 specific, physical differences between DNA and RNA. (4 points)
28. What may happen to a protein if it is built incorrectly (ie. it has the wrong shape and/or size)?
A change in which base would have the least impact on producing the correct protein?
Makes Makes Determine 29. * ______*______*______*______
*______* ______(process) (process)
*______(process)
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