Biology for nonmajors college course Lumen Learning

1. Genes and Proteins

2. Genetic Role and Structure of DNA
• Hershey and Chase experiments
– Showed that viruses inject their DNA into bacteria and
direct bacteria to replicate it for them
• DNA not protein is genetic material
• DNA
– Double helix
– Made of EQUAL amounts of nucleotides: Adenine,
Guanine, Cytosine, Thymine
– Each part of helix is complementary to other, run in
opposite directions
– 3 prime and 5 prime ends

3. Genetic Role and Structure of DNA
• Hershey and Chase experiments and Rosalind
Franklin
– Showed that viruses inject their DNA into bacteria and
direct bacteria to replicate it for them
• DNA not protein is genetic material
Alfred Hershey Alfred Hershey

4. The Structure of DNA (review)
DNA has (a) a double helix structure and (b) phosphodiester bonds. The (c) major and minor
grooves are binding sites for DNA binding proteins during processes such as transcription (the
copying of RNA from DNA) and replication.

5. Base Pairing

6. Double Helix
Structure

7. DNA vs. RNA
• Same basic structure
• Instead of thymine use uracil to pair with adenine
• Single helix
• Helps code for and make proteins
• Types of RNA
– Messenger RNA (mRNA) – carries info. For a specific
protein. Segment is codon
– Ribosomal RNA (rRNA) – combines with proteins to
form ribosome
– Transfer RNA (tRNA) – connectors to bind an mRNA
codon to a specific RNA

8. DNA vs. RNA
DNA encodes the
genetic instructions
used in
development and
function; transfers
to daughter cells
RNA plays an active
role within cells by
catalyzing biological
reactions,
controlling gene
expression, or
sensing and
communicating
responses to
cellular signals

9. The Genetic Code
• Genome – All the genetic material in cells
– All different sizes depending on complexity of
organisms
• Chromosome – Package of DNA and associated
proteins
– You have 23 pairs or 46 total chromosomes
• Gene – sequence of DNA on a chromosome that
codes for a specific protein or RNA molecule

10. Protein Synthesis
• Transcription – Copying a gene’s DNA to a
complementary RNA molecule, occurs in
nucleus
• Translation – Copying translating an mRNA
strand into the language of amino acids

11. Transcription and Translation
Transcription occurs within the nucleus; translation occurs
outside (still within the cell)

12. Transcription
• Transcription – Copying a gene’s DNA to a
complementary RNA molecule, occurs in nucleus
– Just copying the “words”
• Occurs in 3 Steps
– Initiation – Enzymes unzip DNA double helix, RNA
polymerase binds to promoter
• Promoter – DNA sequence at the beginning of a gene
– Elongation – RNA polymerase, adds nucleotides from
3’ to 5’ end making RNA molecule
– Termination – RNA polymerase gets to termination
sequence at end of gene, separates and releases new
RNA molecule

13. Transcription

14. Preparation for Translation
• Bacteria and archaea begin translation as RNA
molecule is being transcribed
• Eukaryotic cells – mRNA can’t cross nuclear
membrane
– Add nucleotide cap to end of 5’ end of mRNA
– Add 100-200 adenines – “poly a-tail”
– Helps ribosomes attach to 5’ end of mRNA
– Helps prevent degradation of mRNA
– Introns removed from RNA, exons spliced together

15. The mRNA then leaves the nucleus of the cell; ribosomes translate from mRNA.

16. Translation
• Translate DNA/RNA language into a amino
acid language to make protein
• Uses
– mRNA – carries codon information
– tRNA – binds to mRNA and amino acid
– Ribosome – anchors mRNA
• Functional Unit = Codon – 3 base pair “word”
that coincides with an amino acid
– Genetic Code

17. Large subunit
• 5,080 RNA bases
• ~49 proteins
Small subunit
• 1,900 RNA bases
• ~33 proteins
Small subunit
Large subunit
Ribosome

18. tRNA
Tertiary structure of tRNA.
CCA tail in yellow, Acceptor
stem in purple, Variable loop
in orange, D arm in red,
Anticodon arm in blue with
Anticodon in black, T arm in
green.

19. tRNA and the ribosome combined

20. Triplet Codon

21. Translation
• Occurs in 3 Steps
– Initiation – at 5’ end “start” codon (AUG) codes for
methionine, calls large subunit, start polypeptide
– Elongation – tRNA brings 2nd amino acid,
covalently bonds with 1st amino acid, release 1st
tRNA, get another tRNA and so on to make poly
peptide chain
– Termination – “Stop” codon (UGA, UAG, or UAA).
NO amino acid corresponds to “stop”, release
factors, release last tRNA, ribosomal units
separate, polypeptide chain released

22. Steps in Translation

23. Steps in
Translation

24. Polypeptide to Protein
• Polypeptide chain is NOT a protein
• Chain folds in cytoplasm to get 3-D structure
• Errors can occur
– Wrong amino acid sequence “messes” up folding
• Cystic fibrosis
– Error in folding with correct sequence
• Alzheimer Disease – incorrect folding of amyloid, forms
mass in brain
– Error in joining polypeptide chains
• Misfire in types or how joined. Hemoglobin

25. How Do Prokaryotic Cells Express
Proteins?
• Operons

26. How Do Prokaryotic Cells Express
Proteins?
• Operons
– Used by bacteria
– Group of genes plus promoter and
operator/repressor
• Operator – DNA sequence between promoter and
protein encoding region
• Repressor – Protein that binds to operator to inhibit
transcription

27. How Do Prokaryotic
Cells Express Proteins?
• Lac Operons: lactose turns
off the repressor

28. How Do Prokaryotic Cells Express
Proteins?
• TRP Operon : presence of TRP = active repressor

29. How Do Eukaryotic Cells Express
Proteins?
• All cells in an organism contain identical DNA
sequences.
– i.e. cloning experiments
on plants

30. How Do Eukaryotic Cells Express
Proteins?
• All cells in an organism contain identical DNA
sequences.
– i.e. cloning experiments on animals

31. How Do Eukaryotic Cells Express
Proteins?
• Transcription Factors
– Eukaryotic Cells
– Bind to DNA at different sequences to control
transcription
– Can bind to promoter or enhancer
– Respond to external stimuli to signal gene to “turn on”
• Signaling molecule binds to outside of cell, triggering
reactions inside
– Defects can cause disease or be used as drugs
• Cancer
• RU486

32. How Do Eukaryotic Cells Express
Proteins?

33. How Do Eukaryotic Cells Express Proteins?
• DNA Availability
– If DNA not “unwound” from double helix, cannot do
transcription
• Molecules bind to DNA and either not allow to unwind or wind it
even tighter

34. How Do Cells Express Proteins?
• RNA Processing
– Removal of introns to change what proteins are
coded for

35. How Do Eukaryotic Cells Express
Proteins?
• Methylation of certain portions of DNA can
deactivate those genes
• X-inactivation
The coloration of tortoiseshell and
calico cats is a visible manifestation
of X-inactivation. The black and
orange alleles of a fur coloration
gene reside on the X chromosome.
For any given patch of fur, the
inactivation of an X chromosome
that carries one gene results in the
fur color of the other, active gene.

36. Mutations
• Mutation – Change in cell’s DNA sequence
• Not always harmful, can lead to genetic variability
• Point Mutation – changes 1 or a few base pairs in
a gene
– Substitution – replacement of 1 DNA base pair with
another
• Silent – mutation codes for same protein
• Missense – mutation codes for different amino acid,
changing proteins shape (ex. Sickle cell anemia)
• Nonsense – mutation codes for “stop” codon instead of
amino acid – makes shorter peptide chain

37. Mutations: Substitution

38. Missense

39. Mutations
• Base Insertions and Deletions
– 1 or more nucleotides are added or subtracted from
gene
• Frameshift Mutation – adds or deleted nucleotides in any
number other than multiple of 3
– Disrupts codon reading, alters amino acid sequence
• Expanding Repeats
– Number of a 2 or 4 nucleotide sequence increases
over several generations
• Symptoms get more and more severe
• Huntington’s Disease – makes extra glutamines, makes
fibrous clumps in brain

40. Mutations: Deletions

41. Mutations: Deletions

42. How are these Mutations Produced?
• Unmatched base pairs can
possibly lead to changes in
the DNA structure

43. How are these Mutations Produced?
• Unmatched base pairs can possibly lead to
changes in the DNA structure
Wild-Type Sequence
DNA CTG ACT CCT GAG GAG AAG TCT
Protein Leu Thr Pro Glu Glu Lys Ser
Amino Acid
Position
3 4 5 6 7 8 9
Sickle Cell Sequence
DNA CTG ACT CCT GTG GAG AAG TCT

44. Mutations
• Causes
– Spontaneous – DNA replication error
– Mutagens – external agent that induces mutations
• UV Radiation, x-rays, chemical weapons, nuclear energy,
tobacco
– During Meiosis
– Transposons – jumping pieces of DNA
• Types
– Germline – occurs in cells that give rise to sperms and
eggs
• Things that run in families
– Somatic – occurs in non-sex cells
• DOES NOT get passed on