L7 - What are Proteins?

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Last updated 11:12 PM on 5/23/26
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13 Terms

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<p>polypeptide</p>

polypeptide

= AA joined via peptide bond

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How many protein encoding genes do humans have?

< 21,000

ex. 9,379 in heart cell

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How big is our largest protein?

34,000 AA (Titan - lecture 26)

→ average human protein is 450 AA in size

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Active Genes in cells

  • housekeeping genes = common active genes b/w different cells → make glycolysis enzymes

  • cell specific genes = genes specific to a cell

<ul><li><p>housekeeping genes = common active genes b/w different cells → make glycolysis enzymes</p></li></ul><p></p><ul><li><p>cell specific genes = genes specific to a cell </p></li></ul><p></p>
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<p>Structure of Proteins</p>

Structure of Proteins

primary = AA sequence

secondary

  • b-sheets & alpha-helix

tertiary

  • disulfide bonds are part of tertiary structure

quaternary

<p>primary = AA sequence</p><p>secondary</p><ul><li><p>b-sheets &amp; alpha-helix</p></li></ul><p>tertiary</p><ul><li><p>disulfide bonds are part of tertiary structure</p></li></ul><p>quaternary </p>
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8 general functions of proteins

  1. enzymes = catalyze covalent bond breakage/formation

  2. structural proteins = provide mechanical support to cells & tissues

  3. transport proteins = carry small molecules/ions

  4. motor proteins = generate movement in cells & tissues

  5. storage proteins = store AA’s or ions

  6. signal proteins = carry extracellular signals b/w cells

  7. receptor proteins = detect signals & transmit them to the cells response machinery

  8. gene regulatory proteins = bind to DNA to to turn on/off genes

  1. special purpose proteins

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<p>4 Ways to depict proteins</p>

4 Ways to depict proteins

  1. primary structure only

  2. space-filling

  3. wire model

  4. ribbon model - useful for tertiary & secondary structure

<ol><li><p>primary structure only </p></li><li><p>space-filling </p></li><li><p>wire model</p></li><li><p>ribbon model - useful for tertiary &amp; secondary structure</p></li></ol><p></p>
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<p>3 main shapes of proteins</p>

3 main shapes of proteins

  1. Globular = compact + most are soluble

  2. membrane = cylindrical + most have PHOBIC band around middle

  3. Fibrous = long & thin + most are bonded into huge filaments

<ol><li><p>Globular = compact + most are soluble </p></li><li><p>membrane = cylindrical + most have PHOBIC band around middle</p></li><li><p>Fibrous = long &amp; thin + most are bonded into huge filaments</p></li></ol><p></p>
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<p>a protein domain</p>

a protein domain

= portion of proteins that can fold, function, and evolve INDEPENDENTLY of each other

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<p>How can a cell make some proteins, but NOT make others?</p>

How can a cell make some proteins, but NOT make others?

  • most regulation of proteins synthesis occurs at the level of RNA synthesis initiation → requires proteins that can bind to genes

  • genes are regulated by Transcription Factor proteins (2 types) → that increase or decreases gene expression

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<p>Transciption Factor proteins </p>

Transciption Factor proteins

= regulate gene expression

  • (+) TF = recruit RNA pols → get increased gene expression

  • (-) TF = block promoter of gene → get decreased gene expression

<p>= regulate gene expression </p><ul><li><p>(+) TF = recruit RNA pols → get increased gene expression</p></li><li><p>(-) TF = block promoter of gene → get decreased gene expression</p></li></ul><p></p>
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How can a cell control the activity of proteins?

  • regulation by phosphates: kinase adds p, phosphatase removes p

→ results in a shape change ( P attached w a covalent bond + turned ON)

  • regulation by nucleotides

ex. GDP (off) → GTP (on)

  • regulation by activator or inhibitor proteins

<ul><li><p>regulation by phosphates: kinase adds p, phosphatase removes p</p></li></ul><p>→ results in a shape change ( P attached w a covalent bond + turned ON)</p><p></p><ul><li><p>regulation by nucleotides </p></li></ul><p>ex. GDP (off) → GTP (on)</p><p></p><ul><li><p>regulation by activator or inhibitor proteins </p></li></ul><p></p>
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<p>What happens to old and unwanted cells?</p>

What happens to old and unwanted cells?

  • recycled into AA by lysosomes (organelles) & proteasome (protein complexes)

NOTE: some proteins are deliberately marked for destruction with small Ubiquitin proteins

<ul><li><p>recycled into AA by lysosomes (organelles) &amp; proteasome (protein complexes)</p></li></ul><p></p><p>NOTE: some proteins are deliberately marked for destruction with small Ubiquitin proteins </p><p></p>