BME205

Central Dogma of Biology

DNA —> mRNA —> Amino Acids

What is the process of turning DNA into mRNA?

Transcription

What is the process of turning mRNA to chains of amino acids?

Translation

Efferent Neural signal

Brain to cells

Afferent Neural signal

Receptors to brain

Homeostasis

• A steady state maintained by the body through various processes

Positive Feedback loop

• Rare in the human body

• Labour contractions

Explain process of thermoregulation in terms of control systems (Draw if possible)

1. Stimulus — change in environment

2. Receptors — thermoreceptors in skin detect change

3. Hypothalamus/Thermoregulatory centre — Compares temperature/condition to typical range, sends inter neural signal

4. Eccrine glands, blood vessel, arrestor pili muscles — adjust control variables, sweating, vasodilation, goosebumps

5. Receptors — Remeasure temperature

What happens in neural circuit during negative feedback?

• By ‘Error Dectector’

• Takes input by receptors and subtracts it from acceptable range

• Actions taken to reduce error

What control variables are affected when the stimulus is being too hot?

• Eccrine glands produce more sweat

• Vasodilation: to release more heat

What is a stimulus in terms of homeostasis?

• Change in variable being regulated

Parts of DNA from smallest to largest

• Nucleobase

• Nucleoside

• Nucleotide

• DNA helix

• Histones

• Nucleosomes

• Chromatin

• Chromosome

Histone

Protein that DNA wraps around to be more condensed

What type of gene expressions are there?

1. Tissue specific

2. Inducible

Tissue-specific gene expression (example from Cytosis included)

• Specialized cells only express certain genes and only develop into those specialized cells (bone cells make bone cells) despite having entire genetic code

• In Cytosis would correspond to only making certain hormones

Inducible gene-expression

• Controlled activation of gene in response to specific stimuli —> Vitamin D allows helpful genes to be expressed in osteoblasts

• In Cytosine means that specific protein receptors would be generated

Template strand of DNA

• read in 3’ - 5’ direction during transcription

Coding Strand of DNA

• In 5’ - 3’ direction

• Can be referred to as DNA code

• pre-mRNA is this but with T swapped for U

DNA base pairings?

• A and T

• G and C

What enzyme is used in DNA transcription?

• RNA polymerase

What is needed to start transcription?

1. Distal control elements

2. Proximal control elements

3. TATA box

4. Open reading frame

5. Poly(a) —> AAUAA (termination process begins here)

6. Proximal control

7. Distal control elements

This is on coding strand

Proteins

• Polypeptide chains that holds upon itself due to chemical interactions

Direction of translation

• 5’ - 3’ direction

Elements involved in translation

• tRNA

• Ribosome

Purpose of tRNA

• transfer RNA: have anticodons and bring corresponding protein based on RNA

• Has a wobble position

  • fewer anticodons needed than codons that make proteins

Process of translation

1. Initiation: small ribosome unit attaches to mRNA, begins at start codon (makes methionine)

2. Elongation: Ribosome is assembled, allowing tRNAs to enter and leave, making polypeptide chain longer

3. Termination: Hits stop codon (no protein added) and ribosome breaks apart

Where are ribosomes?

• Endoplasmic reticulum

• Freely floating in cytoplasm

How is energy attained from ATP?

• Hydrolysis: breaking of chemical bond via water

• Faster version involves ATPase to quicken reaction

What is the current model of the cell membrane?

• Fluid mosaic model

• The membrane is primarily made of phospholipids with various channels and proteins to allow various molecules in and out of the cell

What molecules can easily get past phospholipid bilayer?

• Small

• Non-polar/uncharged

Types of membrane transport

• Unassisted membrane transport/simple diffusion

• Facilitated diffusion

• Active transport

• Secondary active transport

Facilitated diffusion

• Done via channel or carrier proteins

• Driving force is gradients (concentration/electrical)

Difference between channel and carrier protein

• Carrier protein has a limit to the rate of intake/output in response to increasing gradients because the protein changes shape in response to a molecule and only allow a certain number in at a time

• Channel proteins essentially allow simple diffusion

Active transport

• May be against concentration gradient

• REQUIRE ATP

• Example: Sodium/Potassium pumps/ATPase

Secondary Active transport

• ATP not used to directly move particle

Resting Membrane Potential

• Voltage/charge diff of a cell at rest

• -70 mV

• Like a weighted average of all ions in cytoplasm

Equilibrium Potential

• The voltage needed for a specific ion to be in dynamic equilibrium (not diffuse in/out)

Difference between ribose and deoxyribose

• deoxyribose is missing an -OH on the 2’ carbon

How is the DNA backbone connected?

• Phosphate group is connected to the 3’ and 5’ carbon via an ester bond (oxygen bonded to the carbon)

What base pairing is harder to break apart?

• G and C as there are 3 hydrogen bonds between them (A and T only have 2)

How many canonical bases are there?

• 5

Describe how a Na+/K+ pump works

Na⁺/K⁺ Pump (Na⁺/K⁺-ATPase):

• Transport protein in the cell membrane

• Uses ATP → active transport

• Moves ions against their concentration gradients

Steps:

1. 3 Na⁺ bind to the pump on the inside of the cell

2. ATP is hydrolyzed → pump becomes phosphorylated

3. Phosphorylation causes a shape change

4. 3 Na⁺ released to the outside of the cell

5. 2 K⁺ bind to the pump on the outside

6. Phosphate group is released

7. Pump returns to original shape

8. 2 K⁺ released into the cell

Net effect:

• 3 Na⁺ out, 2 K⁺ in per ATP

• Helps maintain resting membrane potential

• Maintains ion gradients and cell volume

Process of transcription

• Initiation:
  Transcription factors bind first to the promoter. These factors recruit and correctly position RNA polymerase II, forming the transcription initiation complex. DNA unwinds at the start site.

• Elongation
  RNA polymerase II moves along the template strand (3′ → 5′) and synthesizes RNA 5′ → 3′ by adding complementary RNA nucleotides. Most transcription factors dissociate after initiation.

• Termination
  RNA polymerase encounters termination signals, releasing the RNA transcript and detaching from the DNA.

Which technique can be used to measure resting membrane potential?

Patch-clamp technique