Genes And Gene Expression

Front 1

Describe the structures of DNA and RNA and explain how these molecules encode the sequence and structures of proteins.

Back 1

*DNA and RNA are nucleotides composed of a sugar (either ribose or deoxyribose), phosphate and a nitrogenous base (RNA: AGCU; DNA:AGCT).
*Ester bonds between phosphate groups mediate polymerization.
*The information in DNA is transcribed to RNA which is then translated into discrete amino acids for every three nucleotides.

Front 2

Explain how DNA is packaged into chromatin, and describe the significance of heterochromatin vs. euchromatin with respect to gene expression.

Back 2

*Genomic DNA wraps around octomers of histones, forming nucleosomes. Other accessory proteins bind DNA but do not contribute to chromosomal structure
*Euchromatin is indicative of areas of the genome that are highly expressed. The chromatin is decondensed, allowing transcriptional machinery and factors to localize easily to genes. It is stained lighter than heterochromatin.
*Heterochromatin is highly condensed and represents silenced areas of the genome. Highly heterochromatic chromatic is indicative of a terminally differentiated cell. (appears darker under microscopic observation because it stains deeper).

Front 3

Define the term genome.

Back 3

The entire nuclear DNA content of a cell or an organism.

Front 4

Describes the steps in transcription of a gene and processing of the primary transcript.

Back 4

a.
5'--------------------------------------------------------------------3'

3'--------------------------------------------------------------------5' Promoter | Coding Region | Terminator

-Above is a general schematic of a gene. The promoter is the loading dock area for the RNA Polymerase. The helix begins to unwind here.
-The RNA polymerase begins transcribing the 3'-5 strand by creating a complementary mRNA
strand from 5'-3'.
-Termination of the transcript is signaled by the terminator sequence on the DNA template.
-Certain regulatory sequences can be present to increase (express) or decrease (silence) the likelihood of RNA polymerase transcribing the gene.

b.
5'-------------------------------------3'
*The above primary mRNA transcript has 5'cap added to the 5' end of mRNA to protect from exonucleases (chews nucleotides from ends).
*A string of up to 250 Adenines are added to the 3' end of the transcript to form the poly (A) tail

to also protect from exonuclease activity.
*RNA splicing occurs to remove the introns (non-protein coding segments). snRNP's bind and recognize certain splice signals to create a spliceosome. This macromolecular machinery catalyzes the removal of introns. Now the transcript is ready to leave the nucleus to be translated.

Translation is production of protein from mRNA involving ribosomes and rRNA molecules that bring amino acids in discrete intervals of 3 nucleotides to the ribosome-mRNA junction.

Front 5

Describe the organization and properties of the genetic code.

Back 5

a. The transcript is read in discrete intervals of 3 nucleotides (codons) that are translated into a single amino acid. The ribosome does not have to start at the first nucleotide of the mRNA transcript (usually never does either). This creates 3 possible reading frames that could potentially create 3 very different proteins.
5-CCCtttGGGaaaTTT-3'
5'ccCTTtggGAAattT-3'
5'-cCCTttgGGAaatTT-3'

Ser-Met-Gly-Leu---Phe---Met

UCG AUG GGU CUU UUU AUG AGCTACCCAGAAAAATAC

Front 6

Describe the process by which mRNA is translated into a protein.

Back 6

*mRNA functions to transfer to the genetic information from the nucleus to the ribosomes in the cytoplasm.
*Each codon found on the mRNA has a complement tRNA whose anticodon is complementary (complicated by wobble). The specific tRNA has an amino acid covalenty attached to it via aminoacyl-tRNA synthetases.
*The ribosome (made of ribosomal RNA and protein) translates the nucleotide seuquence into
an amino acid sequence by having tRNA has an adaptor that bring each amino acid in the correct sequence to the end of the growing polypeptide chain.

Front 7

Describe the roles of mRNA, tRNA, aminoacyl-tRNA synthetases, rRNA and ribosomes in translation.

Back 7

mRNA: encodes protein's primary structure
tRNA: decode mRNA codons and position corresponding, attached amino acid in place for peptide bond formation
amino acid tRNA synthetases: charge tRNA with correct amino acids
rRNA: makes up ribosomal protein
ribosomes: brings mRNA and tRNA together in the correct fashion/line-up and catalyzes peptide

bond formation

Front 8

Diagram a gene, including coding regions, noncoding regulatory regions, introns, exons, and splicing sequences.

Back 8

draw it baby

Front 9

describe simple squamous epithelial cells:
- shape
- location
- functions

Back 9

- flat, irregular shape
- blood vessel / organ mesothelium
- transport of nutrient; adhesion / permeability / barrier / organ mesothelium

Front 10

describe stratified squamous epithelial cells:
- shape
- location
- functions

Back 10

- flat, irregular shape
- skin, espohagus
- protection / permeability barrier

Front 11

describe simple cubodial epithelial cells:
- shape
- location
- functions

Back 11

- cell height = width
- kidney tubules, thyroid gland
- secretion; ion transport

Front 12

describe stratified cubodial epithelial cells:
- shape
- location
- functions

Back 12

- cell height = width
- sweat glands
- protection; secretion

Front 13

describe simple columnar epithelial cells:
- shape
- location
- functions

Back 13

- cell height > width
- intestinal lining, goblet cell
- absorption; secretion

Front 14

describe pseudostratified columnar epithelial cells:
- shape
- location
- functions

Back 14

- cell height > width
- trachea airways
- protection; cilia move mucus

Front 15

2. Explain the concept of a polarized cell and its key features. Name specialized structures of the apical, basal, and lateral surfaces

Back 15

Polarized cell = apical surface is molecularly & functionally different than basal surface (i.e. different proteins on each side)

Apical
>> Function - secretion, absorption, protection, pump
>> Features - microvilli, cilia, endocytosis

Basal:
>> Function - ion pump, synthesis of basement membrane, transport of absorbed substances
>> Features - rests on basement membrane and faces connective tissue, infolding of basement membrane

Lateral:
>> Function: contact and form structions with nearby cells (ie: form seals, structural support)
>> Feature - cell junctions

Front 16

Describe tight junctions found in epithelia
- formal name
- location
- function
- proteins involved
- appearance

Back 16

Formal name: occluding zonule

Location:
1. uppermost componenet of junctional complex
2. at the apex of the cell
3. joins two neighboring membranes tightly together

Functions: controls permeability
1. prevent diffusion between the apical and basolateral surfaces of the epithelial cell
2. prevent paracellular leakage of EC substances between the cells or across the apithelium
- therefore: can block passage of ions, water, and molecules of all sizes from passing between the cells

Proteins involved: claudins, occludins

Appearance: cells appear fused together, eliminating the intracellular space

Front 17

Describe adherens junction found in epithelia
- formal name
- location
- function
- proteins involved
- appearance?

Back 17

Formal name: adhering zonule

Location:
1. continous ring around the apex of the cell
2. generally below tight junctions

Functions:
1. cadherin domain on one cell binds to identical cadherin domain of another cell, producing a strong bond
2. sorting function, useful in the organization of organs

Proteins involved: cadherin (binding to other cells), catenin (link to actin cytoskeleton within cell)

Front 18

Describe desmosomes found in epithelia
- formal name
- location
- function
- proteins involved
- appearance

Back 18

Formal name: desmosomes

Location:
1. not a continuous ring around the cell
2. can be scattered in different locations

Functions:
1. provide mechanical strength to epithelial sheets
2. resist shearing force

Proteins involved: cadherin (form the bond between desmosomes in adjoining cells), connect to intermediate filament cytoskeleton

Appearance: spot welds

Front 19

Describe gap junctions found in epithelia
- formal name
- location
- function
- proteins involved
- appearance

Back 19

Formal name: gap junctions

Location: not limited to epithelial tissues. Na+ transport between cardiac muscle cells take place via gap junctions

Functions:
1. allow small molecules to pass between cytoplasm of two cells
2. synchronization

Proteins involved: connexins (6 protein subunits that surround a central aqueous canal)

Appearance: plasma membrane of 2 cells are adjacent but not fused

Front 20

4. Explain the molecular and cellular mechanisms of directional transport of glucose across a polarized cell in the intestinal epithelium

Back 20

Apical surface
1. Na+ / glu symport couples Na+'s movement down its electrochemical gradient to transport glucose INTO cell (secondary active transport)

Basolateral surface
2. Na+ / K+ ATPase uses ATP hydrolysis to pump 3 Na+ out of the cell and 2 K+ into cell
(primary active transport) - serves to maintain secondary active transport on apical surface
3. glucose passively diffuses out of cell and into bloodstream through a passive glucose transporter found only on the basolateral surface

Front 21

5. Describe the polarized release of mucus from a goblet cell in the intestinal epithelium.

Back 21

mucus = slippery, viscous material made up of heavily glycosylated glycoprotein. secreted by GOBLET CELLS

Goblet cells
ł features:
ł well-developed RER — for protein synthesis
ł large golgi complex
ł abundant secretory vesicles @ apex

Release of mucus: mucus is stored in vesicles of goblet cells and release is stimulated by an increase in intracellular Ca2+

Front 22

6. Explain the function of adult epithelial stem cells.

Back 22

adult epithelial stem cells = undifferentiated epithelial cells that give rise to new epithelial cells

ł during mitosis, one daughter cell continues undergoes mitosis while the other becomes differentiated
ł stem cells are needed to keep the # of epithelial cells CONSTANT
ł they give rise to new epithelial cells in response to distress