BSC2010 Ch. 3 Study Guide

plasma membrane, cytoplasm, DNA, ribosomes

all cells contain…

microvilli

increases surface area of the membrane by creating many tiny projections on the cell’s surface, which adds more membrane space w/out significantly increasing the cell’s volume. This extra space allows the cell to absorb more nutrients the cell to absorb more nutrients or exchange materials efficiently—especially in places like the small intestine, where absorption is important

surface area to volume ratio

refers to how much cell membrane SA is available compared to the cell’s internal volume, and as a cell gets larger, its volume increases faster than its SA, making it harder to efficiently move nutrients in and wastes out

no nucleus, nucleoid (DNA region), single circular DNA molecule, peptidoglycan cell wall, may have flagella

key features of prokaryotic cells (bacteria)

peptidoglycan cell wall

rigid layer outside plasma membrane of bacteria that gives the cell its shape and protects it from bursting: made of sugars (long chains) and short amino acid chains that link sugars together

flagella

movement structures that help bacteria swim

cholesterol prevents the membrane from changing too much hen temperature changes

what does “cholesterol buffers fluidity” mean?

glycoproteins

help cells identify, communicate, and stick to each other

fluidity increases when saturation decreases

more fluid bc unsaturated fatty acids have more double bonds, double bonds create kinks in the tails. Kinked tails can’t pack closely together. Looser packing = more movement = more fluid membrane

fluidity increases with shorter fatty acid chains

more fluid bc less SA, less IMFs bt tails, weaker attractions = phospholipids don’t stick together as tightly. Result: the membrane moves more easily so it is more fluid

cholesterol stabilizes at high temperatures by…

fitting bt phospholipid tails, restricting their movement, and reducing how much they slide past each other

selectively permeable

membrane allows some substances through but not others

simple and facilitated diffusion

types of passive transport/diffusion

passive transport

no energy required, moves down concentration gradient

active transport

requires ATP, moves against concentration gradient

simple diffusion

nonpolar molecules, directly through bilayer

facilitated diffusion

polar molecules/ions, requires channels or carriers

Na+/K+ pump

3 Na+ out, 2 K+ in, uses ATP

maintains membrane potential, critical for neurons

Na+/K+ pump function

endocytosis

membrane folds inward and forms a vesicle, requires energy (ATP)

phagocytosis, pinocytosis, receptor-mediated

types of endocytosis

phagocytosis

“cell eating”, used for big, solid materials

pinocytosis

“cell drinking”, used for small dissolved molecules in fluid

receptor-mediated endocytosis

used for specific molecules like cholesterol or hormones

exocytosis

vesicle fuses with the membrane and empties its contents outside, also requires ATP

endosymbiont theory

mitochondria and chloroplasts were once free-living bacteria, engulfed by ancestral eukaryote and became symbiotic

evidence for endosymbiont theory

mitochondria and chloroplasts both contain double membranes, their own DNA, and ribosomes resemble bacteria

ribosomes

responsible for protein synthesis and are found in the cytoplasm (free) or bound to the rough ER

rough ER

helps process and transport of certain proteins, has ribosomes (which make the proteins), protein synthesis

smooth ER

lipid synthesis, detox, calcium storage

Golgi apparatus

modifies, sorts, and packages (mostly proteins in RER and some lipids in SER) into vesicles

vesicles

small membrane-bound sacs inside cells that transport or store substances

lysosomes

digestive enzymes, break down waste

peroxisomes

break down fatty acids, detox hydrogen peroxide

nucleus

contains DNA, nuclear envelope

nucleolus

makes rRNA (ribosomal RNA), assembles ribosomes

mitochondria

ATP production, double membrane, own DNA

DNA

long-term storage of genetic information

RNA

working copy or messenger of that information

chloroplast

photosynthesis, has its own DNA

central vacuole

water storage, turgor pressure

turgor pressure

the water pressure inside plant cells that keeps the plant rigid and standing, the central vacuole fills w/ water and the swollen vacuole pushes the cytoplasm against the cell wall

cell wall

cellulose, structural support

cytoskeleton structures

centrosome, centrioles, microtubules

centrosome and centrioles

centrosome = microtubule organizing center

contains two centrioles, important for cell division

microtubules

maintain structure, from mitotic spindle, aid in transport

nucleosides

a sugar and a base

nucleotides

a nucleoside and one or more phosphate groups

nucleic acids

linear polymers of nucleotides

DNA: stores energy information, can copy itself

RNA: protein synthesis regulating gene expression

purines and pyrimidines

nitrogen containing bases

purines

adenine and guanine, have a double-ring structure

pyrimidines

cytosine, uracil (RNA only), and thymine (DNA only); have a one ring structure

nucleotides

are always added to then 3’ end of a growing DNA or RNA strand

phosphodiester bond

located between a phosphate group and the sugar molecules of 2 nucleotides; the sugar-phosphate backbone of nucleic acids

a phosphodiester bond between the 3’ hydroxyl group (-OH) of the growing DNA strand and the 5’ phosphate of the incoming nucleotide (strand grows 5’ to 3’, the bond itself connect 3’ to 5’)

nucleotides are attached by…

complementary base pairing of DNA

A-T (2 hydrogen bonds)

G-C (3 hydrogen bonds—stronger)

central dogma theory

genetic info. flows from DNA—RNA—protein (transcription, translation)

eukaryotes—nucleus; prokaryotes—cytoplasm

where does transcription take place?

initiation, elongation, termination

steps of transcription

transcription

process of making an RNA copy of a gene in DNA

translation

process of using the mRNA sequence to build a protein

initiation

RNA polymerase binds promoter, DNA unwinds (start)

elongation

RNA polymerase will synthesize mRNA in the 5’ to 3’ direction, POL forms phosphodiester bonds between nucleotides (releases byproduct of pyrophosphate PPi), RNA POL unwinds and rewinds DNA as it reads

termination (bacteria)

POL will stop transcribing at the end of the terminator and the mRNA can be translated w/out further modification

promoter

piece of DNA upstream that indicates where RNA polymerase should bind to start

TATA box

common promoter sequence where transcription factors bind to form the transcription initiation complex, RNA polymerase then binds to this complex and unwinds the DNA strands

bind to the promoter first and help recruit RNA polymerase

in eukaryotes, transcription…

termination (eukaryotes)

RNA is modified after transcription:

• 5’ G cap added

• 3’ poly-A tail added (polyadenylation)

• introns removed (splicing)

• processed mRNA exits the nucleus for translation

true

T/F?: prokaryotes have no nucleus, so the transcription and translation are coupled

false—translation occurs in the ribosomes in the cytoplasm

T/F?: eukaryotes have a nucleus, transcription and translation are separated with transcription happening in the nucleus and translation in the cytoplasm

eukaryotic RNA polymerases

RNA polymerase reads the template strand 3’—5’; RNA is synthesized 5’—3’

RNA Polymerase I

transcribes rRNA genes, genes are concentrated in the nucleolus

RNA Polymerase II

transcription of protein coding genes (mRNA)

RNA Polymerase III

transcribes rRNA, tRNA, + snRNA

peptide bonds

the end carboxyl group of one amino acid will forma bond with the starting amino acid group of another amino acid, this results in a polypeptide chain

tRNA (transfer RNA)

RNA molecule that reads the mRNA sequence and brings the correct amino acid to the ribosome, growing the polypeptide chain

anticodon

3 nucleotide sequence at the base of the tRNA. This sequence is complementary to the mRNA codon, ensuring the proper amino acid is brought to the ribosome

to take genetic code from mRNA and translate it into a polypeptide chain that will fold to create a protein

the goal of translation is?

A site, P site, E site

the 3 functional sites inside the ribosome

A site

the tRNA carrying the correct amino acid enters through this site

P site

the polypeptide chain is held here

E site

the empty tRNA leaves through this site

codon recognition (energy used, GPT —> GDP + P); peptide bond formation (peptidyl transferase); translocation (energy used, GTP —> GDP +P)

elongation happens in 3 steps:

the polypeptide is arranged:

• with the amino acid facing the start of the chain

• the carboxyl group facing the end of the chain (closer to tRNA)

elongation: polypeptide strand

termination (in more detail)

• the ribosome reaches a stop codon

• release factors enter the ribosome through the A site

• this causing the previous tRNA holding the polypeptide chain to release the chain and exit the ribosome

• the entire ribosomal unit dissociates off the mRNA

protein sorting

if a protein was made in a free ribosome in the cytoplasm: cytosol—nucleus, mitochondria, or peroxisomes

if a protein was made in a ribosome on the rough ER: secretion—membrane insertion, lysosomes

proteins made on free ribosomes

amino acid signal sequences with the polypeptide chain determine where it will go

• no signal: remain in cytosol

• if the signal sequence is on the amino terminal end: chloroplast or mitochondria

• if the signal sequence is in the middle of the chain: nucleus

proteins made on the rough ER

• starts during translation process (as the amino acid chain is growing, its creating a specific sequence on the N-terminus (amino group side) of the amino acid chain

• a signal recognition particle binds to this sequence (while the elongation process is still going) and guides the ribosomal mechanism to the RER membrane

• the ribosome is still completing this elongation process, except the polypeptide chain will be feed into the ER membrane (aka ER lumen)

• inside the ER, proteins are folded (they are also checked for quality)

• they are then transferred to the Golgi apparatus and packaged (like envelopes) and sent to their final destination

the chemical properties of the amino acid

the R group of an amino acid determines…

the amino group of one amino acid and the carboxyl group of another

a peptide bond forms between…

accepting incoming aminoacyl-tRNA

the A site of the ribosome is responsible for…

stop codon

translation terminates when the ribosome reaches a…

cytoplasm (free or RER-bound ribosomes)

translation occurs in the…

polypeptide

the product of translation is a…

carry codons that specify amino acids

the role of mRNA during translation is to…

deliver amino acids based on anticodon recognition

the role of tRNA during translation is to…

A—P—E

during elongation, the correct flow of tRNA through the ribosome is…

remain in the cytosol or go to organelles like the nucleus/mitochondria

proteins made on free ribosomes typically…

directs the ribosome to the RER membrane

what is the function of the SRP (signal recognition particle)?

RER—Golgi—secretory vesicle—plasma membrane

which of the following correctly describes the path of a secreted protein?