bio exam two objective questions

what is the definition of translation

is the process in which the sequence of bases in mRNA specifies the order in which amino acids are added to polypeptide chains

what are the factors required for translation

mRNA, ribosomes, tRNA molecules, Amino acids, aminoacylt-tRNA syntheses, initiation factors, elongation factors , release factors

what is the structure of the ribosomes?

it is a complex structure of RNA and protein that binds mRNA and controls translation

Ribosomes consit of

a small subunit and a large subunit; th large subunit contains the three tRNA- binding sites

what are the three binding sites for tRNAs

A-site, P-site, E-site

what is the A-site; aminoacyl site

where the incoming charged tRNA enters

what is the P-site; peptide site

holds the tRNA carrying the growing polypeptide

what is the e-site; exit site

where the uncharged tRNA exits the ribosomes

what is a codon

a group of three adjacent nucleotides in mRNA that codes for an amino acid

what is a reading frame

it is the region where the ribosome begins reading the sequence of nucleotides

how are they connected

the ribosome determines the correct reading frame for the codons; AUG is the start codon and corresponds to methionine

what is the difference in prokaryotic and eukaryotic ribosomes

eukaryotic ribosomes are lager than prokaryotic ribosomes

what are the similarities of eukaryotic and prokaryotic ribosomes

they both contain a small and large subunit, their subunit sizes are measure in Svedberg units (S)

what is the structure of tRNA molecules

about 70-90 nucleotides long, they fold into a characteristic self-pairing or cloverleaf structure, folded into a specific three-dimensional structure, they have CCA math their 3’ end, the 3’ OH of the terminal A is the attachment site for an amino acid

what are the key features of tRNA molecules

they carry amino acids to the ribosomes, they contain and anticodon that base pairs with an mRNA codon, it has a CCA sequence at the 3’ end, the amino acid attaches to the 3’-OH of the terminal adenine, each tRNA has its own characteristic structure

what is the fiction of. tRNA synthetase

it connects specific amino acids to specific tRNA molecules

what is tRNA syntheses role in charging tRNAs

a tRNA without an amino acid attached is uncharged but a tRNA with an amino acid attached is charged. Aminoacy-tRNA synthetases attach the correct amino acid to its specific tRNA, these enzymes are very accurate and rarely attach the wrong amino acid

describe the base paring properties between codons and anticodons

this type of pairing is anitparellel - first base of the mRNA codon is at the 5’end then it pairs with the last base of the tRNA anticodon at the 3’ end - base paring determines the specificity of the codon-anticodon interaction

what is the degeneracy of the genetic code

there are 20 amino acids and 64 codons, many amino acids are specified by more that on codon which means the genetic cods is redundant or degenerate

How do you read the codon chart

read the mRNA coding int he 5’→3’ direction and use the three bases of thecodont to locate the corresponding amino acid on the genetic code chart

what is the start codon

AUG= methionine/start codon

what are the stop codons

UAA, UGA, UAG

translation initiation in eukaryotes

intitiation complex forms at the 5’ cap and it scans along the mRNA until it reaches the start codon AUG

translation initiation in prokaryotes

mRNA lacks the 5’ cap so the initiation occurs at an internal sequence called the Shine-Dalgarno sequence

describe the process of translation initiation and the role of initiation factors

1. initiation factors bind to the 5’ cap of the mRNA

2. they recruit the small ribosomal subunit

3. Another initiation factor brings a tRNA charged with methionine

4. the initiation complex moves along the mRNA until it reaches AUG

5. the large ribosomal subunit joins

6. imitation factors are released

7. the next tRNA is ready to enter the A site

describe the process of translation elongation

1. a charged tRNA enters the A-site

2. a peptide bond forms

3. the growing peptide is transferred to the tRNA in the A site

4. the ribosome shifts one codon

5. the uncharged tRNA moves to the E site and exits

6. the peptide-bearing tRNA moves from A→P

7. the A site becomes available for the next charged tRNA

repeating cycle as the polypeptide grows

describe translation termination and the role of release factors

elongation continues until a stop codon is reached such as UAA, UAG, UGA, a release factor protein binds to the A site which causes the bond connecting the polypeptide to the tRNA in the P site to break, releasing the completed polypeptide and creating its carboxyl terminus

what is the structure of an amino acid

it contains an amino group, a carboxyl group, a central alpha carbon, atom hydrogen, an r group/side chain, the r group gives each amino acid its unique chemical and physical properties

how are amino acids classified based on their structure and atomic makeup of their r group

1. how they interact with water- hydrophilic or hydrophobic

2. whether they are basic or acidic

3. whether they are polar or non polar

what are hydrophobic amino acids

they avoid water, they tend to be located in the interior of folded proteins, they are generally non polar

what are hydrophilic amino acids

interact all with water, polar side chains can form hydrogen bonds with water or other molecules, acidic and basic amino acids are strongly polar and hydrophilic, basic amnio acids are positively charged, acidic amino acids are negatively charged

what are the three special amino acids

glycine, proline, cysteine

what is Glycine

its r-group is hydrogen, small and non polar, allows freer rotation around the C-N bond, it increases flexibility of the polypeptide backbone

what is Proline

its r-group is linked cake to the amino group , it restricts rotation around the C-N bond, and it constrains protein folding near proline

what is Cysteine

contains an -SH sulphydryl group, two of them can form s-s disulfide bonds, these bridges can connect different parts of the same protein different proteins

what are the four levels of protein structure

primary structure, secondary structure, tertiary structure, Quaternary structure

what is the primary level?

the sequence of amino acids

secondary structure

interactions between stretches of nearby amino acids, producing structures such as the alpha helix and the beta sheets which are stabilized by hydrogen bonds in the polypeptide bonds

tertiary structure

the overall three dimensional shape of a protein, determined by R-group interactions and the distribution of hydrophobic and hydrophilic side chains

Quaternary structure

multiple protein subunits combine to form a single protein the subunits may be identical or different

what is denaturation

protein becomes unfolded, can occur form chemical treatment o high temperature, secondary and tertiary structures are disrupted, the protein loses its function

what is renaturation

if the optimal conditions are restored the protein can refold and regain its functions

what is the functional role of chaperone proteins

aid in the folding of slow-folding proteins, shield hydrophobic groups to prevent proteins form aggregating, and give a protein time to find its correct 3d shape

what is the structure of a phospholipid

it is amphipathic so it contains a hydrophilic and hydrophobic region they are major types of lipid found int he cell membrane

what structures do phospholipids form with each other in an aqueous environment

large head group+ one hydrophobic tail→ micelles

small head group +two hydrophobic tails→bilayer

what structures do phospholipids form with each other in a test tube

phospholipids spontaneously form enclosed bilayers called liposomes

what is the role of Van Der Waals forcesne

they associate through Van Der Waals forces these weak interactions allow them to move within the plane of the membrane and make the membrane fluid

what is the function fatty acid chain flexibility in the composition of a plasma membrane

these can flex and bend which gives the membrane flexibility which make the membrane dynamic

what is a saturated fatty acid chain

they have no double bonds between neighboring carbon atoms and they can pack tightly

unsaturated fatty acid chains

they have double bonds between neighboring carbon atoms and they do not pack tightly, the strength of their tail interactions depend on the presence or absence of double bonds and the length of the tails

how do saturated fatty acid chains contribute to plasma membrane properties

tighter packing and less membrane fluidity, these are also in a higher concentration ointment the organisms living in warmer clients

how do unsaturated fatty acid chains contribute to plasma membrane properties

less tight packing and greater membrane fluidity

what are the properties of cholesterol

it is component of animal cell membranes, it is amphipathic, it has hydrophilic hydroxyl group, and has a hydrophobic region consisting of four interconnected carbon rings

what is cholesterols effect on membrane fluidity at normal and cooler temperatures - lower temps

it prevents phospholipids form packing tightly and increases membrane fluidity

what is cholesterols effect on membrane fluidity at normal and cooler temperatures -normal cell temperatures

it interacts with fatty acid tails and reduces phospholipid mobility and reduces membrane fluidity

what are the four classes of proteins that associate with the plasma membrane

transporters, anchors, enzymes, receptors

what are transporters

move ions or molecules across the membrane

what are anchors

attach to proteins that maintain cell structure and shape

what are enzymes

catalyze chemical reactions

what are receptors

allow the cell to receive signals form the environment

what are integral membrane proteins

permanently associated with the membrane and they span the lipid bilayer

what are peripheral membrane proteins

temporarily associate with the lipid bilayer or integral membrane proteins, associated through weak non covalent interactions, can be on the internal or external side of the membrane

describe the fluid mosaic model of plasma membranes

the membrane mosaic this because lipids and proteins coexist within them, it is fluid because molecules can move laterally with the membrane

Describe the function of the plasma membrane and its role as a selective barrier

defines the boundary of the cell, separates internal cell contents from the surrounding environment, helps maintain homeostasis, and act as a selective barrier- it allows some molecules to move in and out freely while others move under certain conditions or cannot move across

What is diffusion

molecules move from high→low concentration with passive transport and does not require energy

what is facilitated diffusion

molecules that move through a membrane protein channel or carrier and use passive transport

what is osmosis

the diffusion of water where water moves efficiently through aquaporins

what is primary active transport

moves substances against the concentration gradient, requires energy, ex. sodium/potassium which uses ATP

secondary active transport

uses active transports to create an electrochemical gradient, that gradient drives transport of molecules through a different transporter

describe the effects of osmosis on cells -hypertonic

water leaves the cell which means the cell shrinks

describe the effects of osmosis on cells- isotonic

the cell maintains an appropriate balance of water movement - cells use active transport to help keep intracellular fluid isotonic

describe the effects of osmosis on cells- hypotonic

water enters the cell which means the cells swells and can potentially lyse

what is the function of -plant cell walls

they are rigid structures that surround the plasma membrane and they resist cell expansion when water enters the cell

what is the function of- turgor pressure

force that is exerted by water pressing against the cell wall

does a prokaryote have a nucleus

No it has a nucleoid region

does a eukaryote have a nucleus

Yes

where does transcription take place in a prokaryote

the cytoplasm

where does transcription take place in a eukaryote

nucleus

where does translation take place in both eukaryotes and prokaryotes

Cytoplasm

what are the typical features of an animal cell

they have a plasma membrane which is the boundary of the shell, nucleus contains the DNA, they have endoplasmic reticulum that is involved in portion and lipid synthesis, Golgi apparatus which modifies and sorts proteins and lipids, lysosome that contain enzymes, mitochondria which harnesses energy, and a cytoskeleton which is a protein scaffold that provides structure

what are the typical features of a plant cell

plant cells have many of the same organelles as animal cells but they also have a cell wall which provides additional support, vacuoles that contribute to cell structure by maintaining turgor pressure, chloroplasts convert sunlight energy into chemical energy the cytoplasm consists of everything in the cell except the nucleus; the cytosol is the region outside organelles but inside the plasma membrane

what are the components of the end-membrane system

nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, plasma membrane, vesicles that move between them

what is the nuclear envelope

it defines the nucleus and contains nuclear pores that allow molecules to move in and out

what is the endoplasmic reticulum

produces many proteins and lipids, rough er protein synthesis, and smooth er fatty acid and phospholipid synthesis

Golgi apparatus

further modifies proteins and lipids, sorts them to their final destinations, and synthesizes carbs

lysosomes

degrade proteins, nucleic acids, lipids, and complex carbs

vesicles

transport materials between organelles

plasma membrane

defines the cell boundary and participates in movement of materials into and out of the cell

what is exocytosis

a vesicle buds form the end-membrane system, the vesicle fuses with the plasma membrane, its contents are delivered outside the cell

endocytosis

material from outside the cell is brought into the cell in a vesicle and the vesicle can then fuse with other organelles

what is the mitochondria

it harnesses energy from chemical compounds, converts energy to ATP, and has an outer membrane and highly convoluted inner membrane

Chloroplasts

capture energy from the sun, it synthesizes simple sugar through photosynthesis and has a double membrane and internal thylakoid compartments containing pigments such as chlorophyll

cytosol free ribosomes

proteins re produced in the cytosol, they re sorted to their final destination after translation, sorting is directed by specialized amino sequences called signal sequences, proteins without a signal remain in the cytosol, and signals can target proteins to the mitochondria, chloroplasts, or nucleus

rough er

proteins made by ribosomes on the RER can enter the er lumen, become embedded int he er membrane, or eventually be secreted outside the cell.

what is the process of transmembrane protein targeting

a single anchor sequence is encountered, the SAC is hydrophobic, the RER channel releases the protein into the membrane, the signal anchor sequence diffuses laterally in the lipid bilayer, the ribosome dissociates from the channel, translation continues, the completed protein has its carboxyl end on the cytosolic side and amino end in the lumen, these proteins can remain in the ER membrane or eventually reach the plasma

what are the four essential elements of cell communication

signaling cell, signaling molecule, receptor molecule, receptor cell

what are the four steps in cell signaling

receptor activation, signal transduction cell response and termination

what is receptor activation

the signal binds to its receptor

signal transduction

the signal is transmitted to theinteriror of the cell through a signaling pathway

cell response

by activating and enzyme or turning on a gene