CELL 305 1.3 - The Cell & Protein Synthesis

what is the function of the cell membrane?

- encloses the nucleus

- regulates what enters and leaves the cell

- separates the cell contents from its surroundings

what is the function of the cell nucleus?

- Contains genetic material (DNA)

- control center of the cell

what is the function of the cytosol?

where many chemical reactions occur

what is the function of ribosomes?

protein synthesis

what is the function of the rough ER (endoplasmic reticulum)?

synthesizes proteins for secretion and membrane construction

what is the function of the smooth ER (endoplasmic reticulum)?

- lipid and steroid synthesis

- protein modification

- packages proteins in vesicles after translation

what is the function of the golgi apparatus?

- sorts and modifies proteins

- packages secretory vesicles for release by exocytosis

- sorts and directs the finished products to their final destinations

what is the function of the mitochondria?

cellular respiration and production of ATP

what is the function of lysosomes?

- digest extracellular material brought into the cell by phagocytosis

- remove worn-out organelles

what is the function of peroxisomes?

house oxidative enzymes that detoxify wastes

what is the function of the cytoskeleton?

- serves as the cells "bone and muscle"

- regulates movement

- gives cell its shape

where is DNA found?

nucleus

what are the functions of DNA in protein synthesis?

- serves as genetic blueprint during cell replication

- in the nucleus, DNA is transcribed into mRNA

what are the three parts of the nucleotides that make up DNA?

- sugar

- phosphate

- base

what are the 4 different bases in DNA?

- purines: adenine (A), guanine (G)

- pyrimidines: cytosine (C), thymine (T)

mRNA role in protein synthesis

travels to ribosome, which reads its instructions to build a protein from amino acids

role of rRNA in protein synthesis

forms part of ribosome structure

role of tRNA in protein synthesis

- delivers amino acids to their site in the protein under construction at the ribosome

- complementary base pairing - matches codons on the mRNA with anticodons in rRNA

in base pairing, which bases pair with each other?

- T-A (thymine pairs with adenine)

- G-C (guanine pairs with cytosine)

which three bases code for methionine?

AUG

which three bases pair for glycine?

CCG

what determines the type of protein that will be made?

- sequence of bases

- amino acid sequence

what is a gene?

a stretch of DNA that codes for the synthesis of a given polypeptide or protein

what is a chromosome?

- a long, tightly coiled strand of DNA wrapped around proteins

- like a library bookshelf full of books (genes), each book has a recipe for building a protein

- the gene needed for making a specific protein is located in a chromosome in the nucleus

- a section of DNA on the chromosome is unwound and copied into mRNA

where does transcription happen?

nucleus

explain the process of transcription

- DNA is transcribed into mRNA in the nucleus by RNA polymerase

- RNA polymerase reads the DNA strand and adds complementary RNA nucleotides to build an RNA strand

what is the major enzyme complex that performs transcription?

RNA polymerase

explain the process of translation initiation

- small ribosomal unit binds to mRNA

- rRNA with methionine is loaded into small ribosomal unit

- large ribosomal unit binds

- A-site is where tRNA enters the ribosome and is tested for a codon/anticodon match with the mRNA

- P-site is where peptide bond is formed between amino acids

- E-site is where the used tRNA is ejected from the ribosome and recycled

explain the process of translation elongation

- peptide bond forms between amino acids

- tRNA with next amino acid to be added to polypeptide

- tRNA is released from P side

- ribosome moves over one codon

- new tRNA binds to A site

- new peptide bond forms between amino acids

- process repeats

summarize the process of translation

- mRNA attaches to small ribosomal unit

- methionine-tRNA binds to 3 bases on mRNA (AUG)

- large ribosomal subunit binds to this complex

- another tRNA with a second amino-acid binds to the codon at the A site

- a peptide bond is formed between the two amino acids

- the ribosome moves one codon down the mRNA so that the first tRNA is now the E-site, the second tRNA is the P-site, and the A-site is empty

- another tRNA with a third amino-acid binds to the codon at the A-site

- a peptide bond is formed between the 2nd and 3rd amino acid

- this process is continued until a stop codon is reached, at which time the peptide chain is released

which amino acid is always the first to be added?

methionine

what is always the first start codon?

AUG

where does translation occur?

ribosomes

what are codons?

groups of three letters of the mRNA that are read by the small subunit of the ribosome

what is an anticodon?

the corresponding 3-base sequence on the tRNA that is paired with the codon on the mRNA

what is the role of the leader sequence in a newly translated protein?

determines where the newly translated protein will go

what is the leader sequence?

the first part that is translated