3.5, 3.6 - Nucleus, Protein synthesis Flashcards
1
Q
Describe the structure of the nucleus
A
Outer layer: Bilayer nuclear envelope, nuclear pores
Middle layer: Chromatin
Inner layer: Nucleolus
2
Q
Describe the structure of the nuclear envelope
A
- Bilayer that surrounds the nucleus
- continuous with the RER
- Nuclear pores present, surrounded by polyribosomes
3
Q
What is the function of nuclear pores?
A
- Mediates the movement of substances out of the nucleus
4
Q
What is chromatin?
A
- Cell’s genetic material
- Condensed
- Contained into the nucleus
5
Q
What is the structure and function of the nucleolus?
A
- Clusters of protein, DNA and RNA
- Contained inside the nucleus
- Sites of ribosome production
6
Q
What are the three steps to transcription?
A
- Initiation
- Elongation
- Termination
7
Q
What occurs generally during DNA transcription?
A
- Genetic information on DNA is transcribed into a complementary mRNA strand
8
Q
Describe the initiation stage of DNA transcription
A
- RNA Polymerase binds to the DNA strand
- Enzyme moves along the strand until it reaches a promoter region
- Transcription factors are also bound to the promoter region: control transcription
- At the promoter region RNA polymerase unwinds DNA strand
9
Q
Describe the elongation stage of DNA transcription
A
- Template strand is read in the 3’ to 5’ direction
- Provides a template for mRNA
- mRNA is produced from the template strand
- Resultant mRNA is identical to the coding strand of DNA
10
Q
Describe the termination stage of DNA transcription
A
- RNA polymerase reaches a stop sequence
- Transcription stops
- mRNA strand is released
- RNA polymerase unbinds
- DNA strand reformed
11
Q
What occurs during translation
A
- Occurs at a ribosome
- mRNA is converted into a specific amino acid sequence
12
Q
Describe the 6 stages of translation
A
- mRNA binds to the small ribosomal subunit. tRNA initiator binds to AUG start codon
- Large subunit joins to create a functional ribosome. tRNA fits into a specific position in the ribosome
- tRNA with complementary anticodon to the next mRNA codon joins next to the initiator
- Peptide bond formed between the two amino acids
- Empty tRNA molecule is released. Ribosome moves along to the next codon
- Steps 3-5 repeat until a stop codon is reached. protein detaches and the ribosome splits
13
Q
Describe the structure of tRNA
A
- Short RNA strand with two ends
- 1 end contains an anticodon
- Other end is bound to an amino acid coded for the complementary codon to the anticodon
14
Q
Describe the structure and function of a polyribosome
A
- Multiple ribosomes joined together
- Make many copies of the same protein at the same time
