TRANSCRIPTION AHL Topic 7 3 IB Biology Miss

TRANSCRIPTION AHL Topic 7. 3 IB Biology Miss Werba

AHL TOPIC 7 – NUCLEIC ACIDS AND PROTEINS 7. 1 DNA STRUCTURE 7. 6 ENZYMES 7. 2 DNA REPLICATION 7. 5 PROTEINS 7. 3 TRANSCRIPTION 7. 4 TRANSLATION J WERBA – IB BIOLOGY 2

THINGS TO COVER �Direction of transcription �Sense and antisense strands of DNA �Prokaryotic transcription: ◦ promoter region, RNA polymerase, NTPs & the terminator �Eukaryotic transcription J WERBA – IB BIOLOGY 3

7. 3. 1 DIRECTION OF TRANSCRIPTION Command term = STATE �Transcription is carried out in a 5’→ 3’ direction. � This means the 5’ end of the RNA strand � The 5’ end of the free RNA nucleotide is added to the 3’ end of the RNA molecule that is already synthesized. � Addition of nucleotides is catalysed by RNA polymerase. J WERBA – IB BIOLOGY 4

SENSE and ANTISENSE STRANDS 7. 3. 2 Command term = DISTINGUISH � Sense strand: ◦ the coding strand of DNA - ie. it contains the genes ◦ not transcribed! � Antisense strand: ◦ also known as the template strand ◦ complementary to the sense strand ◦ transcribed into m. RNA � Why? ◦ By transcribing the antisense strand, the base sequence of the m. RNA will be the same as the coding DNA (except U replace T) J WERBA – IB BIOLOGY 5

7. 3. 3 PROKARYOTIC TRANSCRIPTION Command term = EXPLAIN � Transcription in prokaryotes involves a number of elements: 1. A promoter region 2. Attachment of ribonucleoside triphosphates 3. RNA polymerase 4. A terminator region J WERBA – IB BIOLOGY Ref: IB Biology, Oxford Study 6

PROKARYOTIC DNA REPLICATION 7. 2. 2 Command term = EXPLAIN 1) The promoter region � The promoter region is found on the sense strand � Specific sequence of DNA bases that acts as a binding point for RNA polymerase � RNA polymerase unwinds small sections of DNA J WERBA – IB BIOLOGY 7

PROKARYOTIC DNA REPLICATION 7. 2. 2 Command term = EXPLAIN 2) Ribonucleoside triphosphates & RNA polymerase � RNA polymerase adds ribonucleoside triphosphates to the DNA antisense strand using complementary base pairing � NTPs are added to the 3’ end of the RNA strand. � This forms messenger RNA (m. RNA) J WERBA – IB BIOLOGY 8

PROKARYOTIC DNA REPLICATION 7. 2. 2 Command term = EXPLAIN 3) The terminator region � The terminator region is also found on the sense strand � Specific sequence of DNA bases that acts as an end point for transcription � RNA polymerase breaks free and the m. RNA strand is released J WERBA – IB BIOLOGY 9

EUKARYOTIC TRANSCRIPTION 7. 3. 4 Command term = STATE �Eukaryotic RNA needs the removal of introns to form mature m. RNA. � Eukaryotic pre-m. RNA contains exons and introns ◦ Remember: exons stay in, introns move out � Introns are transcribed but not translated � Introns need to be removed before translation using splicing enzymes � This will form mature m. RNA, ready for translation. J WERBA – IB BIOLOGY 11

Sample questions Q 1. Where does the RNA polymerase bind during the process of transcription? The polysome B. The operator C. The promoter D. The initiator A. J WERBA – IB BIOLOGY 12

Sample questions Q 2. The sequence of nucleotides in a section of RNA is: GCCAUACGAUCG What is the base sequence of the DNA sense strand? CGGUAUGCUAGC B. GCCATACGATCG C. CGGTATGCTAGC D. GCCAUACGAUCG A. J WERBA – IB BIOLOGY 13

Sample questions Q 3. Explain the process of transcription leading to the formation of m. RNA. [8] J WERBA – IB BIOLOGY 14

Sample questions � A 1. C � A 2. B J WERBA – IB BIOLOGY 15

Sample questions A 3. � RNA polymerase; (polymerase number is not required) � binds to a promoter on the DNA; � unwinding the DNA strands; � binding nucleoside triphosphates; � to the antisense strand of DNA; � as it moves along in a 5′→ 3′ direction; � using complementary pairing/A-U and C-G; � losing two phosphates to gain the required energy; � until a terminator signal is reached (in prokaryotes); � RNA detaches from the template and DNA rewinds; � � � RNA polymerase detaches from the DNA; many RNA polymerases can follow each other; introns have to be removed in eukaryotes to form mature m. RNA; 8 max J WERBA – IB BIOLOGY 16