BIOL 15b Lecture Notes - Lecture 4: Chromosome, Tata Box, Rna Splicing

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4 Feb 2017
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Lecture 4: 1/25
DNA replication:
Function - encode genetic material
DNA polymer chains wind around each other in a double helix
Each purine base forms hydrogen bonds with pyrimidine base
DNA is read from 5’ to 3’
5’ end - phosphate group
3’ end - hydroxyl group
DNA strands are antiparallel
- The outside contours of the twisted strands form an uneven pair of grooves, called the
major groove and the minor groove
- Due to hydrogen bonds, base pairing is always the same
Structure:
- Base stacking caused by non-polar bases excluding water, also stabilizes DNA
- Either strand can act as a template for DNA replication
DNA must be uncoiled before it can be used
- DNA is coiled around histones to condense so it takes up less space
- Always adds nucleotides to the 3’ end (5’ → 3’)
- 2 parental strands separate at a replication fork and each allows for the formation of a
daughter strand
DNA replication:
- Helicase unwinds the DNA double strand
- Topoisomerase 2 helps to unwind DNA also
- Single strand binding proteins stabilize the single strands when unbonded
- Leading and lagging strands (okazaki fragments)
1. Initiated with RNA primer
2. DNA polymerase adds to primer
3. DNA ligase fuses daughter strand fragments
- Errors are made!
DNA replication happens in both directions at once:
- DNA polymerase proofreads the strand as it is created and corrects errors as it goes
- It is not perfect at proofreading…
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Lecture 5: 1/26
Cancer cells:
- Cells grow and divide uncontrollably
- Cells don’t die
- Cells promote blood vessel development
- Malignant cells invade other tissues
DNA is long and cell division needs to happen quickly
- Multiple replication forks
- Replication bubbles
Bacterial mitochondrial, chloroplast DNA replication - happens in a circle DNA molecule
Chromosomes:
- With each successive replication linear DNA strands become shorter
- Telomeres added to the end of each chromosome so we don’t lose “gene”
- Telomeres shortened with replication but then lengthened again by telomerase
Telomeres
- 5’ - TTAGGG - 3’ repeated over and over at the ends of chromosomes
Central dogma of biology
- DNA (replication) → transcription→ RNA → translation→ Proteins
- DNA encodes genetic information
RNA
- DNA molecules are too big to shuttle around the cell constantly
- Only need one part of instruction at a time
Transcription:
- Copying DNA to RNA
- Facilitated by RNA polymerase (a protein enzyme)
- All genes start with a promoter sequence (TATA box)
- All genes end with a terminator sequence
Housekeeping genes:
- Genes that are transcribed at all times
- Required by all calls at all times
- Genes that create proteins by transcription factors
Non-housekeeping genes:
- most genes are transcribed only in some cells or only at certain times
- Transcription regulated by transcription factors
Enhancer sequences are found near the promoter
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