Topic 8: The Control Of Gene Expression Flashcards
1
Q
3.8.1 Changes of base sequence in DNA alters structure of proteins
What is a mutation?
A
- A change in the base sequence of DNA
- Often arise spontaneously during DNA replication
2
Q
What are some forms of mutation?
A
- Addition
- Deletion
- Substitution
- Inversion
- Duplication
- Translocation of bases
3
Q
What are addition and deletion mutations?
A
- Where one or more nucleotides (bases) are either inserted or deleted from the DNA sequence
- This type of mutation alters the sequence of nucleotides after the insertion/deletion point known as a frameshift
4
Q
What is a substitution mutation?
A
- Where one nucleotide (base) in the DNA sequence is replaced by another
5
Q
What is a duplication mutation?
A
- Where one or more nucleotides (bases) duplicate and repeat and therefore produces a frameshift
6
Q
What is an inversion mutation?
A
- Where a group of nucleotides (bases) become seperated from the DNA sequence then rejoin in the reverse order i.e. they have flipped
- This therefore affects the amino acid that is produced
7
Q
What is a translocation mutation?
A
- Where a group of nucleotides (bases) become seperated from the DNA sequence and are then inserted into the DNA of a different chromosome
- This can often lead to significant effects on the phenotype
8
Q
Which mutations are most likely to have a significant impact and why?
A
- addtion, deletion, duplication, translocation
- Because they produce a frameshift which means the entire amino acid sequence will be produced different
9
Q
Which mutations are less likely to have a significant impact and why?
A
- Substitution, Inversion
- Because they only alter one or very few triplets the amino acid sequence might not be affected due to the degenerate nature of the genetic code
10
Q
Is a mutation resulting in a change to the amino acid sequence always harmful and why?
A
- No, it may be neutral if the resulting change in protein has no effect on the organism
- Also may be beneficial, which is the basis for evolution and natural selection
11
Q
How is the mutation rate increased?
A
- by mutagenic agents
12
Q
What is a mutagenic agent? Give examples of this
A
- factors that increase the rate of gene mutation
- chemical mutagens such as alcohol and benzene
- Ionising radiation such as UV and X-Ray
13
Q
3.8.2.1 Most of a cells DNA is not translated
What is a stem cell?
3.8.2 Gene expression is controlled by a number of features
A
- Undifferentiated cells that can divide indefinitely and turn into other specific cell types
14
Q
Name and define the four types of stem cells?
A
- Totipotent- can develop into any cell type which can include the placenta and embryo
- Pluripotent- can develop into any cell type but EXCLUDING the placenta and embryo
- Multipotent- can only develop into a few different types of cell
- Unipotent- these cells can only differentiaate into one type of cell
15
Q
What happens to totipotent cells during embryonic development?
A
- Certain parts of the DNA are selectively translated so that only some genes are “switched on” in order to differentiate the cell into a specific type and to form the tissues that make up the foetus
16
Q
Give a unique feature of pluripotent cells and then the use of this feature
A
- They can divide in unlimited numbers and therefore can be used to repair and replace damaged tissues
17
Q
What is a unipotent cell? Give an example
A
- A cell that can only develop into one type of cell
- This happens at the end of specialisation when the cell can only propogate its own type
- An example is cardiomyocytes (heart cells)
18
Q
Which types of stem cells are found in embryos?
A
- Totipotent and Pluripotent
- Multipotent and unipotent cells only found in mature mammals
19
Q
Give some uses of stem cells
A
- Medical therapies-e.g. bone marrow transplants, treating blood disorders
- Drug testing-on artificially grown tissues
- Research-e.g. on **formation of organs and embryos
20
Q
How are induced ploripotent stem cells produced?
A
- From mature, fully specialised (somatic) cells
- The cell regains capacity to differentiate through the use of proteins, in particular transcription factors
21
Q
3.8.2.2 Regulation of transcription and translation
What is a transcription factor?
3.8.2 Gene expression is controlled by a number of features
A
- A protein that controls the transcription of genes so that only certain parts of the DNA are expressed
- they bind to a specific site on DNA to begin the process of transcription
- e.g. in order to allow the cell to specialise
22
Q
How do transcription factors work?
A
- move from the cytoplasm into nucleus
- bind to promoter region upstream of target gene
- makes it easier or more difficult for RNA polymerase to bind to gene, this increases or decreases the rate of transcription
23
Q
Give an example of a hormone that affects transcription and explains how it works
A
- Steroid hormone oestrogen diffuses through cell membrane
- Forms hormone-receptor complex with ER a receptor in the cytolasm
- Complex enters the nucleus and acts as a transcription factor to facilitate the binding of RNA polymerase
24
Q
What is the role of oestrogen in controlling transcription?
A
- The lipid soluble nature of oestrogen means that it can freely diffuse across the cell
membrane where it binds to a receptor molecule on a transcription factor - The binding alters the shape of the DNA binding site on the transcription factor and makes it able to bind to the DNA
- The transcription factor therefore enters the nucleus via the nuclear pore where it binds to DNA
This stimulates the transcription of the gene that makes up the DNA
25
What is small interfering RNA?
* also called **silencing RNA** is used for short term **switching off of genes**
* **siRNA binds** to a **complementary sequence of mRNA**
* **mRNA** is usually **single stranded** and the **cell therefore detects** the **double stranded form on mRNA** and **views it as abnormal**
* Therefore the **mRNA is broken down by enzymes preventing translation**
26
What is meant by epigenetics?
* A **heritable change** in the **gene function** **WITHOUT change** to the **base sequence of DNA**
* shows that **environmental factors** can **make changes** to the **function of genes** which can be **inherited**
27
How does increased methylation of DNA affect gene transcription?
* Involves **addition of CH3 group** to **cytosine bases** which are **next to guanine**
* **prevents transcription factors from binding**
* therefore **gene transcription** is **supressed**
28
How does decreased acetylation of histones affect gene transcription?
* **positvely charged histones bind** to **negatively charged DNA**
* **decreasing acetylation increases positive charge of histones**
* **binding** becomes **too tight** and **prevents transcription factors** from **accessing the DNA**
* so **transcription is supressed**
29
How might epigenetic changes affect humans?
* They can **cause disease** either **by activating a genes function** (such as in cancer) or **by supressing it**
30
Give an application of epigenetics
* Treatment of various diseases
* Development of ways to reverse epigenetic changes
31
Describe the process of RNA interference including the organisms in which it occurs
* **RNA molecules** act to **inhibit gene expression** usually **by destroying mRNA** so that **it cannot be translated**
* **occurs** in **eukaryotes** and **some prokaryotes**
32
# **3.8.2.3 Gene expression and cancer**
Give some characteristics of benign tumours
| **3.8.2 Gene expression is controlled by a number of features**
* **slow growth**
* defined by a **clear boundary** due to **cell adhesion molecules**
* **Cells retain function** and **normal shape**
* **dont spread easily**
* **easy** to **treat**
33
Give some characteristics of malignant tumours
* **rapid** and **uncontrollable growth**
* **III defined boundary**
* **Cells DO NOT retain function** and they **often die**
* **spreads quickly** and **easily**
* **difficult** to **treat**
34
Describe the role of tumour-suppressive genes
* **code for proteins that control cell division** in particular **stopping the cell cycle when damaged is detected**
* they are also involved in **programming apoptosis** i.e. **self destruction of the cell**
35
Explain how tumour-supressing genes can be involved in developing cancer
A **mutation in** the **gene** could **code for a nonfunctional protein**
* **Increased methylation** or **decreased acetylation** could **prevent transcription**
* **cells** will **divide uncontrollably resulting** in a **tumour**
36
Describe the role of proto-oncogenes
* **control cell division** in particular they **code for proteins that stimulate cell division**
37
Explain how proto-oncogenes can be involved in developing cancer
* **mutation in** the **gene** could **turn it into** a **permanently activated oncogene**
* **Decreased methylation** or **increased acetylation** can **cause excess transcription**
* results in **uncontrolled cell division** and the **formation** of a **tumour**
38
Explain how abnormal methylation of genes cause cancer
* **Hyper-methylation** of **tumour-suppressor genes** or **oncogenes** can **impair their funtion** and **cause the cell to divide uncontrollably**
39
Explain how oestrogen can be involved in developing breast cancer
* **oestrogen** is an **activator of RNA polymerase**
* therefore **in areas** with a **high concentration of oestrogen** such as **adipose tissue in the breasts**, **cell division** can **become uncontrolled**
40
# **3.8.3 Using genome projects**
What is the genome?
* the **complete set** of **genetic information** contained **in the cells of an organism**
41
What is genome sequencing?
* **Identifying** the **DNA base sequence** of an **individual**
* This **allows us** to **determine** the **amino acid sequence of the polypeptides coded for by that DNA**
42
What is the proteome?
* the **complete set** of **proteins** that **can be produced by a cell**
43
Can we directly translate the genome into the proteome?
* in **simple organism** **YES**
* in **complex organisms due to the presence of non-coding DNA** and **regulatory genes**, it is **much harder** to **obtain the proteome**
44
Give an application of sequencing the proteome in single organisms
* **identifying potential antigens** for **use in vaccine production**
45
Give some applications of genome sequencing
* **comparing genomes** between **species** to **determine evolutionary relationships**
* **genetic matching**
* **personalised medicine
* **synthetic biology**
46
How have sequencing methods changed over time?
* **was** a **manual process**
* **now** it has **become automated**
* a **reaction mixture** is **created** and **after** the **process is complete** a **machine reads** the **base sequence**
47
# ****3.8.4.1 Recombinant DNA technology****
What is meant by recombinant DNA technology?
| **3.8.4 Gene tech allows the study/alteration of gene function**
* the **transfer** of **DNA fragments** from **one organism or species to another**
48
Why does recombinant DNA technology work?
* because the **genetic code** is **universal** and therefore **transcription** and **translation occur** by the **same mechanism** and **result** in **the same amino acid sequence across organisms**
49
Summarise the process of using reverse transcriptase to produce DNA fragments
* **mRNA complementary to** the **target gene** is **used as** a **template**
* it is **mixed with free nucleotides** which **match up to their base pairs** and **reverse transcriptase** which **forms** the **sugar phosphate backbone** to **create cDNA (complementary DNA)
50
Summarise the process of using enzymes to produce DNA fragments
* **restriction endonucleases cut DNA at specific sequences**
* **different REs** will **ALWAYS cut at the SAME sequence**
* therefore **using particular REs allow you to cut out a certain gene of interest**
51
In which two ways can we amplify DNA fragments
* ****in vitro****/ **polymerase chain reaction**
* ****In vitro****/ **using host cells**
52
Describe the reaction mixture in the first stage of PCR
* **contains** the **DNA fragment** to be **amplified**,
* **primers** that are **complementary to** the **start of the fragment**
* **free nucleotides** to **match up to exposed bases**
* **DNA polymerase** to **create new DNA**
53
Summarise the process of amplifying DNA fragments using PCR
1. **Heated** to **break apart** the **DNA strands**
2. **Cooled** which **allows primers to bind**
3. **Heated again** to **activate DNA polymerase** and **allow free nucleotides to join**
4. **New DNA acts as** a **template** for **next cycle**
54
Summarise the process of inserting a DNA fragment into a vector
* A **plasmid used as** the **vector** and is **cut using** the **same restriction enzymes as DNA** so that the **ends are complementary**
* **DNA ligase joins fragment** and **plasmid together**
55
Summarise the process of inserting a vector into a host cell
* known as **cell transformation**
* the **host cells** are **mixed with vectors in** an **ice-cold solution**, then **heat shocked to encourage cells to take up the vectors**
* **Cells can then** be **grown** and the **DNA fragment** will be **cloned**
56
Summarise the process of identifying transformed cells
* **marker genes** e.g coding for fluoroescence can also be insterted into vectors along with DNA
* when **cells begin to grow**, **UV light** can be **used to identify** which **cells have taken up the vector and which havent**
57
# **3.8.4.2 Differences in DNA between individuals of the same species..**
How can DNA probes be used to locate specific alleles?
| **3.8.4 Gene tech allows the study/alteration of gene function**
* **probe designed** so that its **sequence is complementary to the allele** you want to find
* they are **labelled, amplified using PCR** then **added to a sample of single stranded DNA**
* The **probe** will **bind if** the **allele is present**
58
Give some applications of DNA probes
* To **screen someones DNA** for a **particular heritable health condition**
* To **identify a gene** for **use in genetic engineering**
* To **predict how someone will respond to a drug**
59
What is the purpose of hybridisation?
* to **measure degree** of **difference between two strands of DNA**
* can be **used to compare someones DNA** to a **certain gene** to **see if the have it**
60
Summarise the process of DNA hybridation
* **one DNA strand** is **labelled** and **mixed with an unlabelled comparison strand**
* the **more similar the strands** the **more strongly they will bind** and **more energy** will be **required** to **break the strands apart**
61
What are the benefits of genetic profiling?
* can **identify heritable diseseases very early** therefore **begin** to **treat them before symptoms develop, reducing impact on individual
* **treatment can** also be **personalised** to **make it more effective**
62
What is genetic fingerprinting?
* technique used to **compare two DNA samples** and **determine whether they came from the same individual**
63
How does genetic fingerprinting work?
* every **organisms genomes contains non-coding regions called variable number tandem repeats (VNTRs)**
* the **probability** of **two individuals having** the **same VNTRs** is **very low** so **we can compare these areas to see if two DNA samples came from the same person**
64
Summarise the process of genetic fingerprinting analysis
- **DNA sample** is **obtained**
- **VNTRS cut out using restriction enzymes**
- They are then **labelled** and **cloned using PCR**
- **fragments** are **separated using gel electrophoresis**
- **banding patterns of each sample** can then be **compared**
65
How does gel electrophoresis work?
- **DNA fragments** are **placed** at **one end** of a **slab of gel**
- An **electric current** is **applied causing** the **DNA fragments to move towards the other end of the gel**
- **Shorter fragments travel further**
- The **pattern of bands created** is **unique to every individual**
66
Give applications of genetic fingerprinting
- **Forensics**- e.g. to **identify victims or suspects**
- **Medical diagnosis**- e.g. to **identify type of haemoglobin produced** by an individual to **diagnose sickle cell anaemia**
- **Animal** and **plant breeding**- e.g. **breed out harmful alleles** and **ensure pedigree**
