3.4- Chapter 8- DNA, genes and protein synthesis Flashcards
1
Q
What is biodiversity reflected by?
A
Biodiversity is reflected in the vast numbers of species of organisms, in the variation of individual characteristics within a certain species and in the variation of cell types within the single multicellular organism.
2
Q
What are differences between species/ individuals caused by?
A
- Differences between species reflect genetic differences
- Differences between individuals within species could be the result of genetic/ environmental factors.
3
Q
What do changes in base sequences do?
A
- Changes in base sequenxes produce a new allele of that gene- mutation.
- This results in different sequence of amino acids, polypetides and protiens, with different primary and tertiary structure.
- Sometimes this means the protein won’t function properly or at all e.g., enzymes.
4
Q
How is DNA stored in prokaryotes?
A
- Still carry DNA as chromosomes- one single circular one.
- DNA is in the cytoplasm.
- DNA is shorter and circular.
- DNA isn’t associated with histones.
- Condenses to fit cells by supercoiling.
- No introns.
- Can have plasmids.
5
Q
How is DNA stored in Eukaryotes?
A
- In the nucleus.
- Linear.
- Exists as chromosomes.
- One longer molecule of DNA and proteins.
- Has introns.
- Associated with proteins called histones to fit in the nucleus- help support DNA.
- DNA- coiled tightly into compact chromosomes.
- No plasmids.
6
Q
How is DNA stored in mitochondria/ chloroplasts?
A
- Similar to structure of DNA in prokaryotes.
- Shorter- fewer genes.
- Circular not linear
- Not associated with histone proteins, unlike nuclear DNA.
- No introns, unlike nuclear DNA.
7
Q
What do all forms of DNA have in common?
A
- Phosphodiester bonds between phosphate and deoxyribose of nucleotides
- Phosphodiester bonds formed in a condensation reaction catalysed by DNA polymerase.
- Nucleotide structure is identical.
8
Q
What must you say when comparing different DNA?
A
- Use comparative language (and state both factors comparing e.g. prokaryotes and eukaryotes).
- Remember compare and contrast= similarities as well as differences.
9
Q
What is a gene?
A
Gene- section of DNA which occupies a fixed position on a particular DNA molecule called a locus.
10
Q
What does the base sequence of each gene carry.
A
Base sequence of each gene- carries coded genetic information- determines the sequence of amino acids during protein synthesis.
11
Q
What do genes code for and what is the structure of htis code.
A
- Genes either code for a polypeptide (sequence of amino acids- primary structure) or functional RNA.
- The code is in the specific base sequence that determines the order of amino acids- primary structure- each amino acid is coded for by 3 bases in a gene called a triplet or codon.
- The code may also determine functional RNA- RNA that isn’t mRNA- tRNA or rRNA.
12
Q
What do polypeptides form?
A
Proteins
13
Q
What is the genome?
A
Complete set of genes in a cell.
14
Q
What is the proteome?
A
Full range of proteins a cell is able to produce.
15
Q
What about the genetic code provides indirect evidence for evolution?
A
Same in all organisms.
16
Q
What is hte reasoning behind the triplet code?
A
- Genetic code- same in all organisms- indirect evidence for evolution.
- Reasoning- 20 amino acids- each has it’s own code, only 4 bases.
- 4^1 and 4^2 wouldn’t provide enough codes for all the amino acids so has to be 43.
- There are 64 possible triplets and 20 amino acids- some coded more than one triplet.
17
Q
What are the key features of the genetic code?
A
- Degenerate- most amino acids are coded for by more than one codon and some triplets don’t code for amino acids.
- Unidirectional- always read in the same direction.
- Start codon- amino acid methionine- for polypeptides, removed if not part of the product later.
- Stop codon- 3 triplets- mark end of polypeptide chain- don’t code for amino acids.
- Non-overlapping- base sequences read only once, separate from triplet before and after, don’t share bases.
- Universal- triplet codes the same in all organisms- codes for the same amino acids- indirect evidence for evolution.
18
Q
What can parts of the genetic code be and in what type of cell must it be for this to occur.
A
- Parts of the genetic code can be non-coding in eukaryotes (but not eukaryotes)- lots of DNA in the nucleus doesn’t code for polypeptides or functional RNA (tRNA/ mRNA)
- Non coding DNA- doesn’t code for amino acid/ tRNA/ rRNA.
- Non-coding regions may be introns.
- May also be non-coding multiple repeats of base sequences between genes that don’t code for a sequence of amino acids e.g. CCTTCCTTCCTT.
19
Q
What are exons?
A
Base sequences within genes that code for a sequence of amino acids.
20
Q
What are introns?
A
Non-coding sequences of DNA that separate exons- may be several in a gene, removed during splicing in protein synthesis.
21
Q
When are chromosomes visible and what are htey otherwise?
A
Structure only visible within a cell if dividing otherwise widely dispersed.
22
Q
What do chromosomes look like during cell division?
A
- 2 chromatids joined at the centromere.
- Chromatids- 2 identical DNA molecules.
23
Q
How is DNA stored/ packaged?
A
- DNA- held by histones and highly coiled to store it all. Helix is wound around histones for fixed position then coiled then looped then coiled then packaged into chromosomes.
- DNA is condensed into a single chromosome made of just one very long molecule of DNA with many genes with a specific locus.
24
Q
What is the number of chromosomes like for same/ different species?
A
- The number of chromosomes is always the same for the same species and varies form one to another although it is often even.
- E.g. Humans have 46 chromosomes or 23 pairs of chromosomes.
25
What organisms have homologous pairs of chromosomes?
Eukaryotic sexually produced organisms
26
Describe homologous pairs.
* **2 chromosomes that carry the same genes.**
* Homologous pairs of chromosomes- 1 maternal and 1 paternal. Total number is diploid e.g. 46.
* In a homologous pair each chromosome has the same number (e.g. chromosome 1), size and genes. However they may contain different alleles.
* Alleles coding for the same characteristic would be found at the same locus (fixed position) on each chromosome.
27
What does meiosis ensure in terms of homologous chromosomes?
Ensures one chromosome form each homologous pair so each cell has one gene for each characteristic- haploid. Combine into diploid state- homologous chromosomes restored.
28
What are alleles and what happens is alleles are different?
* Alleles- same gene but in different form- often two but can be one.
* One allele is inherited from each parent.
* If alleles are different- slightly different base sequence- slightly different version of the same polypeptide.
* Alleles may be caused by mutations.
29
What does RNA stand for?
Ribonucleic acid.
30
What is RNAs role?
Transfers genetic information form DNA out of the nucleus to the ribosomes in the cytoplasm.
31
What is RNA's general structure?
A single polynucleotide chain made of nucleotides with Guanine, Cytosine, Adenine and Uracil bases (uracil replaces thymine), a phosphate group and a ribose pentose sugar.
32
What does mRNA stand for?
Messenger RNA
33
What is mRNA's structure?
* **Longer, linear (no hydrogen bonds), more nucleotides than tRNA.**
* Coiled into a helix
* Acts as a template for protein synthesis.
* Contains **codons** (3 bases complementary to a triplet) that determine the amino acid sequence.
* No hydrogen bonds (don’t mention with linear as the same thing).
34
What is mRNA's function?
* Messenger RNA.
* Made during transcription.
* Small enough to leave the nucleus through nuclear pores.
* Carries the genetic code from DNA to ribosomes for transcription.
35
What does tRNA stand for?
Transfer RNA.
36
What is tRNA's function?
* Used during translation.
* Must be as many tRNA as coding triplets each specific to one amino acids.
37
Describe the structure of tRNA.
* Smaller than mRNA, single stranded, folded into a **clover leaf shape.**
* One end contains a specific amino acid binding site.
* Opposite end- contains 3 bases- the **anticodon**.
* Held in shape by **hydrogen bonds.**
38
What is the third type of RNA and what does it do?
**rRNA- combines with proteins to form ribosomes. **
39
What are proteins made from?
Made of one or more polypeptides- made from 20 amino acids.
40
What are the stages of protein synthesis?
1. Translation- DNA code is copied into mRNA.
2. Splicing- mRNA is edited.
3. Translation- ribosome synthesises protein.
41
Give an overview of transcription.
mRNA copy made from DNA- takes place in the nucleus or in the cytoplasm in prokaryotes.
42
Describe transcription.
1. RNA polymerase attaches to DNA at the beginning of a gene. **Hydrogen bonds** in the gene are **broken** by DNA helicase attached to the RNA polymerase (in eukaryotes). The DNA uncoils and separates into two strands exposing nucleotide bases. **One strand is then used as a template strand.**
2. **RNA polymerase lines up free-floating RNA nucleotides **alongside complementary exposed bases on the template strands.
3. **Complementary base pairs** attract by the complementary base pairing rule- **GCAT/ GCAU.**
4. Once the bases have paired the **adjacent RNA nucleotides are joined by RNA polymerase in a condensation reaction forming phosphodiester bonds.**
5. As RNA polymerase moves along the DNA- hydrogen bonds between DNA reform once RNA polymerase passes- recoils into double helix.
6. RNA polymerase builds pre-mRNA. Once it reaches a stop triplet it stops making pre-mRNA and detaches from DNA.
7. **Pre-mRNA is then spliced into mRNA.**
8. mRNA moves out of the nucleus and attaches to a ribosome.
43
What must you mention if hte question asks about mRNA?
**Pre-mRNA being spliced**
44
Where does splicing happen and why does it occur?
* Splicing happens in eukaryotes- pre-mRNA forms.
* Eukaryotes have introns which are copied along with exons into pre-mRNA in transcription. Prokaryotes don’t need splicing as they don’t have introns.
* Introns don’t code for proteins and prevent protein synthesis.
45
Describe splicing.
* **Introns base sequences are removed** during splicing and their exons are joined together forming mRNA in the nucleus **made of just exons.**
* The mRNA leaves the nucleus by a nuclear pore.
46
Give an overview of translation.
* Translation occurs in ribosomes. Codons of mRNA are translated into a polypeptide chain of amino acids by tRNA with specific anticodons attached to different amino acids.
* ATP provides the energy for translation to occur.
* Degenerate genetic code means some amino acids have more than one tRNA.
47
Describe the process of translation.
1. **Ribosome attaches to** start codon (AUG) on **mRNA**.
2. **tRNA** with **complementary anticodon binds with the codon on mRNA** by complementary base paring rule. The tRNA carries a **specific amino acid.** Codons- 3 bases determined by genes.
3. The process is repeated on the next codon- another tRNA molecule with complementary anticodon pairs by complementary base pairing rule with the next codon on the mRNA. The tRNA carries an amino acid.
4. The 2 amino acids are joined together by a **peptide bond in a condensation reaction using an enzyme and ATP hydrolysis.**
5. The **ribosome moves along the mRNA and brings together two tRNA molecules** at a time. As this happens the first **tRNA is released** leaving its amino acid behind and is free to collect another.
6. The process repeats until the ribosome reaches a stop codon and the ribosome, mRNA and tRNA molecules sperate. The **polypeptide chain** is completed. Multiple ribosomes can be attached to mRNA at a time making multiple polypeptides.
48
Describe how proteins are processed after translation.
The polypeptide is coiled and folded into the secondary and tertiary structure and linked with other chains and non-protein prosthetic groups to form the quaternary structure.
49
Describe how you would give a DNA sequence for amino acids from a table.
Work out complementary copy of mRNA- swap T for U.
50
Describe how you would give tRNA anticodons.
Give complimentary copy of mRNA codon.
51
Describe how you would write an amino acid sequence.
Use mRNA and break into codons of 3.
52
How do you interpret data from experiments on nucleic acids e.g. effects of drugs.
* Interpreting data from experiments on nucleic acids and their role in protein synthesis- analyse difference between factors e.g. for the effect of drugs.
* One factor may affect transcription (e.g. due to mRNA being digested by an enzyme)= less/ no mRNA= less/ no translation.
* One factor may limit translation- mRNA present but no protein- may interfere with tRNA- e.g. may be a similar shape, bind to ribosome and block tRNA.
